Water on Mars

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Water on Mars
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{{About||the music group|Water on Mars (band)}}{{Use mdy dates|date=July 2018}}File:AncientMars.jpg|thumb|200px|right|An artist's impression of what ancient Mars may have looked like, based on geological data ]]{{multiple image|direction=vertical|align=right|total_width=200|header=Mars – Utopia Planitia |header_align=center|image1=PIA21136 - Scalloped Terrain Led to Finding of Buried Ice on Mars.jpg|caption1=Martian terrain|width1=640|height1=398|image2=PIA21138 - Location of Large Subsurface Water-Ice Deposit in Utopia Planitia, Mars.png|caption2=Map of terrain|width2=596|height2=286|footer_align=left
Scalloped topography>Scalloped terrain led to the discovery of a large amount of underground ice – enough water to fill Lake Superior (November 22, 2016)STAFF >TITLE=SCALLOPED TERRAIN LED TO FINDING OF BURIED ICE ON MARS DATE=NOVEMBER 22, 2016 NASA >ACCESSDATE=NOVEMBER 23, 2016, HTTPS://WWW.THEREGISTER.CO.UK/2016/11/22/NASA_FINDS_ICE_UNDER_MARTIAN_SURFACE/ >TITLE=LAKE OF FROZEN WATER THE SIZE OF NEW MEXICO FOUND ON MARS – NASA DATE=NOVEMBER 22, 2016 PUBLISHER=NASAACCESSDATE=NOVEMBER 23, 2016, }}Almost all water on Mars today exists as ice, though it also exists in small quantities as vapor in the atmosphere.BOOK, Jakosky, B.M., Haberle, R.M., 1992, The Seasonal Behavior of Water on Mars, Mars, H.H., Kieffer, etal, University of Arizona Press, Tucson, AZ, 969–1016, What was thought to be low-volume liquid brines in shallow Martian soil, also called recurrent slope lineae,JOURNAL, Transient liquid water and water activity at Gale crater on Mars, Nature Geoscience, April 13, 2015, Martín-Torres, F. Javier, Zorzano, María-Paz, Valentín-Serrano, Patricia, Harri, Ari-Matti, Genzer, Maria, 10.1038/ngeo2412, 8, 5, 357–361, 2015NatGe...8..357M, JOURNAL, Ojha, L., Wilhelm, M. B., Murchie, S. L., McEwen, A. S., Wray, J. J., Hanley, J., Massé, M., Chojnacki, M., 2015, Spectral evidence for hydrated salts in recurring slope lineae on Mars, Nature Geoscience, 10.1038/ngeo2546, 8, 11, 829–832, 2015NatGe...8..829O, may be grains of flowing sand and dust slipping downhill to make dark streaks.Recurring Martian Streaks: Flowing Sand, Not Water?, 2017-11-20 The only place where water ice is visible at the surface is at the north polar ice cap.BOOK, Carr, M.H., 1996, Water on Mars, Oxford University Press, New York, 197, Abundant water ice is also present beneath the permanent carbon dioxide ice cap at the Martian south pole and in the shallow subsurface at more temperate conditions.JOURNAL, Bibring, J.-P., Langevin, Yves, 2004, Perennial Water Ice Identified in the South Polar Cap of Mars, Nature, 428, 6983, 627–630, 10.1038/nature02461, 15024393, Poulet, François, Gendrin, Aline, Gondet, Brigitte, Berthé, Michel, Soufflot, Alain, Drossart, Pierre, Combes, Michel, Bellucci, Giancarlo, Moroz, Vassili, Mangold, Nicolas, Schmitt, Bernard, Omega Team, the, Erard, S., Forni, O., Manaud, N., Poulleau, G., Encrenaz, T., Fouchet, T., Melchiorri, R., Altieri, F., Formisano, V., Bonello, G., Fonti, S., Capaccioni, F., Cerroni, P., Coradini, A., Kottsov, V., Ignatiev, N., 2004Natur.428..627B, 29, JOURNAL, Pradeep, Thalappil, Kumar, Rajnish, Choudhary, Nilesh, Ragupathy, Gopi, Bhuin, Radha Gobinda, Methikkalam, Rabin Rajan J., Ghosh, Jyotirmoy, 2019-01-29, Clathrate hydrates in interstellar environment, Proceedings of the National Academy of Sciences, en, 116, 5, 1526–1531, 10.1073/pnas.1814293116, 0027-8424, 6358667, 30630945, NEWS, Water at Martian south pole, March 17, 2004, European Space Agency (ESA),weblink More than 21 million km3 of ice have been detected at or near the surface of Mars, enough to cover the whole planet to a depth of {{convert|35|meters}}. Even more ice is likely to be locked away in the deep subsurface.Carr, 2006, p. 173.Some liquid water may occur transiently on the Martian surface today, but limited to traces of dissolved moisture from the atmosphere and thin films, which are challenging environments for known life.WEB, Webster, Guy, Brown, Dwayne, NASA Mars Spacecraft Reveals a More Dynamic Red Planet,weblink December 10, 2013, NASA, NEWS,weblink Liquid Water From Ice and Salt on Mars, Geophysical Research Letters, NASA Astrobiology, July 3, 2014, August 13, 2014,weblink" title="">weblink August 14, 2014, yes, No large standing bodies of liquid water exist on the planet's surface, because the atmospheric pressure there averages just {{Convert|600|Pa|sp=us|lk=on}}, a figure slightly below the vapor pressure of water at its melting point; under average Martian conditions, pure water on the Martian surface would freeze or, if heated to above the melting point, would sublime to vapor. Before about 3.8 billion years ago, Mars may have had a denser atmosphere and higher surface temperatures,JOURNAL, Pollack, J.B., 1979, Climatic Change on the Terrestrial Planets, Icarus, 37, 3, 479–553, 10.1016/0019-1035(79)90012-5, 1979Icar...37..479P, JOURNAL, Pollack, J.B., Kasting, J.F., Richardson, S.M., Poliakoff, K., 1987, The Case for a Wet, Warm Climate on Early Mars, Icarus, 71, 2, 203–224, 10.1016/0019-1035(87)90147-3, 1987Icar...71..203P, 2060/19870013977, JOURNAL, Fairén, A. G., 2010, A cold and wet Mars Mars, Icarus, 208, 1, 165–175, 10.1016/j.icarus.2010.01.006, JOURNAL, Fairén, A. G., etal, 2009, Stability against freezing of aqueous solutions on early Mars, Nature, 459, 7245, 401–404, 10.1038/nature07978, 19458717, 2009Natur.459..401F, allowing vast amounts of liquid water on the surface,WEB,weblink releases/2015/03/150305140447,, May 25, 2015, JOURNAL, Villanueva, G., Mumma, M., Novak, R., Käufl, H., Hartogh, P., Encrenaz, T., Tokunaga, A., Khayat, A., Smith, M., 2015, Strong water isotopic anomalies in the martian atmosphere: Probing current and ancient reservoirs,weblink Science, 348, 6231, 218–221, 10.1126/science.aaa3630, 2015Sci...348..218V, 25745065, JOURNAL, Baker, V.R., Strom, R.G., Gulick, V.C., Kargel, J.S., Komatsu, G., Kale, V.S., 1991, Ancient oceans, ice sheets and the hydrological cycle on Mars, Nature, 352, 6348, 589–594, 10.1038/352589a0, 1991Natur.352..589B, JOURNAL, Salese, F., Ansan, V., Mangold, N., Carter, J., Anouck, O., Poulet, F., Ori, G.G., 2016, A sedimentary origin for intercrater plains north of the Hellas basin: Implications for climate conditions and erosion rates on early Mars, Journal of Geophysical Research: Planets, 121, 11, 2239–2267, 10.1002/2016JE005039, 2016JGRE..121.2239S, possibly including a large oceanJOURNAL, Parker, T.J., Saunders, R.S., Schneeberger, D.M., 1989, Transitional Morphology in West Deuteronilus Mensae, Mars: Implications for Modification of the Lowland/Upland Boundary, Icarus, 82, 1, 111–145, 10.1016/0019-1035(89)90027-4, 1989Icar...82..111P, JOURNAL, Dohm, J.M., Baker, Victor R., 2009, GRS Evidence and the Possibility of Paleooceans on Mars, Planetary and Space Science, 57, 5–6, 664–684, 10.1016/j.pss.2008.10.008, 2009P&SS...57..664D, Boynton, William V., Fairén, Alberto G., Ferris, Justin C., Finch, Michael, Furfaro, Roberto, Hare, Trent M., Janes, Daniel M., Kargel, Jeffrey S., Karunatillake, Suniti, Keller, John, Kerry, Kris, Kim, Kyeong J., Komatsu, Goro, Mahaney, William C., Schulze-Makuch, Dirk, Marinangeli, Lucia, Ori, Gian G., Ruiz, Javier, Wheelock, Shawn J.,weblink WEB,weblink PSRD: Ancient Floodwaters and Seas on Mars,, July 16, 2003, WEB,weblink Gamma-Ray Evidence Suggests Ancient Mars Had Oceans, SpaceRef, November 17, 2008, that may have covered one-third of the planet.JOURNAL, Clifford, S.M., Parker, T.J., 2001, The Evolution of the Martian Hydrosphere: Implications for the Fate of a Primordial Ocean and the Current State of the Northern Plains, Icarus, 154, 1, 40–79, 10.1006/icar.2001.6671, 2001Icar..154...40C, WEB,weblink Ancient ocean may have covered third of Mars,, June 14, 2010, Water has also apparently flowed across the surface for short periods at various intervals more recently in Mars' history.Carr, 2006, pp 144–147.JOURNAL, Fassett, C. I., Dickson, James L., 2010, Supraglacial and Proglacial Valleys on Amazonian Mars, Icarus, 208, 1, 86–100, 10.1016/j.icarus.2010.02.021, 2010Icar..208...86F, Head, James W., Levy, Joseph S., Marchant, David R., WEB,weblink Flashback: Water on Mars Announced 10 Years Ago,, June 22, 2000, On December 9, 2013, NASA reported that, based on evidence from the Curiosity rover studying Aeolis Palus, Gale Crater contained an ancient freshwater lake that could have been a hospitable environment for microbial life.NEWS, Chang, Kenneth, On Mars, an Ancient Lake and Perhaps Life,weblink December 9, 2013, New York Times, JOURNAL, Various, Science – Special Collection – Curiosity Rover on Mars,weblink December 9, 2013, Science (journal), Science, JOURNAL, Fairén, A. G., etal, 2014, A cold hydrological system in Gale crater, Mars, Planetary & Space Science, 93, 101–118, 10.1016/j.pss.2014.03.002, 2014P&SS...93..101F, Many lines of evidence indicate that water ice is abundant on Mars and it has played a significant role in the planet's geologic history.JOURNAL, Parker, T., 2000, Argyre Planitia and the Mars Global Hydrologic Cycle, XXXI, 2000LPI....31.2033P, Lunar and Planetary Science,weblink Clifford, S. M., Banerdt, W. B., 2033, JOURNAL, 10.1016/S0032-0633(02)00054-5, Heisinger, H., Head, J., 2002, Topography and morphology of the Argyre basin, Mars: implications for its geologic and hydrologic history, Planet. Space Sci., 50, 939–981, 2002P&SS...50..939H, 10–11, The present-day inventory of water on Mars can be estimated from spacecraft imagery, remote sensing techniques (spectroscopic measurements,BOOK, Soderblom, L.A., 1992, The composition and mineralogy of the Martian surface from spectroscopic observations – 0.3 micron to 50 microns, H.H., Kieffer, etal, University of Arizona Press, Tucson, AZ, 557–593, 978-0-8165-1257-7, JOURNAL, Glotch, T., P., Christensen, 2005, Geologic and mineralogical mapping of Aram Chaos: Evidence for water-rich history, J. Geophys. Res., 110, E9, E09006, 10.1029/2004JE002389, 2005JGRE..110.9006G, radar,JOURNAL, 2008LPI....39.2441H, 2008, Radar Sounding Evidence for Ice within Lobate Debris Aprons near Hellas Basin, Mid-Southern Latitudes of Mars, Lunar and Planetary Science, XXXIX, 1391,weblink Holt, J. W., Safaeinili, A., Plaut, J. J., Young, D. A., Head, J. W., Phillips, R. J., Campbell, B. A., Carter, L. M., Gim, Y., Seu, R., Sharad, Team, 2441, etc.), and surface investigations from landers and rovers.NEWS, Jonathan, Amos, Old Opportunity Mars rover makes rock discovery, June 10, 2013, BBC News,weblink NEWS, Mars Rover Opportunity Examines Clay Clues in Rock, May 17, 2013, Jet Propulsion Laboratory, NASA,weblink Geologic evidence of past water includes enormous outflow channels carved by floods,NEWS,weblink Regional, Not Global, Processes Led to Huge Martian Floods, Planetary Science Institute, SpaceRef, September 11, 2015, September 12, 2015, ancient river valley networks,JOURNAL, Harrison, K, Grimm, R., 2005, Groundwater-controlled valley networks and the decline of surface runoff on early Mars, Journal of Geophysical Research, 110, E12, E12S16, 10.1029/2005JE002455, 2005JGRE..11012S16H, JOURNAL, Howard, A., Moore, Jeffrey M., Irwin, Rossman P., 2005, An intense terminal epoch of widespread fluvial activity on early Mars: 1. Valley network incision and associated deposits, Journal of Geophysical Research, 110, E12, E12S14, 10.1029/2005JE002459, 2005JGRE..11012S14H, deltas,JOURNAL, Salese, F., Di Achille, G., Neesemann, A., Ori, G. G., Hauber, E., 2016, Hydrological and sedimentary analyses of well-preserved paleofluvial-paleolacustrine systems at Moa Valles, Mars, J. Geophys. Res. Planets, 121, 2, 194–232, 10.1002/2015JE004891, 2016JGRE..121..194S, and lakebeds;JOURNAL, 10.1016/j.icarus.2008.06.016, Fassett, C., Head, III, 2008, Valley network-fed, open-basin lakes on Mars: Distribution and implications for Noachian surface and subsurface hydrology, Icarus, 198, 1, 37–56, 2008Icar..198...37F, JOURNAL, 10.1006/icar.2001.6736, Moore, J., Wilhelms, D., 2001, Hellas as a possible site of ancient ice-covered lakes on Mars,weblink Icarus, 154, 258–276, 2001Icar..154..258M, 2, 2060/20020050249, JOURNAL, Weitz, C., T., Parker, 2000, New evidence that the Valles Marineris interior deposits formed in standing bodies of water, Lunar and Planetary Science, XXXI, 2000LPI....31.1693W,weblink 1693, and the detection of rocks and minerals on the surface that could only have formed in liquid water.WEB,weblink New Signs That Ancient Mars Was Wet,, October 28, 2008, Numerous geomorphic features suggest the presence of ground ice (permafrost)BOOK, Squyres, S.W., 1992, Ice in the Martian Regolith, Mars, H.H., Kieffer, etal, University of Arizona Press, Tucson, AZ, 523–554, 978-0-8165-1257-7, and the movement of ice in glaciers, both in the recent pastJOURNAL, Head, J., D., Marchant, 2006, Modifications of the walls of a Noachian crater in Northern Arabia Terra (24 E, 39 N) during northern mid-latitude Amazonian glacial epochs on Mars: Nature and evolution of Lobate Debris Aprons and their relationships to lineated valley fill and glacial systems (abstract), Lunar Planet. Sci., 37, 1128, JOURNAL, Head, J., etal, 2006, Modification if the dichotomy boundary on Mars by Amazonian mid-latitude regional glaciation, Geophys. Res. Lett., 33, 10.1029/2005gl024360, 2006GeoRL..33.8S03H, 33, 8, JOURNAL, Head, J., D., Marchant, 2006, Evidence for global-scale northern mid-latitude glaciation in the Amazonian period of Mars: Debris-covered glacial and valley glacial deposits in the 30 – 50 N latitude band (abstract), Lunar Planet. Sci., 37, 1127, WEB, Richard, Lewis,weblink Glaciers Reveal Martian Climate Has Been Recently Active, Brown University, April 23, 2008, and present.JOURNAL, Plaut, Jeffrey J., Safaeinili, Ali, Holt, John W., Phillips, Roger J., Head, James W., Seu, Roberto, Putzig, Nathaniel E., Frigeri, Alessandro, Radar Evidence for Ice in Lobate Debris Aprons in the Mid-Northern Latitudes of Mars, 10.1029/2008GL036379, 2009, 36, Geophysical Research Letters,weblink 2009GeoRL..3602203P, 2, n/a, Gullies and slope lineae along cliffs and crater walls suggest that flowing water continues to shape the surface of Mars, although to a far lesser degree than in the ancient past.Although the surface of Mars was periodically wet and could have been hospitable to microbial life billions of years ago,NEWS, Wall, Mike, Q & A with Mars Life-Seeker Chris Carr, March 25, 2011,weblink, the current environment at the surface is dry and subfreezing, probably presenting an insurmountable obstacle for living organisms. In addition, Mars lacks a thick atmosphere, ozone layer, and magnetic field, allowing solar and cosmic radiation to strike the surface unimpeded. The damaging effects of ionizing radiation on cellular structure is another one of the prime limiting factors on the survival of life on the surface.JOURNAL, Modelling the surface and subsurface Martian radiation environment: Implications for astrobiology, Geophysical Research Letters, January 30, 2007, L.R., Dartnell, Desorgher, Ward, Coates, 34, 2, L02207, 10.1029/2006GL027494, The damaging effect of ionising radiation on cellular structure is one of the prime limiting factors on the survival of life in potential astrobiological habitats., 2007GeoRL..34.2207D,weblink JOURNAL, Martian sub-surface ionising radiation: biosignatures and geology, Biogeosciences, 2007, L. R., Dartnell, L., Desorgher, J. M., Ward, A. J., Coates, 4, 4, 545–558, This ionising radiation field is deleterious to the survival of dormant cells or spores and the persistence of molecular biomarkers in the subsurface, and so its characterisation. [..] Even at a depth of 2 meters beneath the surface, any microbes would likely be dormant, cryopreserved by the current freezing conditions, and so metabolically inactive and unable to repair cellular degradation as it occurs., 2007BGeo....4..545D, 10.5194/bg-4-545-2007, Therefore, the best potential locations for discovering life on Mars may be in subsurface environments.JOURNAL, A Possible Biochemical Model for Mars, 43rd Lunar and Planetary Science Conference (2012), 2012, A., de Morais,weblink June 5, 2013, The extensive volcanism at that time much possibly created subsurface cracks and caves within different strata, and the liquid water could have been stored in these subterraneous places, forming large aquifers with deposits of saline liquid water, minerals organic molecules, and geothermal heat – ingredients for life as we know on Earth., NEWS, JohnThomas, Didymus, Scientists find evidence Mars subsurface could hold life, January 21, 2013,weblink Digital Journal – Science, There can be no life on the surface of Mars, because it is bathed in radiation and it's completely frozen. Life in the subsurface would be protected from that. – Prof. Parnell., NEWS, Bill, Steigerwald, Martian Methane Reveals the Red Planet is not a Dead Planet, January 15, 2009, NASA,weblink NASA's Goddard Space Flight Center, If microscopic Martian life is producing the methane, it likely resides far below the surface, where it's still warm enough for liquid water to exist, On November 22, 2016, NASA reported finding a large amount of underground ice on Mars; the volume of water detected is equivalent to the volume of water in Lake Superior. In July 2018, Italian scientists reported the discovery of a subglacial lake on Mars, {{convert|1.5|km|mi|abbr=on}} below the southern polar ice cap, and extending sideways about {{convert|20|km|mi|abbr=on}}, the first known stable body of water on the planet.NEWS, Halton, Mary, Liquid water 'lake' revealed on Mars,weblink July 26, 2018, BBC News, July 25, 2018, Understanding the extent and situation of water on Mars is vital to assess the planet’s potential for harboring life and for providing usable resources for future human exploration. For this reason, "Follow the Water" was the science theme of NASA's Mars Exploration Program (MEP) in the first decade of the 21st century. Discoveries by the 2001 Mars Odyssey, Mars Exploration Rovers (MERs), Mars Reconnaissance Orbiter (MRO), and Mars Phoenix lander have been instrumental in answering key questions about water's abundance and distribution on Mars. The ESA's Mars Express orbiter has also provided essential data in this quest.NASA Mars Exploration Program Overview.weblink The Mars Odyssey, Mars Express, MRO, and Mars Science Lander Curiosity rover are still sending back data from Mars, and discoveries continue to be made.

Historical background

The notion of water on Mars preceded the space age by hundreds of years. Early telescopic observers correctly assumed that the white polar caps and clouds were indications of water's presence. These observations, coupled with the fact that Mars has a 24-hour day, led astronomer William Herschel to declare in 1784 that Mars probably offered its inhabitants "a situation in many respects similar to ours."Sheehan, 1996, p. 35.{{multiple image| align = right| image1 = Karte Mars Schiaparelli MKL1888.png| width1 = 220| alt1 = | caption1 = Historical map of Mars from Giovanni Schiaparelli.| image2 = Lowell Mars channels.jpg| width2 = 220| alt2 = | caption2 = Mars canals illustrated by astronomer Percival Lowell, 1898.| footer = }}By the start of the 20th century, most astronomers recognized that Mars was far colder and drier than Earth. The presence of oceans was no longer accepted, so the paradigm changed to an image of Mars as a "dying" planet with only a meager amount of water. The dark areas, which could be seen to change seasonally, were then thought to be tracts of vegetation.BOOK, Kieffer, H.H., Jakosky, B.M, Snyder, C., 1992, The Planet Mars: From Antiquity to the Present, Mars, H.H., Kieffer, etal, University of Arizona Press, Tucson, AZ, 1–33, The man most responsible for popularizing this view of Mars was Percival Lowell (1855–1916), who imagined a race of Martians constructing a network of canals to bring water from the poles to the inhabitants at the equator. Although generating tremendous public enthusiasm, Lowell's ideas were rejected by most astronomers. The majority view of the scientific establishment at the time is probably best summarized by English astronomer Edward Walter Maunder (1851–1928) who compared the climate of Mars to conditions atop a twenty-thousand-foot peak on an arctic islandhartmann, 2003, p. 20. where only lichen might be expected to survive.In the meantime, many astronomers were refining the tool of planetary spectroscopy in hope of determining the composition of the Martian atmosphere. Between 1925 and 1943, Walter Adams and Theodore Dunham at the Mount Wilson Observatory tried to identify oxygen and water vapor in the Martian atmosphere, with generally negative results. The only component of the Martian atmosphere known for certain was carbon dioxide (CO2) identified spectroscopically by Gerard Kuiper in 1947.Sheehan, 1996, p. 150. Water vapor was not unequivocally detected on Mars until 1963.JOURNAL, Spinrad, H., Münch, G., Kaplan, L. D., 1963, Letter to the Editor: the Detection of Water Vapor on Mars, Astrophysical Journal, 137, 1319, 10.1086/147613, 1963ApJ...137.1319S, File:Mariner 4 craters.gif|thumb|left|Mariner 4Mariner 4The composition of the polar caps, assumed to be water ice since the time of Cassini (1666), was questioned by a few scientists in the late 1800s who favored CO2 ice, because of the planet's overall low temperature and apparent lack of appreciable water. This hypothesis was confirmed theoretically by Robert Leighton and Bruce Murray in 1966.JOURNAL, Leighton, R.B., Murray, B.C., 1966, Behavior of Carbon Dioxide and Other Volatiles on Mars, Science, 153, 3732, 136–144, 10.1126/science.153.3732.136, 17831495, 1966Sci...153..136L, Today it is known that the winter caps at both poles are primarily composed of CO2 ice, but that a permanent (or perennial) cap of water ice remains during the summer at the northern pole. At the southern pole, a small cap of CO2 ice remains during summer, but this cap too is underlain by water ice.The final piece of the Martian climate puzzle was provided by Mariner 4 in 1965. Grainy television pictures from the spacecraft showed a surface dominated by impact craters, which implied that the surface was very old and had not experienced the level of erosion and tectonic activity seen on Earth. Little erosion meant that liquid water had probably not played a large role in the planet's geomorphology for billions of years.JOURNAL, Leighton, R.B., Murray, B.C., Sharp, R.P., Allen, J.D., Sloan, R.K., 1965, Mariner IV Photography of Mars: Initial Results, Science, 149, 3684, 627–630, 10.1126/science.149.3684.627, 17747569, 1965Sci...149..627L, Furthermore, the variations in the radio signal from the spacecraft as it passed behind the planet allowed scientists to calculate the density of the atmosphere. The results showed an atmospheric pressure less than 1% of Earth's at sea level, effectively precluding the existence of liquid water, which would rapidly boil or freeze at such low pressures.JOURNAL, Kliore, A., etal, 1965, Occultation Experiment: Results of the First Direct Measurement of Mars's Atmosphere and Ionosphere, Science, 149, 3689, 1243–1248, 10.1126/science.149.3689.1243, 17747455, 1965Sci...149.1243K, Thus, a vision of Mars was born of a world much like the Moon, but with just a wisp of an atmosphere to blow the dust around. This view of Mars would last nearly another decade until Mariner 9 showed a much more dynamic Mars with hints that the planet’s past environment was more clement than the present one.On January 24, 2014, NASA reported that current studies on Mars by the Curiosity and Opportunity rovers will be searching for evidence of ancient life, including a biosphere based on autotrophic, chemotrophic and/or chemolithoautotrophic microorganisms, as well as ancient water, including fluvio-lacustrine environments (plains related to ancient rivers or lakes) that may have been habitable.JOURNAL, Grotzinger, John P., Introduction to Special Issue – Habitability, Taphonomy, and the Search for Organic Carbon on Mars, Science (journal), Science, January 24, 2014, 343, 6169, 386–387, 10.1126/science.1249944, 2014Sci...343..386G, 24458635, JOURNAL, Various, Special Issue – Table of Contents – Exploring Martian Habitability,weblink January 24, 2014, Science (journal), Science, 343, 6169, 345–452, JOURNAL, Grotzinger, J.P., etal, A Habitable Fluvio-Lacustrine Environment at Yellowknife Bay, Gale Crater, Mars, January 24, 2014, Science (journal), Science, 343, 6169, 10.1126/science.1242777, 1242777, 24324272, 2014Sci...343A.386G,, For many years it was thought that the observed remains of floods were caused by the release of water from a global water table, but research published in 2015 reveals regional deposits of sediment and ice emplaced 450 million years earlier to be the source.JOURNAL, Martian outflow channels: How did their source aquifers form, and why did they drain so rapidly?, Scientific Reports, September 8, 2015, Rodriguez, J. Alexis P., Kargel, Jeffrey S., Baker, Victor R., Gulick, Virginia C., 5, 10.1038/srep13404, 26346067, 4562069, etal, 13404, 2015NatSR...513404R, "Deposition of sediment from rivers and glacial melt filled giant canyons beneath primordial ocean contained within the planet's northern lowlands. It was the water preserved in these canyon sediments that was later released as great floods, the effects of which can be seen today."

Evidence from rocks and minerals

It is widely accepted that Mars had abundant water very early in its history,WEB, Staff, Ancient Mars Water Existed Deep Underground,weblink July 2, 2012,, JOURNAL, Craddock, R., Howard, A., 2002, The case for rainfall on a warm, wet early Mars, J. Geophys. Res., 107, E11, E11, 10.1029/2001je001505, 2002JGRE..107.5111C, but all large areas of liquid water have since disappeared. A fraction of this water is retained on modern Mars as both ice and locked into the structure of abundant water-rich materials, including clay minerals (phyllosilicates) and sulfates.JOURNAL, Head, J., etal, 2006, Extensive valley glacier deposits in the northern mid-latitudes of Mars: Evidence for the late Amazonian obliquity-driven climate change, Earth Planet. Sci. Lett., 241, 3–4, 663–671, 2006E&PSL.241..663H, 10.1016/j.epsl.2005.11.016, WEB, Staff, NASA, October 28, 2008,weblink NASA Mars Reconnaissance Orbiter Reveals Details of a Wetter Mars, SpaceRef, Studies of hydrogen isotopic ratios indicate that asteroids and comets from beyond 2.5 astronomical units (AU) provide the source of Mars' water,JOURNAL, The Origin of Water on Mars, Icarus, September 2003, Jonathan I., Lunine, John, Chambers, etal, 165, 1, 10.1016/S0019-1035(03)00172-6, 2003Icar..165....1L, 1–8, that currently totals 6% to 27% of the Earth's present ocean.(File:History of Water on Mars.jpg|left|thumb|History of water on Mars. Numbers represent how many billions of years ago)

Water in weathering products (aqueous minerals)

The primary rock type on the surface of Mars is basalt, a fine-grained igneous rock made up mostly of the mafic silicate minerals olivine, pyroxene, and plagioclase feldspar.BOOK, Soderblom, L.A., Bell, J.F., 2008, Exploration of the Martian Surface: 1992–2007, The Martian Surface: Composition, Mineralogy, and Physical Properties, J.F., Bell, Cambridge University Press, 3–19,, When exposed to water and atmospheric gases, these minerals chemically weather into new (secondary) minerals, some of which may incorporate water into their crystalline structures, either as H2O or as hydroxyl (OH). Examples of hydrated (or hydoxylated) minerals include the iron hydroxide goethite (a common component of terrestrial soils); the evaporate minerals gypsum and kieserite; opalline silica; and phyllosilicates (also called clay minerals), such as kaolinite and montmorillonite. All of these minerals have been detected on Mars.BOOK, Ming, D.W., Morris, R.V., Clark, R.C., 2008, Aqueous Alteration on Mars, The Martian Surface: Composition, Mineralogy, and Physical Properties, J.F., Bell, Cambridge University Press, 519–540,, One direct effect of chemical weathering is to consume water and other reactive chemical species, taking them from mobile reservoirs like the atmosphere and hydrosphere and sequestering them in rocks and minerals.BOOK, Lewis, J.S., 1997, Physics and Chemistry of the Solar System, revised, Academic Press, San Diego, CA, 978-0-12-446742-2, The amount of water in the Martian crust stored as hydrated minerals is currently unknown, but may be quite large.JOURNAL, Lasue, J., etal, 2013, Quantitative Assessments of the Martian Hydrosphere, Space Sci. Rev., 174, 1–4, 155–212, 10.1007/s11214-012-9946-5, 2013SSRv..174..155L, For example, mineralogical models of the rock outcroppings examined by instruments on the Opportunity rover at Meridiani Planum suggest that the sulfate deposits there could contain up to 22% water by weight.JOURNAL, Clark, B.C., etal, 2005, Chemistry and Mineralogy of Outcrops at Meridiani Planum, Earth Planet. Sci. Lett., 240, 1, 73–94, 10.1016/j.epsl.2005.09.040, 2005E&PSL.240...73C, On Earth, all chemical weathering reactions involve water to some degree.BOOK, Bloom, A.L., 1978, Geomorphology: A Systematic Analysis of Late Cenozoic Landforms, Prentice-Hall, Englewood Cliffs, N.J, 114, Thus, many secondary minerals do not actually incorporate water, but still require water to form. Some examples of anhydrous secondary minerals include many carbonates, some sulfates (e.g., anhydrite), and metallic oxides such as the iron oxide mineral hematite. On Mars, a few of these weathering products may theoretically form without water or with scant amounts present as ice or in thin molecular-scale films (monolayers).JOURNAL, Boynton, W.V., etal, 2009, Evidence for Calcium Carbonate at the Mars Phoenix Landing Site, Science, 325, 61–4, 10.1126/science.1172768, 19574384, 5936, 2009Sci...325...61B, BOOK, Gooding, J.L., Arvidson, R.E., Zolotov, M. YU., 1992, Physical and Chemical Weathering, Mars, H.H., Kieffer, etal, University of Arizona Press, Tucson, AZ, 626–651, 978-0-8165-1257-7, The extent to which such exotic weathering processes operate on Mars is still uncertain. Minerals that incorporate water or form in the presence of water are generally termed "aqueous minerals."Aqueous minerals are sensitive indicators of the type of environment that existed when the minerals formed. The ease with which aqueous reactions occur (see Gibbs free energy) depends on the pressure, temperature, and on the concentrations of the gaseous and soluble species involved.BOOK, Melosh, H.J., 2011, Planetary Surface Processes, Cambridge University Press, 978-0-521-51418-7, 296, Two important properties are pH and oxidation-reduction potential (Eh). For example, the sulfate mineral jarosite forms only in low pH (highly acidic) water. Phyllosilicates usually form in water of neutral to high pH (alkaline). Eh is a measure is the oxidation state of an aqueous system. Together Eh and pH indicate the types of minerals that are thermodynamically most likely to form from a given set of aqueous components. Thus, past environmental conditions on Mars, including those conducive to life, can be inferred from the types of minerals present in the rocks.

Hydrothermal alteration

Aqueous minerals can also form in the subsurface by hydrothermal fluids migrating through pores and fissures. The heat source driving a hydrothermal system may be nearby magma bodies or residual heat from large impacts.JOURNAL, Abramov, O., Kring, D.A., 2005, Impact-Induced Hydrothermal Activity on Early Mars, J. Geophys. Res., 110, E12, E12S09, 10.1029/2005JE002453, 2005JGRE..11012S09A, One important type of hydrothermal alteration in the Earth’s oceanic crust is serpentinization, which occurs when seawater migrates through ultramafic and basaltic rocks. The water-rock reactions result in the oxidation of ferrous iron in olivine and pyroxene to produce ferric iron (as the mineral magnetite) yielding molecular hydrogen (H2) as a byproduct. The process creates a highly alkaline and reducing (low Eh) environment favoring the formation of certain phyllosilicates (serpentine minerals) and various carbonate minerals, which together form a rock called serpentinite.JOURNAL, Schrenk, M.O., Brazelton, W.J., Lang, S.Q., 2013, Serpentinization, Carbon, and Deep Life, Reviews in Mineralogy & Geochemistry, 75, 1, 575–606, 10.2138/rmg.2013.75.18, 2013RvMG...75..575S, The hydrogen gas produced can be an important energy source for chemosynthtetic organisms or it can react with CO2 to produce methane gas, a process that has been considered as a non-biological source for the trace amounts of methane reported in the Martian atmosphere.JOURNAL, Baucom, Martin, Life on Mars?, American Scientist, March–April 2006,weblink Serpentine minerals can also store a lot of water (as hydroxyl) in their crystal structure. A recent study has argued that hypothetical serpentinites in the ancient highland crust of Mars could hold as much as a {{convert|500|m}}-thick global equivalent layer (GEL) of water.{{citation |last=Chassefière |first=E |last2=Langlais |first2=B |last3=Quesnel |first3=Y |last4=Leblanc |first4=F. |date=2013 |title=The Fate of Early Mars' Lost Water: The Role of Serpentinization |work=EPSC Abstracts |volume=8 |page=EPSC2013-188 |url= }} Although some serpentine minerals have been detected on Mars, no widespread outcroppings are evident from remote sensing data.JOURNAL, Ehlmann, B. L., Mustard, J.F., Murchie, S.L., 2010, Geologic Setting of Serpentine Deposits on Mars, Geophys. Res. Lett., 37, 6, L06201, 10.1029/2010GL042596, 2010GeoRL..37.6201E,weblink This fact does not preclude the presence of large amounts of sepentinite hidden at depth in the Martian crust.

Weathering rates

The rates at which primary minerals convert to secondary aqueous minerals vary. Primary silicate minerals crystallize from magma under pressures and temperatures vastly higher than conditions at the surface of a planet. When exposed to a surface environment these minerals are out of equilibrium and will tend to interact with available chemical components to form more stable mineral phases. In general, the silicate minerals that crystallize at the highest temperatures (solidify first in a cooling magma) weather the most rapidly.BOOK, Bloom, A.L., 1978, Geomorphology: A Systematic Analysis of Late Cenozoic Landforms, Prentice-Hall, Englewood Cliffs, N.J., ., p. 120 On Earth and Mars, the most common mineral to meet this criterion is olivine, which readily weathers to clay minerals in the presence of water.Olivine is widespread on Mars,JOURNAL, Ody, A., etal, 2013, Global Investigation of Olivine on Mars: Insights into Crust and Mantle Compositions, J. Geophys. Res., 118, 2, 234–262, 10.1029/2012JE004149, 2013JGRE..118..234O, suggesting that Mars' surface has not been pervasively altered by water; abundant geological evidence suggests otherwise.JOURNAL, Noble Gases in Iddingsite from the Lafayette meteorite: Evidence for Liquid water on Mars in the last few hundred million years, Meteoritics and Planetary Science, 35, 1, 107–115, 2000, 10.1111/j.1945-5100.2000.tb01978.x, Swindle, T. D., Treiman, A. H., Lindstrom, D. J., Burkland, M. K., Cohen, B. A., Grier, J. A., Li, B., Olson, E. K., 2000M&PS...35..107S, JOURNAL, Head, J., Kreslavsky, M. A., Ivanov, M. A., Hiesinger, H., Fuller, E. R., Pratt, S., 2001, Water in Middle Mars History: New Insights From MOLA Data, AGU Spring Meeting Abstracts, 2001, P31A–02 INVITED, 2001AGUSM...P31A02H, JOURNAL, Head, J., etal, 2001, Exploration for standing Bodies of Water on Mars: When Were They There, Where did They go, and What are the Implications for Astrobiology?, 2001AGUFM.P21C..03H, AGU Fall Meeting Abstracts, 21, P21C–03,

Martian meteorites

File:ALH84001.jpg|thumb|200px|Mars meteorite ALH84001ALH84001Over 60 meteorites have been found that came from Mars.Meyer, C. (2012) The Martian Meteorite Compendium; National Aronautics and Space Administration.weblink Some of them contain evidence that they were exposed to water when on Mars. Some Martian meteorites called basaltic shergottites, appear (from the presence of hydrated carbonates and sulfates) to have been exposed to liquid water prior to ejection into space.WEB,weblink Shergotty Meteorite – JPL, NASA, NASA, December 19, 2010, JOURNAL, Hamiliton, W., Christensen, Philip R., McSween, Harry Y., 1997, Determination of Martian meteorite lithologies and mineralogies using vibrational spectroscopy, Journal of Geophysical Research, 102, E11, 25593–25603, 10.1029/97JE01874, 1997JGR...10225593H, It has been shown that another class of meteorites, the nakhlites, were suffused with liquid water around 620 million years ago and that they were ejected from Mars around 10.75 million years ago by an asteroid impact. They fell to Earth within the last 10,000 years.JOURNAL,weblink Treiman, A., The nakhlite meteorites: Augite-rich igneous rocks from Mars, September 8, 2006, Chemie der Erde – Geochemistry, 65, 203–270, 2005, 10.1016/j.chemer.2005.01.004, 2005ChEG...65..203T, 3, Martian meteorite NWA 7034 has one order of magnitude more water than most other Martian meteorites. It is similar to the basalts studied by rover missions, and it was formed in the early Amazonian epoch.JOURNAL, Unique Meteorite from Early Amazonian Mars: Water-Rich Basaltic Breccia Northwest Africa 7034, Carl B., Agee, Nicole V., Wilson, Francis M., McCubbin, Karen, Ziegler, Victor J., Polyak, Zachary D., Sharp, Yemane, Asmerom, Morgan H., Nunn, Robina, Shaheen, Mark H., Thiemens, Andrew, Steele, Marilyn L., Fogel, Roxane, Bowden, Mihaela, Glamoclija, Zhisheng, Zhang, Stephen M., Elardo, February 15, 2013, Science, 339, 6121, 780–785, 10.1126/science.1228858, 23287721, 2013Sci...339..780A, Agree, C., et al. 2013. Unique Meteorite from Early Amazonian Mars: Water-Rich Basaltic Breccia Northwest Africa 7034. Science: 339, 780–785.In 1996, a group of scientists reported the possible presence of microfossils in the Allan Hills 84001, a meteorite from Mars.JOURNAL, 10.1126/science.273.5277.924, McKay, D., Gibson Jr., EK, Thomas-Keprta, KL, Vali, H, Romanek, CS, Clemett, SJ, Chillier, XD, Maechling, CR, Zare, RN, 1996, Search for Past Life on Mars: Possible Relic Biogenic Activity in Martian Meteorite AL84001, Science, 273, 5277, 924–930, 8688069, 1996Sci...273..924M, Many studies disputed the validity of the fossils.NEWS, Gibbs, W., C., Powell, Bugs in the Data?, August 19, 1996, Scientific American,weblink WEB,weblink Controversy Continues: Mars Meteorite Clings to Life – Or Does It?,, March 20, 2002, It was found that most of the organic matter in the meteorite was of terrestrial origin.JOURNAL, 10.1126/science.279.5349.362, Bada, J., Glavin, DP, McDonald, GD, Becker, L, 1998, A Search for Endogenous Amino Acids in Martian Meteorite AL84001, Science, 279, 5349, 362–365, 9430583, 1998Sci...279..362B, In addition, the scientific consensus is that "morphology alone cannot be used unambiguously as a tool for primitive life detection."JOURNAL, Morphological behavior of inorganic precipitation systems – Instruments, Methods, and Missions for Astrobiology II, SPIE Proceedings, December 30, 1999, Juan-Manuel Garcia-Ruiz, Proc. SPIE 3755, 74–82, 10.1117/12.375088, It is concluded that "morphology cannot be used unambiguously as a tool for primitive life detection.", Instruments, Methods, and Missions for Astrobiology II, Garcia-Ruiz, NEWS, Agresti, House, Jögi, Kudryavstev, McKeegan, Runnegar, Schopf, Wdowiak, Detection and geochemical characterization of Earth's earliest life, December 3, 2008, NASA,weblink NASA Astrobiology Institute, January 15, 2013, yes,weblink" title="">weblink January 23, 2013, JOURNAL, Evidence of Archean life: Stromatolites and microfossils, Precambrian Research, April 28, 2007, J. William, Schopf, Anatoliy B., Kudryavtsev, Andrew D., Czaja, Abhishek B., Tripathi, 158, 3–4, 141–155,weblink January 15, 2013, 10.1016/j.precamres.2007.04.009, 2007PreR..158..141S,weblink" title="">weblink December 24, 2012, yes, Interpretation of morphology is notoriously subjective, and its use alone has led to numerous errors of interpretation.

Geomorphic evidence

Lakes and river valleys

{{see also|Lakes on Mars}}The 1971 Mariner 9 spacecraft caused a revolution in our ideas about water on Mars. Huge river valleys were found in many areas. Images showed that floods of water broke through dams, carved deep valleys, eroded grooves into bedrock, and traveled thousands of kilometers. Areas of branched streams, in the southern hemisphere, suggested that rain once fell. The numbers of recognised valleys has increased through time. Research published in June 2010 mapped 40,000 river valleys on Mars, roughly quadrupling the number of river valleys that had previously been identified. Martian water-worn features can be classified into two distinct classes: 1) dendritic (branched), terrestrial-scale, widely distributed, Noachian-age valley networks and 2) exceptionally large, long, single-thread, isolated, Hesperian-age outflow channels. Recent work suggests that there may also be a class of currently enigmatic, smaller, younger (Hesperian to Amazonian) channels in the midlatitudes, perhaps associated with the occasional local melting of ice deposits.JOURNAL, Berman, Daniel C., Crown, David A., Bleamaster, Leslie F., 2009, 77–95, 200, 1, Icarus, Degradation of mid-latitude craters on Mars, 10.1016/j.icarus.2008.10.026, 2009Icar..200...77B, JOURNAL, Fassett, Caleb I., Head, James W., 2008, 61–89, 195, 1, Icarus, The timing of martian valley network activity: Constraints from buffered crater counting, 10.1016/j.icarus.2007.12.009, 2008Icar..195...61F, File:Kasei Valles topo.jpg|thumb|Kasei Valles—a major outflow channel—seen in MOLA elevation data. Flow was from bottom left to right. Image is approx. 1600 km across. The channel system extends another 1200 km south of this image to Echus ChasmaEchus ChasmaSome parts of Mars show inverted relief. This occurs when sediments are deposited on the floor of a stream and then become resistant to erosion, perhaps by cementation. Later the area may be buried. Eventually, erosion removes the covering layer and the former streams become visible since they are resistant to erosion. Mars Global Surveyor found several examples of this process.JOURNAL, Malin, Michael C., 2010, 1–60, 5, The Mars Journal, An overview of the 1985–2006 Mars Orbiter Camera science investigation, 10.1555/mars.2010.0001, 2010IJMSE...5....1M, WEB,weblink Sinuous Ridges Near Aeolis Mensae,, January 31, 2007, October 8, 2009,weblink" title="">weblink March 5, 2016, yes, Many inverted streams have been discovered in various regions of Mars, especially in the Medusae Fossae Formation,JOURNAL, 10.1016/j.icarus.2009.04.003, Zimbelman, J., Griffin, L., 2010, HiRISE images of yardangs and sinuous ridges in the lower member of the Medusae Fossae Formation, Mars, Icarus, 205, 1, 198–210, 2010Icar..205..198Z, Miyamoto Crater,JOURNAL, 10.1016/j.icarus.2009.03.030, Newsom, H., Lanza, Nina L., Ollila, Ann M., Wiseman, Sandra M., Roush, Ted L., Marzo, Giuseppe A., Tornabene, Livio L., Okubo, Chris H., Osterloo, Mikki M., Hamilton, Victoria E., Crumpler, Larry S., 2010, Inverted channel deposits on the floor of Miyamoto crater, Mars, Icarus, 205, 1, 64–72, 2010Icar..205...64N, Saheki Crater,JOURNAL, 10.1016/j.icarus.2013.11.007, Morgan, A.M., Howard, A.D., Hobley, D.E.J., Moore, J.M., Dietrich, W.E., Williams, R.M.E., Burr, D.M., Grant, J.A., Wilson, S.A., Matsubara, Y., 2014, Sedimentology and climatic environment of alluvial fans in the martian Saheki crater and a comparison with terrestrial fans in the Atacama Desert, Icarus, 229, 131–156, 2014Icar..229..131M,weblink and the Juventae Plateau.File:Antoniadi Crater Stream Channels.JPG|left|thumb|Inverted stream channels in Antoniadi Crater. Location is Syrtis Major quadrangleSyrtis Major quadrangleA variety of lake basins have been discovered on Mars. Some are comparable in size to the largest lakes on Earth, such as the Caspian Sea, Black Sea, and Lake Baikal. Lakes that were fed by valley networks are found in the southern highlands. There are places that are closed depressions with river valleys leading into them. These areas are thought to have once contained lakes; one is in Terra Sirenum that had its overflow move through Ma'adim Vallis into Gusev Crater, explored by the Mars Exploration Rover Spirit. Another is near Parana Valles and Loire Vallis.JOURNAL, 10.1006/icar.2000.6465, Goldspiel, J., Squires, S., 2000, Groundwater sapping and valley formation on Mars, Icarus, 148, 1, 176–192, 2000Icar..148..176G, Some lakes are thought to have formed by precipitation, while others were formed from groundwater. Lakes are estimated to have existed in the Argyre basin, the Hellas basin, and maybe in Valles Marineris.BOOK, The Surface of Mars, Cambridge Planetary Science Series (No. 6), 978-0-511-26688-1, Michael H., Carr, JOURNAL, 10.1016/0019-1035(87)90086-8, Nedell, S., Squyres, Steven W., Andersen, David W., 1987, Origin and evolution of the layered deposits in the Valles Marineris, Mars, Icarus, 70, 409–441, 1987Icar...70..409N, 3, It is likely that at times in the Noachian, many craters hosted lakes. These lakes are consistent with a cold, dry (by Earth standards) hydrological environment somewhat like that of the Great Basin of the western USA during the Last Glacial Maximum.Matsubara, Yo, Alan D. Howard, and Sarah A. Drummond. "Hydrology of early Mars: Lake basins." Journal of Geophysical Research: Planets 116.E4 (2011).Research from 2010 suggests that Mars also had lakes along parts of the equator. Although earlier research had showed that Mars had a warm and wet early history that has long since dried up, these lakes existed in the Hesperian Epoch, a much later period. Using detailed images from NASA's Mars Reconnaissance Orbiter, the researchers speculate that there may have been increased volcanic activity, meteorite impacts or shifts in Mars' orbit during this period to warm Mars' atmosphere enough to melt the abundant ice present in the ground. Volcanoes would have released gases that thickened the atmosphere for a temporary period, trapping more sunlight and making it warm enough for liquid water to exist. In this study, channels were discovered that connected lake basins near Ares Vallis. When one lake filled up, its waters overflowed the banks and carved the channels to a lower area where another lake would form.WEB,weblink Spectacular Mars images reveal evidence of ancient lakes,, January 4, 2010, February 28, 2018,weblink August 23, 2016, yes, JOURNAL, 10.1130/G30579.1, Gupta, Sanjeev, Warner, Nicholas, Kim, Rack, Lin, Yuan, Muller, Jan, -1#Jung-, Shih-, 2010, Hesperian equatorial thermokarst lakes in Ares Vallis as evidence for transient warm conditions on Mars, Geology, 38, 1, 71–74, 2010Geo....38...71W, These dry lakes would be targets to look for evidence (biosignatures) of past life.On September 27, 2012, NASA scientists announced that the Curiosity rover found direct evidence for an ancient streambed in Gale Crater, suggesting an ancient "vigorous flow" of water on Mars.NEWS, NASA Rover Finds Conditions Once Suited for Ancient Life on Mars, March 12, 2013,weblink NASA, In particular, analysis of the now dry streambed indicated that the water ran at {{convert|3.3|km/h|m/s|abbr=on}}, possibly at hip-depth. Proof of running water came in the form of rounded pebbles and gravel fragments that could have only been weathered by strong liquid currents. Their shape and orientation suggests long-distance transport from above the rim of the crater, where a channel named Peace Vallis feeds into the alluvial fan.Eridania Lake is a theorized ancient lake with a surface area of roughly 1.1 million square kilometers.Parker, T., D. Curie. 2001. Geomorphology 37. 303– Pablo, M., M. Druet. 2002. XXXIII LPSC. Abstract Pablo, M. 2003. VI Mars Conference, Abstract #3037. Its maximum depth is 2,400 meters and its volume is 562,000 km3. It was larger than the largest landlocked sea on Earth, the Caspian Sea and contained more water than all the other martian lakes together. The Eridania sea held more than 9 times as much water as all of North America's Great Lakes.WEB,weblink Mars Study Yields Clues to Possible Cradle of Life – Astrobiology Magazine, October 8, 2017,, WEB,weblink Mars' Eridania Basin Once Held Vast Sea - Planetary Science, Space Exploration -,, JOURNAL, Michalski, J., etal, 2017, Ancient hydrothermal seafloor deposits in Eridania basin on Mars, Nature Communications, 8, 15978, 2017NatCo...815978M, 10.1038/ncomms15978, 28691699, 5508135, The upper surface of the lake was assumed to be at the elevation of valley networks that surround the lake; they all end at the same elevation, suggesting that they emptied into a lake.Baker, D., J. Head. 2014. 44th LPSC, abstract #1252JOURNAL, Irwin, R., etal, 2004, Geomorphology of Ma'adim Vallis, Mars, and associated paleolake basins, J. Geophys. Res. Planets, 109, E12, E12009, 10.1029/2004je002287, 2004JGRE..10912009I, JOURNAL, Hynek, B., etal, 2010, Updated global map of Martian valley networks and implications for climate and hydrologic processes, J. Geophys. Res., 115, E9, E09008, 10.1029/2009je003548, 2010JGRE..115.9008H, Research with CRISM found thick deposits, greater than 400 meters thick, that contained the minerals saponite, talc-saponite, Fe-rich mica (for example, glauconite-nontronite), Fe- and Mg-serpentine, Mg-Fe-Ca-carbonate and probable Fe-sulphide. The Fe-sulphide probably formed in deep water from water heated by volcanoes. Such a process, classified as hydrothermal may have been a place where life on Earth began.PIA22059 fig1eridaniadepths.jpg|Map showing estimated water depth in different parts of Eridania Sea This map is about 530 miles across.PIA22058 hireseridanaregion.jpg|Deep-basin deposits from the floor of Eridania Sea. The mesas on the floor are there because they were protected against intense erosion by deep water/ice cover. CRISM measurements show minerals may be from seafloor hydrothermal deposits.PIA22060 hireseridania.jpg|Diagram showing how volcanic activity may have caused deposition of minerals on floor of Eridania Sea. Chlorides were deposited along the shoreline by evaporation.

Lake deltas

File:Distributary fan-delta.jpg|thumb|Delta in Eberswalde crater ]]Researchers have found a number of examples of deltas that formed in Martian lakes.JOURNAL, Di Achille, Gaetano, Hynek, Brian M., Ancient ocean on Mars supported by global distribution of deltas and valleys, Nature Geoscience, 3, 459–463, 2010, 10.1038/ngeo891, 2010NatGe...3..459D, 7, Finding deltas is a major sign that Mars once had a lot of liquid water. Deltas usually require deep water over a long period of time to form. Also, the water level needs to be stable to keep sediment from washing away. Deltas have been found over a wide geographical range, though there is some indication that deltas may be concentrated around the edges of the putative former northern ocean of Mars.JOURNAL, Di Achille, Gaetano, Hynek, Brian M., 2010, Ancient ocean on Mars supported by global distribution of deltas and valleys, Nature Geoscience, 3, 7, 459–463, 10.1038/ngeo891, 2010NatGe...3..459D,


File:Groundwaterseries8final.jpg|thumb|left|Layers may be formed by groundwater rising up gradually]]By 1979 it was thought that outflow channels formed in single, catastrophic ruptures of subsurface water reservoirs, possibly sealed by ice, discharging colossal quantities of water across an otherwise arid Mars surface.JOURNAL, Carr, M.H., 1979, Formation of Martian flood features by release of water from confined aquifers,weblink J. Geophys. Res., 84, 2995–3007, 1979JGR....84.2995C, 10.1029/JB084iB06p02995, JOURNAL, 10.1016/0019-1035(74)90101-8, Baker, V., Milton, D., 1974, Erosion by Catastrophic Floods on Mars and Earth, Icarus, 23, 1, 27–41, 1974Icar...23...27B, In addition, evidence in favor of heavy or even catastrophic flooding is found in the giant ripples in the Athabasca Vallis.WEB,weblink Mars Global Surveyor MOC2-862 Release,, January 16, 2012, JOURNAL, 10.1038/nature05594, Meridiani Planum and the global hydrology of Mars, 2007, Andrews-Hanna, Jeffrey C., Phillips, Roger J., Zuber, Maria T., Nature, 446, 7132, 163–6, 17344848, 2007Natur.446..163A, Many outflow channels begin at Chaos or Chasma features, providing evidence for the rupture that could have breached a subsurface ice seal.The branching valley networks of Mars are not consistent with formation by sudden catastrophic release of groundwater, both in terms of their dendritic shapes that do not come from a single outflow point, and in terms of the discharges that apparently flowed along them.JOURNAL, Irwin, Rossman, P., Robert A., Craddock, Alan D., Howard, Interior channels in Martian valley networks: Discharge and runoff production, Geology, 33, 6, 2005, 489–492, 10.1130/g21333.1, 2005Geo....33..489I, Instead, some authors have argued that they were formed by slow seepage of groundwater from the subsurface essentially as springs.JOURNAL, Jakosky, Bruce M., 1999, Water, Climate, and Life, Science, 283, 5402, 648–649, 10.1126/science.283.5402.648, 9988657, In support of this interpretation, the upstream ends of many valleys in such networks begin with box canyon or "amphitheater" heads, which on Earth are typically associated with groundwater seepage. There is also little evidence of finer scale channels or valleys at the tips of the channels, which some authors have interpreted as showing the flow appeared suddenly from the subsurface with appreciable discharge, rather than accumulating gradually across the surface. Others have disputed the link between amphitheater heads of valleys and formation by groundwater for terrestrial examples,Lamb, Michael P., et al. "Can springs cut canyons into rock?." Journal of Geophysical Research: Planets (1991–2012) 111.E7 (2006). and have argued that the lack of fine scale heads to valley networks is due to their removal by weathering or impact gardening. Most authors accept that most valley networks were at least partly influenced and shaped by groundwater seep processes.File:Burns cliff.jpg|thumb|right|The preservation and cementation of aeolian dune stratigraphy in Burns Cliff in Endurance Crater are thought to have been controlled by flow of shallow groundwater.JOURNAL, Grotzinger, J.P., R.E., Arvidson, J.F., Bell III, W., Calvin, B.C., Clark, D.A., Fike, M., Golombek, R., Greeley, A., Haldemann, K.E., Herkenhoff, B.L., Jolliff, A.H., Knoll, M., Malin, S.M., McLennan, T., Parker, L., Soderblom, J.N., Sohl-Dickstein, S.W., Squyres, N.J., Tosca, W.A., Watters, Stratigraphy and sedimentology of a dry to wet eolian depositional system, Burns formation, Meridiani Planum, Earth and Planetary Science Letters, 240, 1, November 25, 2005, 11–72, 0012-821X, 10.1016/j.epsl.2005.09.039, 2005E&PSL.240...11G, ]]Groundwater also played a vital role in controlling broad scale sedimentation patterns and processes on Mars.JOURNAL, Groundwater activity on Mars and implications for a deep biosphere, Nature Geoscience, January 20, 2013, Joseph R., Michalski, Paul B., Niles, Javier, Cuadros, John, Parnell, A. Deanne, Rogers, Shawn P., Wright, 6, 133–138, 10.1038/ngeo1706, Here we present a conceptual model of subsurface habitability of Mars and evaluate evidence for groundwater upwelling in deep basins., 2013NatGe...6..133M, 2, According to this hypothesis, groundwater with dissolved minerals came to the surface, in and around craters, and helped to form layers by adding minerals —especially sulfate— and cementing sediments.JOURNAL, Andrews‐Hanna, J. C., M. T., Zuber, R. E., Arvidson, S. M., Wiseman, 2010, Early Mars hydrology: Meridiani playa deposits and the sedimentary record of Arabia Terra, J. Geophys. Res., 115, E6, E06002, 10.1029/2009JE003485, 2010JGRE..115.6002A, JOURNAL, McLennan, S. M., etal, 2005, Provenance and diagenesis of the evaporitebearing Burns formation, Meridiani Planum, Mars, Earth Planet. Sci. Lett., 240, 1, 95–121, 10.1016/j.epsl.2005.09.041, 2005E&PSL.240...95M, JOURNAL, Squyres, S. W., A. H., Knoll, 2005, Sedimentary rocks at Meridiani Planum: Origin, diagenesis, and implications for life on Mars, Earth Planet. Sci. Lett., 240, 1, 1–10, 10.1016/j.epsl.2005.09.038, 2005E&PSL.240....1S, .JOURNAL, Squyres, S. W., etal, 2006, Two years at Meridiani Planum: Results from the Opportunity rover, Science, 313, 5792, 1403–1407, 10.1126/science,weblink 2006Sci...313.1403S, . In other words, some layers may have been formed by groundwater rising up depositing minerals and cementing existing, loose, aeolian sediments. The hardened layers are consequently more protected from erosion. A study published in 2011 using data from the Mars Reconnaissance Orbiter, show that the same kinds of sediments exist in a large area that includes Arabia Terra.CONFERENCE, M., Wiseman, J. C., Andrews-Hanna, R. E., Arvidson, J. F., Mustard, K. J., Zabrusky, Distribution of Hydrated Sulfates Across Arabia Terra Using CRISM Data: Implications for Martian Hydrology,weblink 42nd Lunar and Planetary Science Conference, 2011, It has been argued that areas that are rich in sedimentary rocks are also those areas that most likely experienced groundwater upwelling on a regional scale.JOURNAL, Andrews‐Hanna, Jeffrey C., Kevin W., Lewis, Early Mars hydrology: 2. Hydrological evolution in the Noachian and Hesperian epochs, Journal of Geophysical Research: Planets, 116, E2, E2, 2011, 10.1029/2010je003709, 2011JGRE..116.2007A, In February 2019, European scientists published geological evidence of an ancient planet-wide groundwater system that was, arguably, connected to a putative vast ocean.NEWS, ESA Staff, First Evidence of "Planet-Wide Groundwater System" on Mars Found,weblink 28 February 2019, European Space Agency, 28 February 2019, NEWS, Houser, Kristin, First Evidence of "Planet-Wide Groundwater System" on Mars Found,weblink 28 February 2019,, 28 February 2019, JOURNAL, 10.1029/2018JE005802, 31007995, 6472477, Geological Evidence of Planet-Wide Groundwater System on Mars, Journal of Geophysical Research: Planets, 124, 2, 374–395, 2019, Salese, Francesco, Pondrelli, Monica, Neeseman, Alicia, Schmidt, Gene, Ori, Gian Gabriele, 2019JGRE..124..374S, WEB,weblink Mars: Planet‐Wide Groundwater System – New Geological Evidence, February 19, 2019,

Mars ocean hypothesis

missing image!
- MarsTopoMap-PIA02031 modest.jpg -
The blue region of low topography in the Martian northern hemisphere is hypothesized to be the site of a primordial ocean of liquid water.{{citation |first=John E. |last=Brandenburg |contribution=The Paleo-Ocean of Mars |title=MECA Symposium on Mars: Evolution of its Climate and Atmosphere |publisher=Lunar and Planetary Institute |pages=20–22 |date=1987 |id=|bibcode=1987meca.symp...20B
European Space AgencyThe Mars ocean hypothesis proposes that the Vastitas Borealis basin was the site of an ocean of liquid water at least once, and presents evidence that nearly a third of the surface of Mars was covered by a liquid ocean early in the planet's geologic history.JOURNAL, 10.1006/icar.2001.6671, Clifford, S. M., Parker, T. J., 2001, The Evolution of the Martian Hydrosphere: Implications for the Fate of a Primordial Ocean and the Current State of the Northern Plains, Icarus, 154, 40–79, 2001Icar..154...40C, This ocean, dubbed Oceanus Borealis, would have filled the Vastitas Borealis basin in the northern hemisphere, a region that lies {{convert|4-5|km}} below the mean planetary elevation. Two major putative shorelines have been suggested: a higher one, dating to a time period of approximately 3.8 billion years ago and concurrent with the formation of the valley networks in the Highlands, and a lower one, perhaps correlated with the younger outflow channels. The higher one, the 'Arabia shoreline', can be traced all around Mars except through the Tharsis volcanic region. The lower, the 'Deuteronilus', follows the Vastitas Borealis formation.A study in June 2010 concluded that the more ancient ocean would have covered 36% of Mars. Data from the Mars Orbiter Laser Altimeter (MOLA), which measures the altitude of all terrain on Mars, was used in 1999 to determine that the watershed for such an ocean would have covered about 75% of the planet.JOURNAL, Smith, D., etal, 1999, The Gravity Field of Mars: Results from Mars Global Surveyor, Science, 286, 5437, 94–97, 10.1126/science.286.5437.94, 1999Sci...286...94S,weblink 10506567, Early Mars would have required a warmer climate and denser atmosphere to allow liquid water to exist at the surface.BOOK, 978-3-540-40743-0, Read, Peter L., S. R., Lewis, The Martian Climate Revisited: Atmosphere and Environment of a Desert Planet, Praxis, Chichester, UK, 2004,weblink Paperback, December 19, 2010, WEB,weblink Martian North Once Covered by Ocean,, December 19, 2010, November 26, 2009, In addition, the large number of valley networks strongly supports the possibility of a hydrological cycle on the planet in the past.JOURNAL, 10.1038/447785a, Zuber, Maria T., 2007, Planetary Science: Mars at the tipping point, Nature, 447, 7146, 785–786, 17568733, 2007Natur.447..785Z, WEB,weblink New Map Bolsters Case for Ancient Ocean on Mars,, November 23, 2009, The existence of a primordial Martian ocean remains controversial among scientists, and the interpretations of some features as 'ancient shorelines' has been challenged.JOURNAL, Carr, M., Head, J., 2003, Oceans on Mars: An assessment of the observational evidence and possible fate, Journal of Geophysical Research, 108, E5, 5042, 2003JGRE..108.5042C, 10.1029/2002JE001963, WEB,weblink Mars Ocean Hypothesis Hits the Shore, NASA Astrobiology, NASA, January 26, 2001, yes,weblink" title="">weblink February 20, 2012, One problem with the conjectured 2-billion-year-old (2 Ga) shoreline is that it is not flat—i.e., does not follow a line of constant gravitational potential. This could be due to a change in distribution in Mars' mass, perhaps due to volcanic eruption or meteor impact;JOURNAL, Perron, J., Taylor, etal, Evidence for an ancient Martian ocean in the topography of deformed shorelines, Nature, 447, 7146, 2007, 840–843, 10.1038/nature05873, 17568743, 2007Natur.447..840P, the Elysium volcanic province or the massive Utopia basin that is buried beneath the northern plains have been put forward as the most likely causes.In March 2015, scientists stated that evidence exists for an ancient Martian ocean, likely in the planet's northern hemisphere and about the size of Earth's Arctic Ocean, or approximately 19% of the Martian surface. This finding was derived from the ratio of water and deuterium in the modern Martian atmosphere compared to the ratio found on Earth. Eight times as much deuterium was found at Mars than exists on Earth, suggesting that ancient Mars had significantly higher levels of water. Results from the Curiosity rover had previously found a high ratio of deuterium in Gale Crater, though not significantly high enough to suggest the presence of an ocean. Other scientists caution that this new study has not been confirmed, and point out that Martian climate models have not yet shown that the planet was warm enough in the past to support bodies of liquid water.NEWS,weblink Mars Had an Ocean, Scientists Say, Pointing to New Data, The New York Times, Kaufman, Marc, March 5, 2015, March 5, 2015, Additional evidence for a northern ocean was published in May 2016, describing how some of the surface in Ismenius Lacus quadrangle was altered by two tsunamis. The tsunamis were caused by asteroids striking the ocean. Both were thought to have been strong enough to create 30 km diameter craters. The first tsunami picked up and carried boulders the size of cars or small houses. The backwash from the wave formed channels by rearranging the boulders. The second came in when the ocean was 300 m lower. The second carried a great deal of ice which was dropped in valleys. Calculations show that the average height of the waves would have been 50 m, but the heights would vary from 10 m to 120 m. Numerical simulations show that in this particular part of the ocean two impact craters of the size of 30 km in diameter would form every 30 million years. The implication here is that a great northern ocean may have existed for millions of years. One argument against an ocean has been the lack of shoreline features. These features may have been washed away by these tsunami events. The parts of Mars studied in this research are Chryse Planitia and northwestern Arabia Terra. These tsunamis affected some surfaces in the Ismenius Lacus quadrangle and in the Mare Acidalium quadrangle.WEB,weblink Ancient Tsunami Evidence on Mars Reveals Life Potential – Astrobiology,, Rodriguez, J., et al. 2016. Tsunami waves extensively resurfaced the shorelines of an early Martian ocean. Scientific Reports: 6, 25106.JOURNAL, Tsunami waves extensively resurfaced the shorelines of an early Martian ocean, J. Alexis P., Rodriguez, Alberto G., Fairén, Kenneth L., Tanaka, Mario, Zarroca, Rogelio, Linares, Thomas, Platz, Goro, Komatsu, Hideaki, Miyamoto, Jeffrey S., Kargel, Jianguo, Yan, Virginia, Gulick, Kana, Higuchi, Victor R., Baker, Natalie, Glines, May 19, 2016, Scientific Reports, 6, 1, 25106, 10.1038/srep25106, 27196957, 4872529, 2016NatSR...625106R, Cornell University. "Ancient tsunami evidence on Mars reveals life potential." ScienceDaily. ScienceDaily, May 19, 2016. .In July 2019, support was reported for an ancient ocean on Mars that may have been formed by a possible mega-tsunami source resulting from a meteorite impact creating Lomonosov crater.NEWS, Andrews, Robin George, When a Mega-Tsunami Drowned Mars, This Spot May Have Been Ground Zero - The 75-mile-wide crater could be something like a Chicxulub crater for the red planet.,weblink July 30, 2019, The New York Times, July 31, 2019, JOURNAL, Costard, F., et al., The Lomonosov Crater Impact Event: A Possible Mega‐Tsunami Source on Mars, June 26, 2019, (Journal of Geophysical Research: Planets), 124, 7, 1840, 10.1029/2019JE006008, 2019JGRE..124.1840C,

Present water

{{multiple image
|image1=Water equivalent hydrogen abundance in the lower latitudes of Mars 01.jpg
|image2=Water equivalent hydrogen abundance in the high latitudes of Mars.jpg
|caption2=Proportion of water ice present in the upper meter of the Martian surface for lower (top) and higher (bottom) latitudes. The percentages are derived through stoichiometric calculations based on epithermal neutron fluxes. These fluxes were detected by the Neutron Spectrometer aboard the 2001 Mars Odyssey spacecraft.}}
A significant amount of surface hydrogen has been observed globally by the Mars Odyssey neutron spectrometer and gamma ray spectrometer.JOURNAL, Boynton, W. V., etal, 2007, Concentration of H, Si, Cl, K, Fe, and Th in the low and mid latitude regions of Mars, (Journal of Geophysical Research: Planets), 112, E12, E12S99, 10.1029/2007JE002887, 2007JGRE..11212S99B, This hydrogen is thought to be incorporated into the molecular structure of ice, and through stoichiometric calculations the observed fluxes have been converted into concentrations of water ice in the upper meter of the Martian surface. This process has revealed that ice is both widespread and abundant on the present surface. Below 60 degrees of latitude, ice is concentrated in several regions, particularly around the Elysium volcanoes, Terra Sabaea, and northwest of Terra Sirenum, and exists in concentrations up to 18% ice in the subsurface. Above 60 degrees latitude, ice is highly abundant. Polewards on 70 degrees of latitude, ice concentrations exceed 25% almost everywhere, and approach 100% at the poles.JOURNAL, Feldman, W. C., Prettyman, T. H., Maurice, S., Plaut, J. J., Bish, D. L., Vaniman, D. T., Tokar, R. L., 2004, Global distribution of near-surface hydrogen on Mars, Journal of Geophysical Research, 109, E9, E9, E09006, 10.1029/2003JE002160, 2004JGRE..109.9006F, The SHARAD and MARSIS radar sounding instruments have also confirmed that individual surface features are ice rich. Due to the known instability of ice at current Martian surface conditions, it is thought that almost all of this ice is covered by a thin layer of rocky or dusty material.The Mars Odyssey neutron spectrometer observations indicate that if all the ice in the top meter of the Martian surface were spread evenly, it would give a Water Equivalent Global layer (WEG) of at least ≈{{convert|14|cm}}—in other words, the globally averaged Martian surface is approximately 14% water.JOURNAL, Feldman, W. C., etal, 2004, Global distribution of near-surface hydrogen on Mars, Journal of Geophysical Research, 10.1029/2003JE002160, 2004JGRE..109.9006F, 109, E9, The water ice currently locked in both Martian poles corresponds to a WEG of {{convert|30|m}}, and geomorphic evidence favors significantly larger quantities of surface water over geologic history, with WEG as deep as {{convert|500|m}}.JOURNAL, Christensen, P. R., 2006, Water at the Poles and in Permafrost Regions of Mars, GeoScienceWorld Elements, 2, 3, 151–155, It is thought that part of this past water has been lost to the deep subsurface, and part to space, although the detailed mass balance of these processes remains poorly understood. The current atmospheric reservoir of water is important as a conduit allowing gradual migration of ice from one part of the surface to another on both seasonal and longer timescales, but it is insignificant in volume, with a WEG of no more than {{convert|10|µm}}.

Polar ice caps

File:Martian north polar cap.jpg|thumb|The Mars Global SurveyorMars Global SurveyorFile:Perspective view of Korolev crater.jpg|thumb|Korolev CraterKorolev CraterBoth the northern polar cap (Planum Boreum) and the southern polar cap (Planum Australe) have been observed to grow in thickness during the winter and partially sublime during the summer. In 2004, the MARSIS radar sounder on the Mars Express satellite targeted the southern polar cap, and was able to confirm that ice there extends to a depth of {{convert|3.7|km|mi}} below the surface. In the same year, the OMEGA instrument on the same orbiter revealed that the cap is divided into three distinct parts, with varying contents of frozen water depending on latitude. The first part is the bright part of the polar cap seen in images, centered on the pole, which is a mixture of 85% CO2 ice to 15% water ice. The second part comprises steep slopes known as scarps, made almost entirely of water ice, that ring and fall away from the polar cap to the surrounding plains. The third part encompasses the vast permafrost fields that stretch for tens of kilometres away from the scarps, and is not obviously part of the cap until the surface composition is analysed. NASA scientists calculate that the volume of water ice in the south polar ice cap, if melted, would be sufficient to cover the entire planetary surface to a depth of {{convert|11|m|ft|sp=us}}.WEB, NASA, March 15, 2007, Mars' South Pole Ice Deep and Wide, NASA News & Media Resources,weblink JOURNAL, Plaut, J. J., etal, Subsurface Radar Sounding of the South Polar Layered Deposits of Mars, Science, March 15, 2007, 10.1126/science.1139672, 316, 5821, 92–95, 17363628, 2007Sci...316...92P, (File:PIA13164 North Polar Cap Cross Section, Annotated Version.jpg|thumb|left|Cross-section of a portion of the north polar ice cap of Mars, derived from satellite radar sounding.)An ancient ice sheet that has been proposed for the south polar region may have contained 20 million km3 of water ice, which is equivalent to a layer 137 m deep over the entire planet.Scanlon, K., et al. 2018. The Dorsa Argentea Formation and the Noachian-Hesperian climate transition. Icarus: 299, 339–363.Head, J, S. Pratt. 2001. Extensive Hesperian-aged south polar ice sheet on Mars: Evidence for massive melting and retreat, and lateral flow and pending of meltwater. J. Geophys. Res.-Planet, 106 (E6), 12275-12299.In July 2008, NASA announced that the Phoenix lander had confirmed the presence of water ice at its landing site near the northern polar ice cap (at 68.2° latitude). This was the first ever direct observation of ice from the surface. Two years later, the shallow radar on board the Mars Reconnaissance Orbiter took measurements of the north polar ice cap and determined that the total volume of water ice in the cap is {{convert|821000|km³}}. That is equal to 30% of the Earth's Greenland ice sheet, or enough to cover the surface of Mars to a depth of {{convert|5.6|m}}.WEB,weblink Radar Map of Buried Mars Layers Matches Climate Cycles, OnOrbit, December 19, 2010, yes,weblink" title="">weblink December 21, 2010, Both polar caps reveal abundant fine internal layers when examined in HiRISE and Mars Global Surveyor imagery. Many researchers have studied this layering to understand the structure, history, and flow properties of the caps, although their interpretation is not straightforward.JOURNAL, KE, Fishbaugh, Byrne, 2010, Shane, Herkenhoff, Kenneth E., Kirk, Randolph L., Fortezzo, Corey, Russell, Patrick S., McEwen, Alfred, Evaluating the meaning of "layer" in the Martian north polar layered depsoits and the impact on the climate connection, Icarus, 205, 1, 269–282, 10.1016/j.icarus.2009.04.011, 2010Icar..205..269F,weblink Near the northern polar cap is the {{convert|81.4|km|mi}} wide Korolev Crater, where the Mars Express orbiter found it to be filled with approximately {{convert|2200|km3|mi3}} of water ice.WEB, A winter wonderland in red and white – Korolev Crater on Mars,weblink German Aerospace Center (DLR), 20 December 2018, The crater floor lies about {{convert|2|km|mi}} below the rim, and is covered by a {{convert|1.8|km|mi}} deep central mound of permanent water ice, up to {{convert|60|km|mi}} in diameter.NEWS,weblink The Guardian, December 21, 2018, Mars Express beams back images of ice-filled Korolev crater, December 21, 2018, Editor, Ian Sample Science,

{{anchor|Subglacial liquid water}}Subglacial liquid water

File:Mars-SubglacialWater-SouthPoleRegion-20180725.jpg|thumb|Site of south polar subglacial water body (reported July 2018)]]Lake Vostok in Antarctica may have implications for liquid water still existing on Mars, because if water existed before the polar ice caps on Mars, so it is thought possible that there is still liquid water below the ice caps.JOURNAL,weblink Duxbury, N. S., Zotikov, I. A., Nealson, K. H., Romanovsky, V. E., Carsey, F. D., A numerical model for an alternative origin of Lake Vostok and its exobiological implications for Mars, 10.1029/2000JE001254, 2001, 1453, 106, E1, Journal of Geophysical Research, 2001JGR...106.1453D, Then in July 2018, scientists from the Italian Space Agency reported the detection of a subglacial lake on Mars, {{convert|1.5|km|0}} below the southern polar ice cap, and spanning {{convert|20|km|-1}} horizontally, the first evidence for a stable body of liquid water on the planet.JOURNAL, Orosei, R., etal, Radar evidence of subglacial liquid water on Mars, July 25, 2018, Science (journal), Science, 361, 6401, 490–493, 10.1126/science.aar7268, 30045881, 2018Sci...361..490O, 11573/1148029, NEWS, Chang, Kenneth, Overbye, Dennis, Dennis Overbye, A Watery Lake Is Detected on Mars, Raising the Potential for Alien Life – The discovery suggests that watery conditions beneath the icy southern polar cap may have provided one of the critical building blocks for life on the red planet.,weblink July 25, 2018, The New York Times, July 25, 2018, WEB, Huge reservoir of liquid water detected under the surface of Mars,weblink EurekAlert, July 25, 2018, July 25, 2018, WEB, Liquid water 'lake' revealed on Mars,weblink BBC News, July 25, 2018, July 25, 2018, The evidence for the Mars lake was deduced from a bright spot in the radar echo sounding data, collected between May 2012 and December 2015, using the MARSIS radar on board the European Mars Express orbiter.Supplementary Materials for: Radar evidence of subglacial liquid water on Mars. (PDF). R. Orosei, S. E. Lauro, E. Pettinelli, A. Cicchetti, M. Coradini, B. Cosciotti, F. Di Paolo, E. Flamini, E. Mattei, M. Pajola, F. Soldovieri, M. Cartacci, F. Cassenti, A. Frigeri, S. Giuppi, R. Martufi, A. Masdea, G. Mitri, C. Nenna, R. Noschese, M. Restano, R. Seu. Science. July 25, 2018 {{doi|10.1126/science.aar7268}} The detected lake is centered at 193°E, 81°S, a flat area that does not exhibit any peculiar topographic characteristics but is surrounded by higher ground, except on its eastern side, where there is a depression. The SHARAD radar on board NASA's Mars Reconnaissance Orbiter has seen no sign of the lake, but the team will take another look to try to confirm the finding when its orbital parameters are favorable.Mars (probably) has a lake of liquid water. Lisa Grossman, Science News. July 25, 2018. It is unlikely that SHARAD will detect the lake, as it has much lower ground-penetrating abilities than MARSIS does.Because the temperature at the base of the polar cap is estimated at {{convert|205|K}}, scientists assume that the water may remain liquid by the antifreeze effect of magnesium and calcium perchlorates.WEB,weblink Liquid water 'lake' revealed on Mars, Mary, Halton, BBC News, July 25, 2018, The {{convert|1.5|km|adj=on}} ice layer covering the lake is composed of water ice with 10 to 20% admixed dust, and seasonally covered by a {{convert|1|m|adj=on}}-thick layer of {{CO2}} ice. Since the raw-data coverage of the south polar ice cap is limited, the discoverers stated that "there is no reason to conclude that the presence of subsurface water on Mars is limited to a single location."The lake may consist of clear water, or may be mixed with soil to form a sludge.NEWS, Giant liquid water lake found under Martian ice,weblink July 25, 2018, July 26, 2018, RTÉ, The lake's high levels of salt would present difficulties for most lifeforms, but on Earth, organisms called halophiles thrive in salty conditions, though not in dark, cold, concentrated perchlorate solutions.

Ground ice

For many years, various scientists have suggested that some Martian surfaces look like periglacial regions on Earth. By analogy with these terrestrial features, it has been argued for many years that these may be regions of permafrost. This would suggest that frozen water lies right beneath the surface.JOURNAL, Wilson, Jack T., etal, Equatorial locations of water on Mars: Improved resolution maps based on Mars Odyssey Neutron Spectrometer data, January 2018, Icarus (journal), Icarus, 10.1016/j.icarus.2017.07.028, 2018Icar..299..148W, 299, 148–160, 1708.00518, WEB, Howell, Elizabeth, Water Ice Mystery Found at Martian Equator,weblink October 2, 2017,, October 2, 2017, A common feature in the higher latitudes, patterned ground, can occur in a number of shapes, including stripes and polygons. On the Earth, these shapes are caused by the freezing and thawing of soil.WEB,weblink Polygonal Patterned Ground: Surface Similarities Between Mars and Earth, SpaceRef, September 28, 2002, There are other types of evidence for large amounts of frozen water under the surface of Mars, such as terrain softening, which rounds sharp topographical features.JOURNAL, 10.1016/0019-1035(89)90078-X, Squyres, S., 1989, Urey Prize Lecture: Water on Mars, Icarus, 79, 229–288, 1989Icar...79..229S, 2, Evidence from Mars Odyssey's gamma ray spectrometer and direct measurements with the Phoenix lander have corroborated that many of these features are intimately associated with the presence of ground ice.JOURNAL, 10.1016/j.icarus.2009.06.005, Lefort, A., Russell, 2010, P.S., Thomas, N., Scaloped terrains in the Peneus and Amphitrites Paterae region of Mars as observed by HiRISE, Icarus, 205, 1, 259–268, 2010Icar..205..259L, File:Mars exposed subsurface ice.jpg|thumb|A cross-section of underground water ice is exposed at the steep slope that appears bright blue in this enhanced-color view from the (Mars Reconnaissance Orbiter|MRO]]. The scene is about 500 meters wide. The scarp drops about 128 meters from the level ground. The ice sheets extend from just below the surface to a depth of 100 meters or more.Exposed subsurface ice sheets in the Martian mid-latitudes. Colin M. Dundas, et al. Science, January 12, 2018. Vol. 359, Issue 6372, pp. 199–201. {{doi|10.1126/science.aao1619}})Using the HiRISE camera on board the Mars Reconnaissance Orbiter (MRO), researchers found in 2017 at least eight eroding slopes showing exposed water ice sheets as thick as 100 meters, covered by a layer of about 1 or 2 meters thick of soil.Steep Slopes on Mars Reveal Structure of Buried Ice. NASA Press Release. January 11, 2018.Ice cliffs spotted on Mars. Science News. Paul Voosen. January 11, 2018. The sites are at latitudes from about 55 to 58 degrees, suggesting that there is shallow ground ice under roughly a third of the Martian surface. This image confirms what was previously detected with the spectrometer on 2001 Mars Odyssey, the ground-penetrating radars on MRO and on Mars Express, and by the Phoenix lander in situ excavation. These ice layers hold easily accessible clues about Mars' climate history and make frozen water accessible to future robotic or human explorers. Some researchers suggested these deposits could be the remnants of glaciers that existed millions of years ago when the planet's spin axis and orbit were different. (See section Mars' Ice ages below.)File:50345 1230icelayersangular.jpg|Close view of wall of triangular depression, as seen by HiRISE layers are visible in the wall. These layers contain ice. The lower layers are tilted, while layers near the surface are more or less horizontal. Such an arrangement of layers is called an "angular unconformity."Supplementary Materials Exposed subsurface ice sheets in the Martian mid-latitudes Colin M. Dundas, Ali M. Bramson, Lujendra Ojha, James J. Wray, Michael T. Mellon, Shane Byrne, Alfred S. McEwen, Nathaniel E. Putzig, Donna Viola, Sarah Sutton, Erin Clark, John W. HoltFile:ESP 053867 2245hotejecta.jpg|Impact crater that may have formed in ice-rich ground, as seen by HiRISE under HiWish program Location is the Ismenius Lacus quadrangle.File:53867 2245hotejectamargin.jpg|Close view of impact crater that may have formed in ice-rich ground, as seen by HiRISE under HiWish program. Note that the ejecta seems lower than the surroundings. The hot ejecta may have caused some of the ice to go away; thus lowering the level of the ejecta.
Scalloped topography
Certain regions of Mars display scalloped-shaped depressions. The depressions are suspected to be the remains of a degrading ice-rich mantle deposit. Scallops are caused by ice sublimating from frozen soil. The landforms of scalloped topography can be formed by the subsurface loss of water ice by sublimation under current Martian climate conditions. A model predicts similar shapes when the ground has large amounts of pure ice, up to many tens of meters in depth.Dundas, C., S. Bryrne, A. McEwen. 2015. Modeling the development of martian sublimation thermokarst landforms. Icarus: 262, 154–169. This mantle material was probably deposited from the atmosphere as ice formed on dust when the climate was different due to changes in the tilt of the Mars pole (see "Ice ages", below).WEB,weblink HiRISE Dissected Mantled Terrain (PSP_002917_2175), Arizona University, December 19, 2010, The scallops are typically tens of meters deep and from a few hundred to a few thousand meters across. They can be almost circular or elongated. Some appear to have coalesced causing a large heavily pitted terrain to form. The process of forming the terrain may begin with sublimation from a crack. There are often polygonal cracks where scallops form, and the presence of scalloped topography seems to be an indication of frozen ground.JOURNAL, 10.1016/j.icarus.2009.06.005, Lefort, A., Russell, 2010, P.S., Thomas, N., Scalloped terrains in the Peneus and Amphitrites Paterae region of Mars as observed by HiRISE, Icarus, 205, 259–268, 2010Icar..205..259L, On November 22, 2016, NASA reported finding a large amount of underground ice in the Utopia Planitia region of Mars.WEB,weblink Huge Underground Ice Deposit on Mars Is Bigger Than New Mexico,, The volume of water detected has been estimated to be equivalent to the volume of water in Lake Superior.The volume of water ice in the region were based on measurements from the ground-penetrating radar instrument on Mars Reconnaissance Orbiter, called SHARAD. From the data obtained from SHARAD, “dielectric permittivity”, or the dielectric constant was determined. The dielectric constant value was consistent with a large concentration of water ice.Bramson, A, et al. 2015. Widespread excess ice in Arcadia Planitia, Mars. Geophysical Research Letters: 42, 6566–6574WEB,weblink Archived copy, November 29, 2016, yes,weblink November 30, 2016, Stuurman, C., et al. 2016. SHARAD detection and characterization of subsurface water ice deposits in Utopia Planitia, Mars. Geophysical Research Letters: 43, 9484_9491.These scalloped features are superficially similar to Swiss cheese features, found around the south polar cap. Swiss cheese features are thought to be due to cavities forming in a surface layer of solid carbon dioxide, rather than water ice—although the floors of these holes are probably H2O-rich.JOURNAL, A Sublimation Model for the Formation of the Martian Polar Swiss-cheese Features, Byrne, S., Ingersoll, A. P., 2002DPS....34.0301B, 34, 2002, 837, American Astronomical Society,
Ice patches
On July 28, 2005, the European Space Agency announced the existence of a crater partially filled with frozen water;PRESS RELEASE,weblink Water ice in crater at Martian north pole, July 27, 2005, ESA, some then interpreted the discovery as an "ice lake".NEWS,weblink Ice lake found on the Red Planet, July 29, 2005, BBC, Images of the crater, taken by the High Resolution Stereo Camera on board the European Space Agency's Mars Express orbiter, clearly show a broad sheet of ice in the bottom of an unnamed crater located on Vastitas Borealis, a broad plain that covers much of Mars' far northern latitudes, at approximately 70.5° North and 103° East. The crater is {{convert|35|km}} wide and about {{convert|2|km}} deep. The height difference between the crater floor and the surface of the water ice is about {{convert|200|m}}. ESA scientists have attributed most of this height difference to sand dunes beneath the water ice, which are partially visible. While scientists do not refer to the patch as a "lake", the water ice patch is remarkable for its size and for being present throughout the year. Deposits of water ice and layers of frost have been found in many different locations on the planet.As more and more of the surface of Mars has been imaged by the modern generation of orbiters, it has become gradually more apparent that there are probably many more patches of ice scattered across the Martian surface. Many of these putative patches of ice are concentrated in the Martian midlatitudes (≈30–60° N/S of the equator). For example, many scientists think that the widespread features in those latitude bands variously described as "latitude dependent mantle" or "pasted-on terrain" consist of dust- or debris-covered ice patches, which are slowly degrading. A cover of debris is required both to explain the dull surfaces seen in the images that do not reflect like ice, and also to allow the patches to exist for an extended period of time without subliming away completely. These patches have been suggested as possible water sources for some of the enigmatic channelized flow features like gullies also seen in those latitudes.Surface features consistent with existing pack ice have been discovered in the southern Elysium Planitia.BOOK, Cabrol, N., E., Grin, 2010, Lakes on Mars, Elsevier, New York, What appear to be plates, ranging in size from {{convert|30|m}} to {{convert|30|km}}, are found in channels leading to a large flooded area. The plates show signs of break up and rotation that clearly distinguish them from lava plates elsewhere on the surface of Mars. The source for the flood is thought to be the nearby geological fault Cerberus Fossae that spewed water as well as lava aged some 2 to 10 million years. It was suggested that the water exited the Cerberus Fossae then pooled and froze in the low, level plains and that such frozen lakes may still exist.JOURNAL, Murray, John B., etal, 2005, Evidence from the Mars Express High Resolution Stereo Camera for a frozen sea close to Mars' equator, Nature, 15772653, 434, 7031, 352–356, 10.1038/nature03379, Here we present High Resolution Stereo Camera images from the European Space Agency Mars Express spacecraft that indicate that such lakes may still exist., 2005Natur.434..352M, JOURNAL, Orosei, R., Cartacci, M., Cicchetti, A., Federico, C., Flamini, E., Frigeri, A., Holt, J. W., Marinangeli, L., Noschese, R., Pettinelli, E., Phillips, R. J., Picardi, G., Plaut, J. J., Safaeinili, A., Seu, R., Radar subsurface sounding over the putative frozen sea in Cerberus Palus, Mars,weblink 2007AGUFM.P14B..05O, 10.1109/ICGPR.2010.5550143, XXXIX, P14B–05, Lunar and Planetary Science, 2008, 978-1-4244-4604-9, BOOK, Mars: an introduction to its interior, surface and atmosphere, Barlow, Nadine G., Cambridge University Press, 978-0-521-85226-5, 2008-01-10,


File:Mars glacial-like lobe deposit.jpg|thumb|right|View of a 5-km-wide, glacial-like lobe deposit sloping up into a box canyon. The surface has morainemoraineMany large areas of Mars either appear to host glaciers, or carry evidence that they used to be present. Much of the areas in high latitudes, especially the Ismenius Lacus quadrangle, are suspected to still contain enormous amounts of water ice.BOOK, Strom, R.G., Steven K., Croft, Nadine G., Barlow, The Martian Impact Cratering Record, Mars, University of Arizona Press, 978-0-8165-1257-7, 1992, WEB,weblink ESA – Mars Express – Breathtaking views of Deuteronilus Mensae on Mars,, March 14, 2005, Recent evidence has led many planetary scientists to conclude that water ice still exists as glaciers across much of the Martian mid- and high latitudes, protected from sublimation by thin coverings of insulating rock and/or dust. An example of this are the glacier-like features called lobate debris aprons in an area called Deuteronilus Mensae, which display widespread evidence of ice lying beneath a few meters of rock debris. Glaciers are associated with fretted terrain, and many volcanoes. Researchers have described glacial deposits on Hecates Tholus,JOURNAL, Hauber, E., etal, 2005, Discovery of a flank caldera and very young glacial activity at Hecates Tholus, Mars, Nature, 434, 356–61, 15772654, 7031, 10.1038/nature03423, 2005Natur.434..356H, Arsia Mons,JOURNAL, Shean, David E., Head, James W., Fastook, James L., Marchant, David R., Recent glaciation at high elevations on Arsia Mons, Mars: Implications for the formation and evolution of large tropical mountain glaciers, E03004, 2007, E3, 112, 10.1029/2006JE002761, Journal of Geophysical Research,weblink 2007JGRE..112.3004S, Pavonis Mons,JOURNAL, Shean, D., etal, 2005, Origin and evolution of a cold-based mountain glacier on Mars: The Pavonis Mons fan-shaped deposit, Journal of Geophysical Research, 110, E5, E05001, 10.1029/2004JE002360, 2005JGRE..11005001S, and Olympus Mons.JOURNAL, Basilevsky, A., etal, 2006, Geological recent tectonic, volcanic and fluvial activity on the eastern flank of the Olympus Mons volcano, Mars, Geophysical Research Letters, 33, 13, L13201, 10.1029/2006GL026396, 2006GeoRL..3313201B,, Glaciers have also been reported in a number of larger Martian craters in the midlatitudes and above.File:Reull Vallis lineated deposits.jpg|thumb|left|Reull Vallis with lineated floor deposits. Location is Hellas quadrangleHellas quadrangleGlacier-like features on Mars are known variously as viscous flow features,JOURNAL, Milliken, R., etal, 2003, Viscous flow features on the surface of Mars: Observations from high-resolution Mars Orbiter Camera (MOC) images, Journal of Geophysical Research, 108, E6, 5057, 10.1029/2002je002005, 2003JGRE..108.5057M, Martian flow features, lobate debris aprons, or lineated valley fill, depending on the form of the feature, its location, the landforms it is associated with, and the author describing it. Many, but not all, small glaciers seem to be associated with gullies on the walls of craters and mantling material.JOURNAL, 10.1016/j.icarus.2004.05.026, Arfstrom, J., W., Hartmann, 2005, Martian flow features, moraine-like ridges, and gullies: Terrestrial analogs and interrelationships, Icarus, 174, 2, 321–35, 2005Icar..174..321A, The lineated deposits known as lineated valley fill are probably rock-covered glaciers that are found on the floors most channels within the fretted terrain found around Arabia Terra in the northern hemisphere. Their surfaces have ridged and grooved materials that deflect around obstacles. Lineated floor deposits may be related to lobate debris aprons, which have been proven to contain large amounts of ice by orbiting radar. For many years, researchers interpreted that features called 'lobate debris aprons' were glacial flows and it was thought that ice existed under a layer of insulating rocks.JOURNAL, Head, J. W., Neukum, G., Jaumann, R., Hiesinger, H., Hauber, E., Carr, M., Masson, P., Foing, B., Hoffmann, H., Kreslavsky, M., Werner, S., Milkovich, S., van Gasselt, S., HRSC Co-Investigator Team, Tropical to mid-latitude snow and ice accumulation, flow and glaciation on Mars, Nature, 434, 7031, 346–350, 2005, 15772652, 10.1038/nature03359, 2005Natur.434..346H, WEB, Staff, Brown University,weblink Mars' climate in flux: Mid-latitude glaciers, Marstoday, October 17, 2005, With new instrument readings, it has been confirmed that lobate debris aprons contain almost pure ice that is covered with a layer of rocks.File:Glacier close up with hirise.JPG|thumb|A ridge interpreted as the terminal moraine of an alpine glacier. Location is Ismenius Lacus quadrangleIsmenius Lacus quadrangleMoving ice carries rock material, then drops it as the ice disappears. This typically happens at the snout or edges of the glacier. On Earth, such features would be called moraines, but on Mars they are typically known as moraine-like ridges, concentric ridges, or arcuate ridges.JOURNAL, 10.1016/j.icarus.2005.05.011, Berman, D., etal, 2005, The role of arcuate ridges and gullies in the degradation of craters in the Newton Basin region of Mars, Icarus, 178, 2, 465–86, 2005Icar..178..465B, Because ice tends to sublime rather than melt on Mars, and because Mars's low temperatures tend to make glaciers "cold based" (frozen down to their beds, and unable to slide), the remains of these glaciers and the ridges they leave do not appear the exactly same as normal glaciers on Earth. In particular, Martian moraines tend to be deposited without being deflected by the underlying topography, which is thought to reflect the fact that the ice in Martian glaciers is normally frozen down and cannot slide. Ridges of debris on the surface of the glaciers indicate the direction of ice movement. The surface of some glaciers have rough textures due to sublimation of buried ice. The ice evaporates without melting and leaves behind an empty space. Overlying material then collapses into the void.WEB,weblink Fretted Terrain Valley Traverse,, January 16, 2012, Sometimes chunks of ice fall from the glacier and get buried in the land surface. When they melt, a more or less round hole remains. Many of these "kettle holes" have been identified on Mars.WEB,weblink Jumbled Flow Patterns, Arizona University, January 16, 2012, Despite strong evidence for glacial flow on Mars, there is little convincing evidence for landforms carved by glacial erosion, e.g., U-shaped valleys, crag and tail hills, arêtes, drumlins. Such features are abundant in glaciated regions on Earth, so their absence on Mars has proven puzzling. The lack of these landforms is thought to be related to the cold-based nature of the ice in most recent glaciers on Mars. Because the solar insolation reaching the planet, the temperature and density of the atmosphere, and the geothermal heat flux are all lower on Mars than they are on Earth, modelling suggests the temperature of the interface between a glacier and its bed stays below freezing and the ice is literally frozen down to the ground. This prevents it from sliding across the bed, which is thought to inhibit the ice's ability to erode the surface.

Development of Mars' water inventory

The variation in Mars's surface water content is strongly coupled to the evolution of its atmosphere and may have been marked by several key stages.File:Channels near Warrego in Thaumasia.JPG|thumb|250px|right|Dry channels near Warrego VallesWarrego Valles

Early Noachian era (4.6 Ga to 4.1 Ga)

{{more information|Noachian}}The early Noachian era was characterized by atmospheric loss to space from heavy meteoritic bombardment and hydrodynamic escape.JOURNAL, Jakosky, B. M., Phillips, R. J., 2001, Mars' volatile and climate history, Nature, 412, 6843, 237–244, 10.1038/35084184, 11449285, Ejection by meteorites may have removed ~60% of the early atmosphere.JOURNAL, Chaufray, J. Y., etal, 2007, Mars solar wind interaction: Formation of the Martian corona and atmospheric loss to space, Journal of Geophysical Research, 112, E9, E09009, 10.1029/2007JE002915, 2007JGRE..112.9009C, Significant quantities of phyllosilicates may have formed during this period requiring a sufficiently dense atmosphere to sustain surface water, as the spectrally dominant phyllosilicate group, smectite, suggests moderate water-to-rock ratios.JOURNAL, Chevrier, V., etal, 2007, Early geochemical environment of Mars as determined from thermodynamics of phyllosilicates, Nature, 448, 7149, 60–63, 10.1038/nature05961, 17611538, 2007Natur.448...60C, However, the pH-pCO2 between smectite and carbonate show that the precipitation of smectite would constrain pCO2 to a value not more than {{convert|1e-2|atm|abbr=on}}. As a result, the dominant component of a dense atmosphere on early Mars becomes uncertain, if the clays formed in contact with the Martian atmosphere,JOURNAL, Catling, D. C., 2007, Mars: Ancient fingerprints in the clay, Nature, 448, 7149, 31–32, 10.1038/448031a, 17611529, 2007Natur.448...31C, particularly given the lack of evidence for carbonate deposits. An additional complication is that the ~25% lower brightness of the young Sun would have required an ancient atmosphere with a significant greenhouse effect to raise surface temperatures to sustain liquid water. Higher CO2 content alone would have been insufficient, as CO2 precipitates at partial pressures exceeding {{convert|1.5|atm|hPa|abbr=on}}, reducing its effectiveness as a greenhouse gas.

Middle to late Noachean era (4.1 Ga to 3.8 Ga)

During the middle to late Noachean era, Mars underwent potential formation of a secondary atmosphere by outgassing dominated by the Tharsis volcanoes, including significant quantities of H2O, CO2, and SO2. Martian valley networks date to this period, indicating globally widespread and temporally sustained surface water as opposed to catastrophic floods. The end of this period coincides with the termination of the internal magnetic field and a spike in meteoritic bombardment. The cessation of the internal magnetic field and subsequent weakening of any local magnetic fields allowed unimpeded atmospheric stripping by the solar wind. For example, when compared with their terrestrial counterparts, 38Ar/36Ar, 15N/14N, and 13C/12C ratios of the Martian atmosphere are consistent with ~60% loss of Ar, N2, and CO2 by solar wind stripping of an upper atmosphere enriched in the lighter isotopes via Rayleigh fractionation. Supplementing the solar wind activity, impacts would have ejected atmospheric components in bulk without isotopic fractionation. Nevertheless, cometary impacts in particular may have contributed volatiles to the planet.

Hesperian to Amazonian era (present) (~3.8 Ga to present)

{{more information|Hesperian|Amazonian (Mars)}}Atmospheric enhancement by sporadic outgassing events were countered by solar wind stripping of the atmosphere, albeit less intensely than by the young Sun. Catastrophic floods date to this period, favoring sudden subterranean release of volatiles, as opposed to sustained surface flows. While the earlier portion of this era may have been marked by aqueous acidic environments and Tharsis-centric groundwater dischargeJOURNAL, Andrews-Hanna, J. C., etal, 2007, Meridiani Planum and the global hydrology of Mars, Nature, 446, 7132, 163–6, 10.1038/nature05594, 17344848, 2007Natur.446..163A, dating to the late Noachian, much of the surface alteration processes during the latter portion is marked by oxidative processes including the formation of Fe3+ oxides that impart a reddish hue to the Martian surface. Such oxidation of primary mineral phases can be achieved by low-pH (and possibly high temperature) processes related to the formation of palagonitic tephra,JOURNAL, Morris, R. V., etal, 2001, Phyllosilicate-poor palagonitic dust from Mauna Kea Volcano (Hawaii): A mineralogical analogue for magnetic Martian dust?, Journal of Geophysical Research, 106, E3, 5057–5083, 10.1029/2000JE001328, 2001JGR...106.5057M, by the action of H2O2 that forms photochemically in the Martian atmosphere,JOURNAL, Chevrier, V., etal, 2006, Iron weathering products in a CO2+(H2O or H2O2) atmosphere: Implications for weathering processes on the surface of Mars, Geochimica et Cosmochimica Acta, 70, 16, 4295–4317, 10.1016/j.gca.2006.06.1368, 2006GeCoA..70.4295C, and by the action of water, none of which require free O2. The action of H2O2 may have dominated temporally given the drastic reduction in aqueous and igneous activity in this recent era, making the observed Fe3+ oxides volumetrically small, though pervasive and spectrally dominant.JOURNAL, Bibring, J-P., etal, 2006, Global mineralogical and aqueous mars history derived from OMEGA/Mars Express data, Science, 312, 5772, 400–4, 10.1126/science.1122659, 16627738, 2006Sci...312..400B, Nevertheless, aquifers may have driven sustained, but highly localized surface water in recent geologic history, as evident in the geomorphology of craters such as Mojave.JOURNAL, McEwen, A. S., etal, 2007, A Closer Look at Water-Related Geologic Activity on Mars, Science, 317, 5845, 1706–1709, 10.1126/science.1143987, 17885125, 2007Sci...317.1706M, Furthermore, the Lafayette Martian meteorite shows evidence of aqueous alteration as recently as 650 Ma.

Ice ages

(File:Conical mound in trough on Mars' north pole.jpg|thumb|North polar layered deposits of ice and dust)Mars has experienced about 40 large scale changes in the amount and distribution of ice on its surface over the past five million years,JOURNAL, Schorghofer, Norbert, 2007, Dynamics of ice ages on Mars,weblink Nature, 449, 7159, 192–194, 2007Natur.449..192S, 10.1038/nature06082, 17851518, JOURNAL, Shean, David E., Origin and evolution of a cold-based tropical mountain glacier on Mars: The Pavonis Mons fan-shaped deposit, Journal of Geophysical Research, 110, 2005, 10.1029/2004JE002360, 2005JGRE..11005001S, with the most recent happening about 2.1 to 0.4 Myr ago, during the Late Amazonian glaciation at the dichotomy boundary.JOURNAL, Dickson, James L., Head, James W., Marchant, David R., 2008, Late Amazonian glaciation at the dichotomy boundary on Mars: Evidence for glacial thickness maxima and multiple glacial phases, Geology (journal), Geology, 36, 5, 411–4, 10.1130/G24382A.1, 2008Geo....36..411D, JOURNAL, Head, J. W., III, Mustard, J. F., Kreslavsky, M. A., Milliken, R. E., Marchant, D. R., 2003, Recent ice ages on Mars, Nature, 426, 6968, 797–802, 10.1038/nature02114, 14685228, 2003Natur.426..797H, These changes are known as ice ages.JOURNAL, An ice age recorded in the polar deposits of Mars, Science, May 27, 2016, Smith, Isaac B., Putzig, Nathaniel E., Holt, John W., Phillips, Roger J., 352, 6289, 1075–1078, 10.1126/science.aad6968, 27230372, 2016Sci...352.1075S, Ice ages on Mars are very different from the ones that the Earth experiences. Ice ages are driven by changes in Mars's orbit and tilt —also known as obliquity. Orbital calculations show that Mars wobbles on its axis far more than Earth does. The Earth is stabilized by its proportionally large moon, so it only wobbles a few degrees. Mars may change its tilt by many tens of degrees.JOURNAL, Levrard, B., Forget, F., Montmessian, F., Laskar, J., 2004, Recent ice-rich deposits formed at high latitudes on Mars by sublimation of unstable equatorial ice during low obliquity, Nature, 431, 7012, 1072–1075, 10.1038/nature03055, 15510141, 2004Natur.431.1072L, When this obliquity is high, its poles get much more direct sunlight and heat; this causes the ice caps to warm and become smaller as ice sublimes. Adding to the variability of the climate, the eccentricity of the orbit of Mars changes twice as much as Earth's eccentricity. As the poles sublime, the ice is redeposited closer to the equator, which receive somewhat less solar insolation at these high obliquities. Computer simulations have shown that a 45° tilt of the Martian axis would result in ice accumulation in areas that display glacial landforms.JOURNAL, Forget, F., etal, 2006, Formation of Glaciers on Mars by Atmospheric Precipitation at High Obliquity, Science, 311, 368–71, 16424337, 5759, 10.1126/science.1120335, 2006Sci...311..368F, The moisture from the ice caps travels to lower latitudes in the form of deposits of frost or snow mixed with dust. The atmosphere of Mars contains a great deal of fine dust particles, the water vapor condenses on these particles that then fall down to the ground due to the additional weight of the water coating. When ice at the top of the mantling layer returns to the atmosphere, it leaves behind dust that serves to insulate the remaining ice. The total volume of water removed is a few percent of the ice caps, or enough to cover the entire surface of the planet under one meter of water. Much of this moisture from the ice caps results in a thick smooth mantle with a mixture of ice and dust.JOURNAL, Mustard, J., etal, 2001, Evidence for recent climate change on Mars from the identification of youthful near-surface ground ice, Nature, 412, 411–4, 11473309, 6845, 10.1038/35086515, 2001Natur.412..411M, JOURNAL, Kreslavsky, M., J., Head, 2002, Mars: Nature and evolution of young latitude-dependent water-ice-rich mantle, 15, Geophysical Research Letters, 29,weblink 10.1029/2002GL015392, 2002GeoRL..29.1719K, 14–1–14–4, This ice-rich mantle, that can be 100 meters thick at mid-latitudes,WEB, Beatty, Kelly, Water Ice Found Exposed in Martian Cliffs - Sky & Telescope,weblink Sky & Telescope, 3 October 2018, 23 January 2018, smoothes the land at lower latitudes, but in places it displays a bumpy texture or patterns that give away the presence of water ice underneath.

Evidence for recent flows

{{See also|Gully (Mars)}}File:Warm Season Flows on Slope in Newton Crater (animated).gif|thumb|left|Warm-season flows on slope in Newton Crater ]](File:Branched gullies.jpg|thumb|Branched gullies)(File:Deep Gullies.jpg|thumb|Group of deep gullies)Pure liquid water cannot exist in a stable form on the surface of Mars with its present low atmospheric pressure and low temperature, except at the lowest elevations for a few hours. So, a geological mystery commenced in 2006 when observations from NASA's Mars Reconnaissance Orbiter revealed gully deposits that were not there ten years prior, possibly caused by flowing liquid brine during the warmest months on Mars.JOURNAL, Present-Day Impact Cratering Rate and Contemporary Gully Activity on Mars, Science, December 8, 2006, Michael C., Malin, Kenneth S., Edgett, Liliya V., Posiolova, Shawn M., McColley, Eldar Z. Noe, Dobrea, 314, 5805, 1573–1577, 10.1126/science.1135156, 17158321, 2006Sci...314.1573M, JOURNAL, 18725636, 2008, Head, JW, Marchant, DR, Kreslavsky, MA, Formation of gullies on Mars: Link to recent climate history and insolation microenvironments implicate surface water flow origin, 105, 36, 13258–63, 10.1073/pnas.0803760105, 2734344, Proceedings of the National Academy of Sciences of the United States of America, PNAS, 2008PNAS..10513258H, The images were of two craters called Terra Sirenum and Centauri Montes that appear to show the presence of flows (wet or dry) on Mars at some point between 1999 and 2001.NEWS,weblink Water has been flowing on Mars within past five years, Nasa says, The Times, UK, Mark, Henderson, December 7, 2006, JOURNAL, Malin, Michael C., Edgett, Kenneth S., 2000, Evidence for Recent Groundwater Seepage and Surface Runoff on Mars, Science, 288, 5475, 2330–2335, 10.1126/science.288.5475.2330, 10875910, 2000Sci...288.2330M, There is disagreement in the scientific community as to whether or not gullies are formed by liquid water. It is also possible that the flows that carve gullies are dry grains,JOURNAL, 10.1016/j.icarus.2009.09.009, Kolb, K., Pelletier, 2010, Jon D., McEwen, Alfred S., Modeling the formation of bright slope deposits associated with gullies in Hale Crater, Mars: Implications for recent liquid water, Icarus, 205, 1, 113–137, 2010Icar..205..113K, or perhaps lubricated by carbon dioxide. Some studies attest that gullies forming in the southern highlands could not be formed by water due to improper conditions. The low pressure, non-geothermal, colder regions would not give way to liquid water at any point in the year but would be ideal for solid carbon dioxide. The carbon dioxide melting in the warmer summer would yield liquid carbon dioxide which would then form the gullies.JOURNAL, Hoffman, Nick, Active polar gullies on Mars and the role of carbon dioxide, Astrobiology, 2, 3, 2002, 313–323, 10.1089/153110702762027899, 12530241, 2002AsBio...2..313H, JOURNAL, Musselwhite, Donald S., Timothy D., Swindle, Jonathan I., Lunine, Liquid CO2 breakout and the formation of recent small gullies on Mars, Geophysical Research Letters, 28, 7, 2001, 1283–1285, 10.1029/2000gl012496, 2001GeoRL..28.1283M, Even if gullies are carved by flowing water at the surface, the exact source of the water and the mechanisms behind its motion are not understood.JOURNAL, McEwen, Alfred. S., Ojha, Lujendra, Dundas, Colin M., June 17, 2011, Seasonal Flows on Warm Martian Slopes, Science, 333, 6043, 740–743, American Association for the Advancement of Science, 10.1126/science.1204816, 0036-8075, 2011Sci...333..740M, 21817049, The dry gullies are deep grooves etched into the slopes that are there year-round. There are many other features on Mars, and some of them change seasonally.In August 2011, NASA announced the discovery by undergraduate student Lujendra OjhaWEB,weblink Nepali Scientist Lujendra Ojha spots possible water on Mars, Nepali Blogger, August 6, 2011, yes,weblink" title="">weblink June 4, 2013, of current seasonal changes on steep slopes below rocky outcrops near crater rims in the Southern hemisphere. These dark streaks, now called recurrent slope lineae (RSL), were seen to grow downslope during the warmest part of the Martian Summer, then to gradually fade through the rest of the year, recurring cyclically between years. The researchers suggested these marks were consistent with salty water (brines) flowing downslope and then evaporating, possibly leaving some sort of residue.WEB,weblink NASA Spacecraft Data Suggest Water Flowing on Mars, NASA, August 4, 2011, JOURNAL, McEwen, Alfred, Lujendra, Ojha, Dundas, Colin, Mattson, Sarah, Bryne, S, Wray, J, Cull, Selby, Murchie, Scott, Thomas, Nicholas, Gulick, Virginia, Seasonal Flows On Warm Martian Slopes., Science, August 5, 2011, 333, 6043, 743, 10.1126/science.1204816, 21817049,weblink September 29, 2015, mdy-all, 2011Sci...333..740M, The CRISM spectroscopic instrument has since made direct observations of hydrous salts appearing at the same time that these recurrent slope lineae form, confirming in 2015 that these lineae are produced by the flow of liquid brines through shallow soils. The lineae contain hydrated chlorate and perchlorate salts ({{chem|Cl|O|4}}−), which contain liquid water molecules.WEB, NASA Finds 'Definitive' Liquid Water on Mars,weblink National Geographic News, September 30, 2015, Nadia, Drake, National Geographic September, 28, September 28, 2015, The lineae flow downhill in Martian summer, when the temperature is above {{convert|-23|C|F K}}.WEB, Water Flows on Mars Today, NASA Announces,weblink September 30, 2015, Clara, Moskowitz, However, the source of the water remains unknown.WEB,weblink NASA News Conference: Evidence of Liquid Water on Today's Mars, September 28, 2015, NASA, WEB, NASA Confirms Evidence That Liquid Water Flows on Today's Mars,weblink September 30, 2015, September 28, 2015, However, neutron spectrometer data by the Mars Odyssey orbiter obtained over one decade, was published in December 2017, and shows no evidence of water (hydrogenated regolith) at the active sites, so its authors also support the hypotheses of either short-lived atmospheric water vapour deliquesence, or dry granular flows. They conclude that liquid water on today's Mars may be limited to traces of dissolved moisture from the atmosphere and thin films, which are challenging environments for life as we know it.Recurring Martian Streaks: Flowing Sand, Not Water?. JPL NASA News. November 20, 2017.

Habitability assessments

File:Sagan Viking.jpg|thumb|Carl SaganCarl SaganFile:Mars rover being tested near the Paranal Observatory.jpg|thumb|ExoMars rover prototype being tested in the Atacama DesertAtacama DesertSince the Viking landers that searched for current microbial life in 1976, NASA has pursued a "follow the water" strategy on Mars. However, liquid water is a necessary but not sufficient condition for life as we know it because habitability is a function of a multitude of environmental parameters.Astrobiology Strategy 2015 (PDF) NASA. Chemical, physical, geological, and geographic attributes shape the environments on Mars. Isolated measurements of these factors may be insufficient to deem an environment habitable, but the sum of measurements can help predict locations with greater or lesser habitability potential.JOURNAL, 2013LPI....44.2185C, Habitability Assessment at Gale Crater: Implications from Initial Results, Conrad, P. G., Archer, D., Coll, P., De La Torre, M., Edgett, K., Eigenbrode, J. L., Fisk, M., Freissenet, C., Franz, H., Glavin, D. P., Gómez, F., Haberle, R., Hamilton, V., Jones, J. H., Kah, L. C., Leshin, L. A., Mahaffy, P. M., McAdam, A., McKay, C. P., Navarro-González, R., Steele, A., Stern, J., Sumner, D., Treiman, A. H., Wong, M. H., Wray, J., Yingst, R. A., MSL Science Team, 9, 1719, 1719, 2013, 2185, 44th Lunar and Planetary Science Conference, Habitable environments need not be inhabited, and for purposes of planetary protection, scientists are trying to identify potential habitats where stowaway bacteria from Earth on spacecraft could contaminate Mars.BOOK, Committee on an Astrobiology Strategy for the Exploration of Mars, National Research Council, 2007, Planetary Protection for Mars Missions,weblink 95–98, An Astrobiology Strategy for the Exploration of Mars, The National Academies Press, 978-0-309-10851-5, If life exists —or existed— on Mars, evidence or biosignatures could be found in the subsurface, away from present-day harsh surface conditions such as perchlorates,NEWS, Daley, Jason, Mars Surface May Be Too Toxic for Microbial Life - The combination of UV radiation and perchlorates common on Mars could be deadly for bacteria,weblink 6 July 2017, Smithsonian (magazine), Smithsonian, 8 July 2017, JOURNAL, Wadsworth, Jennifer, Cockell, Charles S., Perchlorates on Mars enhance the bacteriocidal effects of UV light, 6 July 2017, Scientific Reports, 7, 4662, 4662, 10.1038/s41598-017-04910-3, 2017NatSR...7.4662W, 28684729, 5500590, ionizing radiation, desiccation and freezing.WEB,weblink NASA Astrobiology Strategy, 2015, NASA., September 5, 2018,weblink December 22, 2016, yes, Habitable locations could occur kilometers below the surface in a hypothetical hydrosphere, or it could occur near the sub-surface in contact with permafrost.The Curiosity rover is assessing Mars' past and present habitability potential. The European-Russian ExoMars programme is an astrobiology project dedicated to the search for and identification of biosignatures on Mars. It includes the ExoMars Trace Gas Orbiter that started mapping the atmospheric methane in April 2018, and the 2020 ExoMars rover that will drill and analyze subsurface samples 2 meters deep. NASA's Mars 2020 rover will cache dozens of drilled core samples for their potential transport to Earth laboratories in the late 2020s or 2030s.

Findings by probes

Mariner 9

File:Scamander Vallis from Mars Global Surveyor.jpg|thumb|Meander in Scamander Vallis, as seen by Mars Global SurveyorMars Global SurveyorThe images acquired by the Mariner 9 Mars orbiter, launched in 1971, revealed the first direct evidence of past water in the form of dry river beds, canyons (including the Valles Marineris, a system of canyons over about {{convert|4020|km|mi|-1}} long), evidence of water erosion and deposition, weather fronts, fogs, and more.WEB,weblink Mars Exploration: Missions,, December 19, 2010, The findings from the Mariner 9 missions underpinned the later Viking program. The enormous Valles Marineris canyon system is named after Mariner 9 in honor of its achievements.

Viking program

File:Streamlined Islands in Maja Valles.jpg|thumb|left|Streamlined islands in Maja VallesMaja VallesBy discovering many geological forms that are typically formed from large amounts of water, the two Viking orbiters and the two landers caused a revolution in our knowledge about water on Mars. Huge outflow channels were found in many areas. They showed that floods of water broke through dams, carved deep valleys, eroded grooves into bedrock, and traveled thousands of kilometers.WEB,weblink Viking Orbiter Views of Mars,, December 19, 2010, Large areas in the southern hemisphere contained branched valley networks, suggesting that rain once fell.WEB,weblink ch5, NASA History, NASA, December 19, 2010, Many craters look as if the impactor fell into mud. When they were formed, ice in the soil may have melted, turned the ground into mud, then the mud flowed across the surface.JOURNAL, Raeburn, P., 1998, Uncovering the Secrets of the Red Planet Mars, National Geographic, Washington D.C., BOOK, Moore, P., etal, 1990, The Atlas of the Solar System, Mitchell Beazley Publishers, New York, WEB,weblink Craters, NASA, December 19, 2010, Regions, called "Chaotic Terrain," seemed to have quickly lost great volumes of water that caused large channels to form downstream. Estimates for some channel flows run to ten thousand times the flow of the Mississippi River.BOOK, Morton, O., 2002, Mapping Mars, Picador, NY, Underground volcanism may have melted frozen ice; the water then flowed away and the ground collapsed to leave chaotic terrain. Also, general chemical analysis by the two Viking landers suggested the surface has been either exposed to or submerged in water in the past.JOURNAL, 10.1029/RG027i001p00039, Arvidson, R, Gooding, James L., Moore, Henry J., 1989, The Martian surface as Imaged, Sampled, and Analyzed by the Viking Landers, Reviews of Geophysics, 27, 1, 39–60, 1989RvGeo..27...39A, JOURNAL, 10.1126/science.194.4271.1283, Clark, B., Baird, AK, Rose Jr., HJ, Toulmin P, 3rd, Keil, K, Castro, AJ, Kelliher, WC, Rowe, CD, Evans, PH, 1976, Inorganic Analysis of Martian Samples at the Viking Landing Sites, Science, 194, 4271, 1283–1288, 17797084, 1976Sci...194.1283C,

Mars Global Surveyor

File:Hematite region Sinus Meridiani sur Mars.jpg|thumb|Map showing the distribution of hematitehematiteThe Mars Global Surveyor's Thermal Emission Spectrometer (TES) is an instrument able to determine the mineral composition on the surface of Mars. Mineral composition gives information on the presence or absence of water in ancient times. TES identified a large ({{convert|30000|km²}}) area in the Nili Fossae formation that contains the mineral olivine.JOURNAL, Hoefen, T.M., etal, 2003, Discovery of Olivine in the Nili Fossae Region of Mars, Science, 302, 5645, 627–630, 10.1126/science.1089647, 14576430, 2003Sci...302..627H,weblink It is thought that the ancient asteroid impact that created the Isidis basin resulted in faults that exposed the olivine. The discovery of olivine is strong evidence that parts of Mars have been extremely dry for a long time. Olivine was also discovered in many other small outcrops within 60 degrees north and south of the equator.JOURNAL, 10.1126/science.1089647, Hoefen, T., Clark, RN, Bandfield, JL, Smith, MD, Pearl, JC, Christensen, PR, 2003, Discovery of Olivine in the Nili Fossae Region of Mars, Science, 302, 5645, 627–630, 14576430, 2003Sci...302..627H,weblink The probe has imaged several channels that suggest past sustained liquid flows, two of them are found in Nanedi Valles and in Nirgal Vallis.JOURNAL, Malin, Michael C., Edgett, Kenneth S., Mars Global Surveyor Mars Orbiter Camera: Interplanetary cruise through primary mission, 23429–23570, Journal of Geophysical Research, 2001, 10.1029/2000JE001455, 106, 2001JGR...10623429M, E10, File:Nanedi channel.JPG|thumb|Inner channel (near top of the image) on floor of Nanedi Valles that suggests that water flowed for a fairly long period. Image from Lunae Palus quadrangleLunae Palus quadrangle

Mars Pathfinder

The Pathfinder lander recorded the variation of diurnal temperature cycle. It was coldest just before sunrise, about {{convert|−78|C|F K}}, and warmest just after Mars noon, about {{convert|−8|C|F K}}. At this location, the highest temperature never reached the freezing point of water ({{convert|0|C|F K}}), too cold for pure liquid water to exist on the surface.The atmospheric pressure measured by the Pathfinder on Mars is very low —about 0.6% of Earth's, and it would not permit pure liquid water to exist on the surface.WEB,weblink Atmospheric and Meteorological Properties, NASA, Other observations were consistent with water being present in the past. Some of the rocks at the Mars Pathfinder site leaned against each other in a manner geologists term imbricated. It is suspected that strong flood waters in the past pushed the rocks around until they faced away from the flow. Some pebbles were rounded, perhaps from being tumbled in a stream. Parts of the ground are crusty, maybe due to cementing by a fluid containing minerals. There was evidence of clouds and maybe fog.JOURNAL, 10.1126/science.278.5344.1743, Golombek, M. P., Cook, R. A., Economou, T., Folkner, W. M., Haldemann, A. F. C., Kallemeyn, P. H., Knudsen, J. M., Manning, R. M., Moore, H. J., Parker, T. J., Rieder, R., Schofield, J. T., Smith, P. H., Vaughan, R. M., Overview of the Mars Pathfinder Mission and Assessment of Landing Site Predictions, Science, 278, 5344, 1743–1748, 9388167, 1997Sci...278.1743G, 1997,

Mars Odyssey

File:Semeykin Crater Drainage.JPG|thumb|left|Complex drainage system in Semeykin Crater. Location is Ismenius Lacus quadrangleIsmenius Lacus quadrangleThe 2001 Mars Odyssey found much evidence for water on Mars in the form of images, and with its neutron spectrometer, it proved that much of the ground is loaded with water ice. Mars has enough ice just beneath the surface to fill Lake Michigan twice.WEB,weblink Mars Odyssey: Newsroom,, May 28, 2002, In both hemispheres, from 55° latitude to the poles, Mars has a high density of ice just under the surface; one kilogram of soil contains about {{convert|500|g}} of water ice. But close to the equator, there is only 2% to 10% of water in the soil.JOURNAL, 2004, Feldman, W.C., etal, Global Distribution of Near-Surface Hydrogen on Mars, Journal of Geophysical Research, 109, 10.1029/2003JE002160, 2004JGRE..10909006F, Scientists think that much of this water is also locked up in the chemical structure of minerals, such as clay and sulfates.JOURNAL, 10.1006/icar.1993.1141, Murche, S., Mustard, John, 1993, Spatial Variations in the Spectral Properties of Bright Regions on Mars, Icarus, 105, 454–468, 1993Icar..105..454M, 2, Bishop, Janice, Head, James, Pieters, Carle, Erard, Stephane, WEB,weblink Home Page for Bell (1996) Geochemical Society paper,, December 19, 2010, Although the upper surface contains a few percent of chemically-bound water, ice lies just a few meters deeper, as it has been shown in Arabia Terra, Amazonis quadrangle, and Elysium quadrangle that contain large amounts of water ice.JOURNAL, 10.1126/science.1073541, Feldman, W. C., Boynton, W. V., Tokar, R. L., Prettyman, T. H., Gasnault, O., Squyres, S. W., Elphic, R. C., Lawrence, D. J., Lawson, S. L., Maurice, S., McKinney, G. W., Moore, K. R., Reedy, R. C., Global Distribution of Neutrons from Mars: Results from Mars Odyssey, Science, 297, 5578, 75–78, 12040088, 2002Sci...297...75F, 2002, The orbiter also discovered vast deposits of bulk water ice near the surface of equatorial regions. Evidence for equatorial hydration is both morphological and compositional and is seen at both the Medusae Fossae formation and the Tharsis Montes. Analysis of the data suggests that the southern hemisphere may have a layered structure, suggestive of stratified deposits beneath a now extinct large water mass.JOURNAL, 10.1126/science.1073616, Mitrofanov, I., Anfimov, D., Kozyrev, A., Litvak, M., Sanin, A., Tret'yakov, V., Krylov, A., Shvetsov, V., Boynton, W., Shinohara, C., Hamara, D., Saunders, R. S., Maps of Subsurface Hydrogen from the High Energy Neutron Detector, Mars Odyssey, Science, 297, 5578, 78–81, 12040089, 2002Sci...297...78M, 2002, File:Blocks in Aram.JPG|thumb|Blocks in Aram showing a possible ancient source of water. Location is Oxia Palus quadrangleOxia Palus quadrangleThe instruments aboard the Mars Odyssey are able to study the top meter of soil. In 2002, available data were used to calculate that if all soil surfaces were covered by an even layer of water, this would correspond to a global layer of water (GLW) {{convert|0.5-1.5|km}}.JOURNAL, 10.1126/science.1073722, Boynton, W. V., Feldman, W. C., Squyres, S. W., Prettyman, T. H., Brückner, J., Evans, L. G., Reedy, R. C., Starr, R., Arnold, J. R., Drake, D. M., Englert, P. A. J., Metzger, A. E., Mitrofanov, Igor, Trombka, J. I., d'Uston, C., Wänke, H., Gasnault, O., Hamara, D. K., Janes, D. M., Marcialis, R. L., Maurice, S., Mikheeva, I., Taylor, G. J., Tokar, R., Shinohara, C., Distribution of Hydrogen in the Near Surface of Mars: Evidence for Subsurface Ice Deposits, Science, 297, 5578, 81–85, 12040090, 2002Sci...297...81B, 2002, Thousands of images returned from Odyssey orbiter also support the idea that Mars once had great amounts of water flowing across its surface. Some images show patterns of branching valleys; others show layers that may have been formed under lakes; even river and lake deltas have been identified.JOURNAL, Irwin, Rossman P., Howard, Alan D., Craddock, Robert A., Moore, Jeffrey M., An intense terminal epoch of widespread fluvial activity on early Mars: 2. Increased runoff and paleolake development, Journal of Geophysical Research, 110, E12, E12S15, 2005, 10.1029/2005JE002460, 2005JGRE..11012S15I, WEB,weblink Dao Vallis, August 7, 2002, Mars Odyssey Mission, THEMIS, December 19, 2010, For many years researchers suspected that glaciers exist under a layer of insulating rocks. Lineated valley fill is one example of these rock-covered glaciers. They are found on the floors of some channels. Their surfaces have ridged and grooved materials that deflect around obstacles. Lineated floor deposits may be related to lobate debris aprons, which have been shown by orbiting radar to contain large amounts of ice.


File:Phoenix Sol 0 horizon.jpg|thumb|PermafrostPermafrostThe Phoenix lander also confirmed the existence of large amounts of water ice in the northern region of Mars.JOURNAL, Smith, P. H., Tamppari, L., Arvidson, R. E., Bass, D., Blaney, D., Boynton, W., Carswell, A., Catling, D., Clark, B., Duck, T., DeJong, E., Fisher, D., Goetz, W., Gunnlaugsson, P., Hecht, M., Hipkin, V., Hoffman, J., Hviid, S., Keller, H., Kounaves, S., Lange, C. F., Lemmon, M., Madsen, M., Malin, M., Markiewicz, W., Marshall, J., McKay, C., Mellon, M., Michelangeli, D., Ming, D., Morris, R., Renno, N., Pike, W. T., Staufer, U., Stoker, C., Taylor, P., Whiteway, J., Young, S., Zent, A., Introduction to special section on the phoenix mission: Landing site characterization experiments, mission overviews, and expected science, Journal of Geophysical Research, 113, E12, E00A18, 10.1029/2008JE003083, 2008JGRE..113.0A18S, 2008, 29, 2027.42/94752, WEB,weblink NASA Data Shed New Light About Water and Volcanoes on Mars, NASA, September 9, 2010, March 21, 2014, This finding was predicted by previous orbital data and theory,JOURNAL, Mellon, M., Jakosky, B., 1993, Geographic variations in the thermal and diffusive stability of ground ice on Mars, Journal of Geophysical Research, 98, E2, 3345–3364, 10.1029/92JE02355, 1993JGR....98.3345M, and was measured from orbit by the Mars Odyssey instruments. On June 19, 2008, NASA announced that dice-sized clumps of bright material in the "Dodo-Goldilocks" trench, dug by the robotic arm, had vaporized over the course of four days, strongly indicating that the bright clumps were composed of water ice that sublimes following exposure. Even though CO2 (dry ice) also sublimes under the conditions present, it would do so at a rate much faster than observed.WEB,weblink Confirmation of Water on Mars,, June 20, 2008, On July 31, 2008, NASA announced that Phoenix further confirmed the presence of water ice at its landing site. During the initial heating cycle of a sample, the mass spectrometer detected water vapor when the sample temperature reached {{convert|0|C|F K}}.NEWS, Johnson, John, There's water on Mars, NASA confirms, Los Angeles Times, August 1, 2008,weblink Liquid water cannot exist on the surface of Mars with its present low atmospheric pressure and temperature, except at the lowest elevations for short periods.JOURNAL, Geophysical Research Letters, 33, 11, L11201, June 3, 2006, Kostama, V.-P., Kreslavsky, M. A., Head, J. W., Recent high-latitude icy mantle in the northern plains of Mars: Characteristics and ages of emplacement,weblink 10.1029/2006GL025946, 2006GeoRL..3311201K,, JOURNAL, Journal of Geophysical Research, May 7, 2005, Heldmann, Jennifer L., etal, Formation of Martian gullies by the action of liquid water flowing under current Martian environmental conditions,weblink 110, Eo5004, 10.1029/2004JE002261, 2005JGRE..11005004H, 2060/20050169988, 'conditions such as now occur on Mars, outside of the temperature-pressure stability regime of liquid water' … 'Liquid water is typically stable at the lowest elevations and at low latitudes on the planet, because the atmospheric pressure is greater than the vapor pressure of water and surface temperatures in equatorial regions can reach {{convert|220|K|C F}} for parts of the day.WEB,weblink The Dirt on Mars Lander Soil Findings,, December 19, 2010, Perchlorate (ClO4), a strong oxidizer, was confirmed to be in the soil. The chemical, when mixed with water, can lower the water freezing point in a manner similar to how salt is applied to roads to melt ice.(File:PIA10741 Possible Ice Below Phoenix.jpg|thumb|left|View underneath Phoenix lander showing water ice exposed by the landing retrorockets)When Phoenix landed, the retrorockets splashed soil and melted ice onto the vehicle.JOURNAL, Martínez, G. M., Renno, N. O., yes, 2013, Water and brines on Mars: current evidence and implications for MSL, Space Science Reviews, 175, 1–4, 29–51, 10.1007/s11214-012-9956-3, 2013SSRv..175...29M, Photographs showed the landing had left blobs of material stuck to the landing struts. The blobs expanded at a rate consistent with deliquescence, darkened before disappearing (consistent with liquefaction followed by dripping), and appeared to merge. These observations, combined with thermodynamic evidence, indicated that the blobs were likely liquid brine droplets.JOURNAL, 10.1029/2009JE003362, Possible physical and thermodynamical evidence for liquid water at the Phoenix landing site, 2009, Rennó, Nilton O., Bos, Brent J., Catling, David, Clark, Benton C., Drube, Line, Fisher, David, Goetz, Walter, Hviid, Stubbe F., Keller, Horst Uwe, Kok, Jasper F., Kounaves, Samuel P., Leer, Kristoffer, Lemmon, Mark, Madsen, Morten Bo, Markiewicz, Wojciech J., Marshall, John, McKay, Christopher, Mehta, Manish, Smith, Miles, Zorzano, M. P., Smith, Peter H., Stoker, Carol, Young, Suzanne M. M., Journal of Geophysical Research, 114, E1, E00E03, 2009JGRE..114.0E03R, 2027.42/95444, Other researchers suggested the blobs could be "clumps of frost."WEB, Chang, Kenneth,weblink Blobs in Photos of Mars Lander Stir a Debate: Are They Water?, New York Times (online), March 16, 2009, WEB,weblink Liquid Saltwater Is Likely Present On Mars, New Analysis Shows, ScienceDaily, March 20, 2009, WEB,weblink Astrobiology Top 10: Too Salty to Freeze,, December 19, 2010, In 2015 it was confirmed that perchlorate plays a role in forming recurring slope lineae on steep gullies.JOURNAL, Hecht, M. H., Kounaves, S. P., Quinn, R. C., West, S. J., Young, S. M. M., Ming, D. W., Catling, D. C., Clark, B. C., Boynton, W. V., Hoffman, J., DeFlores, L. P., Gospodinova, K., Kapit, J., Smith, P. H., Detection of Perchlorate and the Soluble Chemistry of Martian Soil at the Phoenix Lander Site, Science, 325, 5936, 64–67, 19574385, 10.1126/science.1172466, 2009Sci...325...64H, 2009, For about as far as the camera can see, the landing site is flat, but shaped into polygons between {{convert|2-3|m}} in diameter which are bounded by troughs that are {{convert|20-50|cm}} deep. These shapes are due to ice in the soil expanding and contracting due to major temperature changes. The microscope showed that the soil on top of the polygons is composed of rounded particles and flat particles, probably a type of clay.JOURNAL, Smith, P. H., Tamppari, L. K., Arvidson, R. E., Bass, D., Blaney, D., Boynton, W. V., Carswell, A., Catling, D. C., Clark, B. C., Duck, T., DeJong, E., Fisher, D., Goetz, W., Gunnlaugsson, H. P., Hecht, M. H., Hipkin, V., Hoffman, J., Hviid, S. F., Keller, H. U., Kounaves, S. P., Lange, C. F., Lemmon, M. T., Madsen, M. B., Markiewicz, W. J., Marshall, J., McKay, C. P., Mellon, M. T., Ming, D. W., Morris, R. V., Pike, W. T., Renno, N., Staufer, U., Stoker, C., Taylor, P., Whiteway, J. A., Zent, A. P., H2O at the Phoenix Landing Site, Science, 325, 5936, 58–61, 2009, 19574383, 10.1126/science.1172339, 2009Sci...325...58S, 29, Ice is present a few inches below the surface in the middle of the polygons, and along its edges, the ice is at least {{convert|8|in}} deep.Snow was observed to fall from cirrus clouds. The clouds formed at a level in the atmosphere that was around {{convert|−65|C|F K}}, so the clouds would have to be composed of water-ice, rather than carbon dioxide-ice (CO2 or dry ice), because the temperature for forming carbon dioxide ice is much lower than {{convert|−120|C|F K}}. As a result of mission observations, it is now suspected that water ice (snow) would have accumulated later in the year at this location.JOURNAL, Whiteway, J. A., Komguem, L., Dickinson, C., Cook, C., Illnicki, M., Seabrook, J., Popovici, V., Duck, T. J., Davy, R., Taylor, P. A., Pathak, J., Fisher, D., Carswell, A. I., Daly, M., Hipkin, V., Zent, A. P., Hecht, M. H., Wood, S. E., Tamppari, L. K., Renno, N., Moores, J. E., Lemmon, M. T., Daerden, F., Smith, P. H., Mars Water-Ice Clouds and Precipitation, Science, 325, 5936, 68–70, 19574386, 10.1126/science.1172344, 2009Sci...325...68W, 2009, The highest temperature measured during the mission, which took place during the Martian summer, was {{convert|−19.6|C|F K}}, while the coldest was {{convert|−97.7|C|F K}}. So, in this region the temperature remained far below the freezing point ({{convert|0|C|F K}}) of water.WEB,weblink CSA – News Release,, July 2, 2009, yes,weblink" title="">weblink July 5, 2011,

Mars Exploration Rovers

(File:Opportunity photo of Mars outcrop rock.jpg|thumb|Close-up of a rock outcrop)(File:Opp layered sol17-B017R1 br.jpg|thumb|left|Thin rock layers, not all parallel to each other)File:07-ml-3-soil-mosaic-B019R1 br.jpg|thumb|Hematite spherules ]]File:nasa mars opportunity rock water 150 eng 02mar04.jpg|thumb|Partly embedded spherules ]]The Mars Exploration Rovers, Spirit and Opportunity found a great deal of evidence for past water on Mars. The Spirit rover landed in what was thought to be a large lake bed. The lake bed had been covered over with lava flows, so evidence of past water was initially hard to detect. On March 5, 2004, NASA announced that Spirit had found hints of water history on Mars in a rock dubbed "Humphrey".WEB,weblink Mars Exploration Rover Mission: Press Releases,, March 5, 2004, As Spirit traveled in reverse in December 2007, pulling a seized wheel behind, the wheel scraped off the upper layer of soil, uncovering a patch of white ground rich in silica. Scientists think that it must have been produced in one of two ways.WEB,weblink NASA – Mars Rover Spirit Unearths Surprise Evidence of Wetter Past, NASA, May 21, 2007, One: hot spring deposits produced when water dissolved silica at one location and then carried it to another (i.e. a geyser). Two: acidic steam rising through cracks in rocks stripped them of their mineral components, leaving silica behind.WEB, Bertster, Guy, Mars Rover Investigates Signs of Steamy Martian Past, Press Release, Jet Propulsion Laboratory, Pasadena, California, December 10, 2007,weblink The Spirit rover also found evidence for water in the Columbia Hills of Gusev crater. In the Clovis group of rocks the Mössbauer spectrometer (MB) detected goethite,JOURNAL, Klingelhofer, G., etal, 2005, Lunar Planet. Sci., volume XXXVI, abstr., 2349, that forms only in the presence of water,JOURNAL, Schroder, C., etal, European Geosciences Union, General Assembly, Journal of Geophysical Research, abstr., 7, 10254, 2005, JOURNAL, Morris, S., etal, Mössbauer mineralogy of rock, soil, and dust at Gusev crater, Mars: Spirit's journal through weakly altered olivine basalt on the plains and pervasively altered basalt in the Columbia Hills, J. Geophys. Res., 111, E2, n/a, 10.1029/2005je002584, 2006JGRE..111.2S13M, 2006, JOURNAL, Ming, D., Mittlefehldt, D. W., 2006, Geochemical and mineralogical indicators for aqueous processes in the Columbia Hills of Gusev crater, Mars, J. Geophys. Res., 111, E2, E02S12, 2006JGRE..111.2S12M, Morris, R. V., Golden, D. C., Gellert, R., Yen, A., Clark, B. C., Squyres, S. W., Farrand, W. H., Ruff, S. W., Arvidson, R. E., Klingelhöfer, G., McSween, H. Y., Rodionov, D. S., Schröder, C., De Souza, P. A., Wang, A., 10.1029/2005JE002560, iron in the oxidized form Fe3+,BOOK, Bell, J, The Martian Surface, 2008, Cambridge University Press., 978-0-521-86698-9, carbonate-rich rocks, which means that regions of the planet once harbored water.JOURNAL,weblink Outcrop of long-sought rare rock on Mars found, 10.1126/science.1189667, 20522738,, June 4, 2010, Science, 329, 5990, 421–424, R. V., Morris, Ruff, S. W., Gellert, R., Ming, D. W., Arvidson, R. E., Clark, B. C., Golden, D. C., Siebach, K., Klingelhofer, G., Schroder, C., Fleischer, I., Yen, A. S., Squyres, S. W., 2010Sci...329..421M, JOURNAL, Richard V., Morris, Steven W., Ruff, Ralf, Gellert, Douglas W., Ming, Raymond E., Arvidson, Benton C., Clark, D. C., Golden, Kirsten, Siebach, Göstar, Klingelhöfer, Christian, Schröder, Iris, Fleischer, Albert S., Yen, Steven W., Squyres, 8, Identification of Carbonate-Rich Outcrops on Mars by the Spirit Rover, Science, June 3, 2010, 10.1126/science.1189667, 20522738, 329, 5990, 421–424, 2010Sci...329..421M, The Opportunity rover was directed to a site that had displayed large amounts of hematite from orbit. Hematite often forms from water. The rover indeed found layered rocks and marble- or blueberry-like hematite concretions. Elsewhere on its traverse, Opportunity investigated aeolian dune stratigraphy in Burns Cliff in Endurance Crater. Its operators concluded that the preservation and cementation of these outcrops had been controlled by flow of shallow groundwater. In its years of continuous operation, Opportunity sent back evidence that this area on Mars was soaked in liquid water in the past.WEB,weblink Opportunity Rover Finds Strong Evidence Meridiani Planum Was Wet, July 8, 2006, WEB, Harwood, William, Opportunity rover moves into 10th year of Mars operations,weblink January 25, 2013, Space Flight Now, The MER rovers found evidence for ancient wet environments that were very acidic. In fact, what Opportunity found evidence of sulphuric acid, a harsh chemical for life.JOURNAL, Benison, KC, Laclair, DA, Modern and ancient extremely acid saline deposits: terrestrial analogs for martian environments?, Astrobiology, 3, 3, 609–618, 2003, 14678669, 10.1089/153110703322610690, 2003AsBio...3..609B, JOURNAL, Benison, K, Bowen, B, Acid saline lake systems give clues about past environments and the search for life on Mars, Icarus, 183, 1, 225–229, 2006Icar..183..225B, 2006, 10.1016/j.icarus.2006.02.018, But on May 17, 2013, NASA announced that Opportunity found clay deposits that typically form in wet environments that are near neutral acidity. This find provides additional evidence about a wet ancient environment possibly favorable for life.

Mars Reconnaissance Orbiter

File:Springs in Vernal Crater.jpg|left|thumb|Springs in Vernal Crater, as seen by HIRISE. These springs may be good places to look for evidence of past life, because hot springs can preserve evidence of life forms for a long time. Location is Oxia Palus quadrangleOxia Palus quadrangleThe Mars Reconnaissance Orbiter's HiRISE instrument has taken many images that strongly suggest that Mars has had a rich history of water-related processes. A major discovery was finding evidence of ancient hot springs. If they have hosted microbial life, they may contain biosignatures.JOURNAL, 10.1126/science.1150690, Osterloo, MM, Hamilton, 2008, VE, Bandfield, JL, Glotch, TD, Baldridge, AM, Christensen, PR, Tornabene, LL, Anderson, FS, Chloride-Bearing Materials in the Southern Highlands of Mars, Science, 319, 5870, 1651–1654, 18356522, 2008Sci...319.1651O,, Research published in January 2010, described strong evidence for sustained precipitation in the area around Valles Marineris.JOURNAL, 10.1016/j.icarus.2009.04.017, Weitz, C., Milliken, 2010, R.E., Grant, J.A., McEwen, A.S., Williams, R.M.E., Bishop, J.L., Thomson, B.J., Mars Reconnaissance Orbiter observations of light-toned layered deposits and associated fluvial landforms on the plateaus adjacent to Valles Marineris, Icarus, 205, 1, 73–102, 2010Icar..205...73W, JOURNAL, Atmospheric mass loss by stellar wind from planets around main sequence M stars, 210, 2, 539–1000, December 2010, 10.1016/j.icarus.2010.07.013, 2010Icar..210..539Z, Icarus, Zendejas, J., Segura, A., Raga, A.C., 1006.0021, The types of minerals there are associated with water. Also, the high density of small branching channels indicates a great deal of precipitation.Rocks on Mars have been found to frequently occur as layers, called strata, in many different places.JOURNAL, Grotzinger, J., R., Milliken, 2012, Sedimentary Geology of Mars, SEPM, Layers form by various ways, including volcanoes, wind, or water.WEB,weblink HiRISE – High Resolution Imaging Science Experiment, HiriUniversity of Arizona, December 19, 2010, Light-toned rocks on Mars have been associated with hydrated minerals like sulfates and clay.WEB,weblink Target Zone: Nilosyrtis? | Mars Odyssey Mission THEMIS,, December 19, 2010, File:Asimov Layers Close-up.JPG|thumb|Layers on the west slope of Asimov Crater. Location is Noachis quadrangleNoachis quadrangleThe orbiter helped scientists determine that much of the surface of Mars is covered by a thick smooth mantle that is thought to be a mixture of ice and dust.JOURNAL, Head, James W., Mustard, John F., Kreslavsky, Mikhail A., Milliken, Ralph E., Marchant, David R., Recent ice ages on Mars, Nature, 426, 6968, 797–802, 2003, 14685228, 10.1038/nature02114, 2003Natur.426..797H, JOURNAL, Mellon, M. T., B. M., Jakosky, S. E., Postawko, 1997, The persistence of equatorial ground ice on Mars,, J. Geophys. Res., 102(E8), E8, 19357–19369, 10.1029/97JE01346, 1997JGR...10219357M, WEB, John D., Arfstrom,weblink A Conceptual Model of Equatorial Ice Sheets on Mars. J, Lunar and Planetary Institute, Comparative Climatology of Terrestrial Planets, 2012, The ice mantle under the shallow subsurface is thought to result from frequent, major climate changes. Changes in Mars' orbit and tilt cause significant changes in the distribution of water ice from polar regions down to latitudes equivalent to Texas. During certain climate periods water vapor leaves polar ice and enters the atmosphere. The water returns to the ground at lower latitudes as deposits of frost or snow mixed generously with dust. The atmosphere of Mars contains a great deal of fine dust particles. Water vapor condenses on the particles, then they fall down to the ground due to the additional weight of the water coating. When ice at the top of the mantling layer goes back into the atmosphere, it leaves behind dust, which insulates the remaining ice.NEWS, MLA NASA/Jet Propulsion Laboratory, December 18, 2003, Mars may be emerging from an ice age, ScienceDaily,weblink In 2008, research with the Shallow Radar on the Mars Reconnaissance Orbiter provided strong evidence that the lobate debris aprons (LDA) in Hellas Planitia and in mid northern latitudes are glaciers that are covered with a thin layer of rocks. Its radar also detected a strong reflection from the top and base of LDAs, meaning that pure water ice made up the bulk of the formation. The discovery of water ice in LDAs demonstrates that water is found at even lower latitudes.BOOK, Hugh H., Kieffer, Mars,weblink March 7, 2011, 1992, University of Arizona Press, 978-0-8165-1257-7, Research published in September 2009, demonstrated that some new craters on Mars show exposed, pure water ice.JOURNAL, Byrne, 19779195, 2009, Shane, Dundas, Colin M., Kennedy, Megan R., Mellon, Michael T., McEwen, Alfred S., Cull, Selby C., Daubar, Ingrid J., Shean, David E., Seelos, Kimberly D., Murchie, Scott L., Cantor, Bruce A., Arvidson, Raymond E., Edgett, Kenneth S., Reufer, Andreas, Thomas, Nicolas, Harrison, Tanya N., Posiolova, Liliya V., Seelos, Frank P., Distribution of mid-latitude ground ice on Mars from new impact craters, Science, 325, 5948, 1674–1676, 10.1126/science.1175307, 2009Sci...325.1674B, After a time, the ice disappears, evaporating into the atmosphere. The ice is only a few feet deep. The ice was confirmed with the Compact Imaging Spectrometer (CRISM) on board the Mars Reconnaissance Orbiter.WEB,weblink Water Ice Exposed in Mars Craters,, December 19, 2010, Additional collaborating reports published in 2019 evaluated the amount of water ice located at the northern pole. One report used data from the MRO's SHARAD (SHAllow RADar sounder) probes. SHARAD has the capability scanning up to about {{convert|2|km|miles}} below the surface at {{convert|15|m|ft}} intervals. The analysis of past SHARAD runs showed evidence of strata of water ice and sand below the Planum Boreum, with as much as 60% to 88% of the volume being water ice. This supports the theory of the long-term global weather of Mars consisting of cycles of global warming and cooling; during cooling periods, water gathered at the poles to form the ice layers, and then as global warming occurred, the unthawed water ice was covered by dust and dirt from Mars' frequent dust storms. The total ice volume determine by this study indicated that there was approximately {{convert|2.2e5|km3|cumi}}, or enough water, if melted, to fully cover the Mars surface with a {{convert|1.5|m|ft}} layer of water.JOURNAL, Buried ice and sand caps at the north pole of Mars: revealing a record of climate change in the cavi unit with SHARAD, S. Nerozzi, J.W. Holt, May 22, 2019, 10.1029/2019GL082114, Geophysical Research Letters, 46, 13, 7278, 2019GeoRL..46.7278N, The work was corroborated by a separate study that used recorded gravity data to estimate the density of the Planum Boreum, indicating that on average, it contained up to 55% by volume of water ice.JOURNAL, Compositional Constraints on the North Polar Cap of Mars from Gravity and Topography, Lujendra Ojha, Stefano Nerozzi, Kevin Lewis, May 22, 2019, 10.1029/2019GL082294, Geophysical Research Letters, {{Clear}}

Curiosity rover

File:PIA16156-Mars Curiosity Rover-Water-AncientStreambed.jpg|thumb|left|"Hottah" rock outcrop – an ancient streambed discovered by the (Curiosity (rover)|Curiosity rover]] team (September 14, 2012) (close-up) (3-D version).)File:PIA16189 fig1-Curiosity Rover-Rock Outcrops-Mars and Earth.jpg|thumb|Rock outcrop on Mars – compared with a terrestrial fluvial conglomerate – suggesting water "vigorously" flowing in a stream.WEB, Brown, Dwayne, Cole, Steve, Webster, Guy, Agle, D.C., NASA Rover Finds Old Streambed On Martian Surface,weblink September 27, 2012, NASA, WEB, NASA, NASA, NASA's Curiosity Rover Finds Old Streambed on Mars – video (51:40),weblink September 27, 2012, NASANASAVery early in its ongoing mission, NASA's Curiosity rover discovered unambiguous fluvial sediments on Mars. The properties of the pebbles in these outcrops suggested former vigorous flow on a streambed, with flow between ankle- and waist-deep. These rocks were found at the foot of an alluvial fan system descending from the crater wall, which had previously been identified from orbit.In October 2012, the first X-ray diffraction analysis of a Martian soil was performed by Curiosity. The results revealed the presence of several minerals, including feldspar, pyroxenes and olivine, and suggested that the Martian soil in the sample was similar to the weathered basaltic soils of Hawaiian volcanoes. The sample used is composed of dust distributed from global dust storms and local fine sand. So far, the materials Curiosity has analyzed are consistent with the initial ideas of deposits in Gale Crater recording a transition through time from a wet to dry environment.WEB, Brown, Dwayne, NASA Rover's First Soil Studies Help Fingerprint Martian Minerals,weblink October 30, 2012, NASA, In December 2012, NASA reported that Curiosity performed its first extensive soil analysis, revealing the presence of water molecules, sulfur and chlorine in the Martian soil.WEB, Brown, Dwayne, Webster, Guy, Neal-Jones, Nance, NASA Mars Rover Fully Analyzes First Martian Soil Samples,weblink December 3, 2012, NASA, WEB, Chang, Ken, Mars Rover Discovery Revealed,weblink December 3, 2012, New York Times, And in March 2013, NASA reported evidence of mineral hydration, likely hydrated calcium sulfate, in several rock samples including the broken fragments of "Tintina" rock and "Sutton Inlier" rock as well as in veins and nodules in other rocks like "Knorr" rock and "Wernicke" rock.WEB, Webster, Guy, Brown, Dwayne, Curiosity Mars Rover Sees Trend In Water Presence,weblink March 18, 2013, NASA, WEB, Rincon, Paul, Curiosity breaks rock to reveal dazzling white interior,weblink March 19, 2013, BBC, WEB, Staff, Red planet coughs up a white rock, and scientists freak out,weblink March 20, 2013, MSN, yes,weblink" title="">weblink March 23, 2013, Analysis using the rover's DAN instrument provided evidence of subsurface water, amounting to as much as 4% water content, down to a depth of {{convert|60|cm|ft|abbr=on}}, in the rover's traverse from the Bradbury Landing site to the Yellowknife Bay area in the Glenelg terrain.On September 26, 2013, NASA scientists reported the Mars Curiosity rover detected abundant chemically-bound water (1.5 to 3 weight percent) in soil samples at the Rocknest region of Aeolis Palus in Gale Crater.WEB, Lieberman, Josh, Mars Water Found: Curiosity Rover Uncovers 'Abundant, Easily Accessible' Water In Martian Soil,weblink September 26, 2013, iSciencetimes, JOURNAL, Leshin, L. A., etal, Volatile, Isotope, and Organic Analysis of Martian Fines with the Mars Curiosity Rover, September 27, 2013, Science (journal), Science, 341, 6153, 10.1126/science.1238937, 1238937, 24072926, 2013Sci...341E...3L, JOURNAL, Grotzinger, John, Introduction To Special Issue: Analysis of Surface Materials by the Curiosity Mars Rover, September 26, 2013, Science (journal), Science, 341, 6153, 1475, 10.1126/science.1244258, 24072916, 2013Sci...341.1475G, WEB, Neal-Jones, Nancy, Zubritsky, Elizabeth, Webster, Guy, Martialay, Mary, Curiosity's SAM Instrument Finds Water and More in Surface Sample,weblink September 26, 2013, NASA, WEB, Webster, Guy, Brown, Dwayne, Science Gains From Diverse Landing Area of Curiosity,weblink September 26, 2013, NASA, NEWS, Chang, Kenneth, Hitting Pay Dirt on Mars,weblink October 1, 2013, New York Times, In addition, NASA reported the rover found two principal soil types: a fine-grained mafic type and a locally derived, coarse-grained felsic type.JOURNAL, Meslin, P.-Y., etal, Soil Diversity and Hydration as Observed by ChemCam at Gale Crater, Mars, September 26, 2013, Science (journal), Science, 341, 6153, 10.1126/science.1238670, 1238670, 24072924, 2013Sci...341E...1M, The mafic type, similar to other martian soils and martian dust, was associated with hydration of the amorphous phases of the soil. Also, perchlorates, the presence of which may make detection of life-related organic molecules difficult, were found at the Curiosity rover landing site (and earlier at the more polar site of the Phoenix lander) suggesting a "global distribution of these salts". NASA also reported that Jake M rock, a rock encountered by Curiosity on the way to Glenelg, was a mugearite and very similar to terrestrial mugearite rocks.JOURNAL, Stolper, E.M., Baker, M.B., Newcombe, M.E., Schmidt, M.E., Treiman, A.H., Cousin, A., Dyar, M.D., Fisk, M.R., Gellert, R., King, P.L., Leshin, L., Maurice, S., McLennan, S.M., Minitti, M.E., Perrett, G., Rowland, S., Sautter, V., Wiens, R.C., MSL ScienceTeam, The Petrochemistry of Jake_M: A Martian Mugearite, Science (journal), Science, 341, 6153, 10.1126/science.1239463, American Association for the Advancement of Science, AAAS, 2013, 1239463, 24072927, 2013Sci...341E...4S,weblink On December 9, 2013, NASA reported that Mars once had a large freshwater lake inside Gale Crater, that could have been a hospitable environment for microbial life.On December 16, 2014, NASA reported detecting an unusual increase, then decrease, in the amounts of methane in the atmosphere of the planet Mars; in addition, organic chemicals were detected in powder drilled from a rock by the Curiosity rover. Also, based on deuterium to hydrogen ratio studies, much of the water at Gale Crater on Mars was found to have been lost during ancient times, before the lakebed in the crater was formed; afterwards, large amounts of water continued to be lost.WEB, Webster, Guy, Neal-Jones, Nancy, Brown, Dwayne, NASA Rover Finds Active and Ancient Organic Chemistry on Mars,weblink December 16, 2014, NASA, December 16, 2014, NEWS, Chang, Kenneth, 'A Great Moment': Rover Finds Clue That Mars May Harbor Life,weblink December 16, 2014, New York Times, December 16, 2014, JOURNAL, Mars Atmosphere – The imprint of atmospheric evolution in the D/H of Hesperian clay minerals on Mars, December 16, 2014, Science (journal), Science, 347, 6220, 412–414, 10.1126/science.1260291, 1, Mahaffy, P. R., Webster, C. R., Stern, J. C., Brunner, A. E., Atreya, S. K., Conrad, P. G., Domagal-Goldman, S., Eigenbrode, J. L., Flesch, G. J., Christensen, L. E., Franz, H. B., Freissinet, C., Glavin, D. P., Grotzinger, J. P., Jones, J. H., Leshin, L. A., Malespin, C., McAdam, A. C., Ming, D. W., Navarro-Gonzalez, R., Niles, P. B., Owen, T., Pavlov, A. A., Steele, A., Trainer, M. G., Williford, K. H., Wray, J. J., 2015Sci...347..412M, 25515119,weblink On April 13, 2015, Nature published an analysis of humidity and ground temperature data collected by Curiosity, showing evidence that films of liquid brine water form in the upper 5 cm of Mars's subsurface at night. The water activity and temperature remain below the requirements for reproduction and metabolism of known terrestrial microorganisms.NEWS, Rincon, Paul,weblink Evidence of liquid water found on Mars, BBC News, April 13, 2015, April 15, 2015, On October 8, 2015, NASA confirmed that lakes and streams existed in Gale crater 3.3 – 3.8 billion years ago delivering sediments to build up the lower layers of Mount Sharp.WEB, Clavin, Whitney, NASA's Curiosity Rover Team Confirms Ancient Lakes on Mars,weblink October 8, 2015, NASA, October 9, 2015, JOURNAL, Grotzinger, J.P., Deposition, exhumation, and paleoclimate of an ancient lake deposit, Gale crater, Mars, October 9, 2015, Science (journal), Science, 350, 6257, aac7575, 10.1126/science.aac7575, 26450214, 2015Sci...350.7575G, On November 4, 2018, geologists presented evidence, based on studies in Gale Crater by the Curiosity rover, that there was plenty of water on early Mars.NEWS, Geological Society of America, Evidence of outburst flooding indicates plentiful water on early Mars,weblink November 3, 2018, EurekAlert!, November 5, 2018, Geological Society of America, JOURNAL, Heydari, Ezat, etal, Significance of Flood Depositis in Gale Crater, Mars,weblink November 4, 2018, Geological Society of America, November 5, 2018,

Mars Express

The Mars Express Orbiter, launched by the European Space Agency, has been mapping the surface of Mars and using radar equipment to look for evidence of sub-surface water. Between 2012 and 2015, the Orbiter scanned the area beneath the ice caps on the Planum Australe. Scientists determined by 2018 that the readings indicated a sub-surface lake bearing water about {{convert|20|km|mi}} wide. The top of the lake is located {{convert|1.5|km}} under the planet's surface; how much deeper the liquid water extends remains unknown.JOURNAL, Orosei R, Lauro SE, Pettinelli E, Cicchetti A, Coradini M, Cosciotti B, Di Paolo F, Flamini E, Mattei E, Pajola M, Soldovieri F, Cartacci M, Cassenti F, Frigeri A, Giuppi S, Martufi R, Masdea A, Mitri G, Nenna C, Noschese R, Restano M, Seu R, July 25, 2018, Radar evidence of subglacial liquid water on Mars, Science (journal), Science, 361, 3699, 490–493, 10.1126/science.aar7268, 30045881, 2018Sci...361..490O, 11573/1148029, WEB,weblink Liquid water 'lake' revealed on Mars, Mary, Halton, July 25, 2018, July 25, 2018, BBC News,

Interactive map

{{Mars map}}

See also

{{div col|colwidth=30em}} {{div col end}}




  • Boyce, Joseph, M. (2008). The Smithsonian Book of Mars; Konecky & Konecky: Old Saybrook, CT, {{ISBN|978-1-58834-074-0}}
  • Carr, Michael, H. (1996). Water on Mars; Oxford University Press: New York, {{ISBN|0-19-509938-9}}.
  • Carr, Michael, H. (2006). The Surface of Mars; Cambridge University Press: Cambridge, UK, {{ISBN|978-0-521-87201-0}}.
  • Hartmann, William, K. (2003). A Traveler’s Guide to Mars: The Mysterious Landscapes of the Red Planet; Workman: New York, {{ISBN|0-7611-2606-6}}.
  • Hanlon, Michael (2004). The Real Mars: Spirit, Opportunity, Mars Express and the Quest to Explore the Red Planet; Constable: London, {{ISBN|1-84119-637-1}}.
  • Kargel, Jeffrey, S. (2004). Mars: A Warmer Wetter Planet; Springer-Praxis: London, {{ISBN|1-85233-568-8}}.
  • Morton, Oliver (2003). Mapping Mars: Science, Imagination, and the Birth of a World; Picador: New York, {{ISBN|0-312-42261-X}}.
  • Sheehan, William (1996). The Planet Mars: A History of Observation and Discovery; University of Arizona Press: Tucson, AZ, {{ISBN|0-8165-1640-5}}.
  • Viking Orbiter Imaging Team (1980). Viking Orbiter Views of Mars, C.R. Spitzer, Ed.; NASA SP-441: Washington DC.

External links

{{Commons|Water on Mars}} {{Mars}}{{Geography of Mars}}

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