Mars contains water, though mostly as subsurface permafrost. Surface water is readily visible at some places, such as the ice-filled Korolev Crater, near the north polar ice cap.
Although very small amounts of liquid water may occur transiently on the surface of Mars, limited to traces of dissolved moisture from the atmosphere and thin films,[1][2][3] large quantities of ice are present on and under the surface. Small amounts of water vapor are present in the atmosphere, and liquid water may be present under the surface. In addition, a large quantity of liquid water was likely present on the surface in the distant past. Currently, ice is mostly present in polarpermafrost.
[4] More than 5 million km3 of ice have been detected at or near the surface of Mars, enough to cover the planet to a depth of 35 meters (115 ft).[5] Even more ice might be locked away in the deep subsurface.[6][7] The chemical signature of water vapor on Mars was first unequivocally demonstrated in 1963 by spectroscopy using an Earth-based telescope. In 2008 and 2013, ice was detected in soil samples taken by the Phoenix lander and Curiosity rover. In 2018, radar findings suggested the presence of liquid water in subglacial lakes and in 2024, seismometer data suggested the presence of liquid water deep under the surface.
Most of the ice on Mars is buried. However, ice is present at the surface at several locations. In the mid-latitudes, surface ice is present in impact craters, steep scarps and gullies.[8][9][10] At latitudes near the poles, ice is present in glaciers. Ice is visible at the surface at the north polar ice cap,[11] and abundant ice is present beneath the permanent carbon dioxide ice cap at the Martian south pole.
The present-day inventory of water on Mars can be estimated from spacecraft images, remote sensing techniques (spectroscopic measurements,[12][13]ground-penetrating radar,[14] etc.), and surface investigations from landers and rovers including x-ray spectroscopy, neutron spectroscopy and seismography.[15][16]
Although the surface of Mars was periodically wet and could have been hospitable to microbial life billions of years ago,[56] no definite evidence of life, past or present, has been found on Mars.[57][58] The best potential locations for discovering life on Mars may be in subsurface environments.[59][60][61] A large amount of underground ice, equivalent to the volume of water in Lake Superior, has been found under Utopia Planitia.[62][63][64] In 2018, based on radar data, scientists reported the discovery of a possible subglacial lake on Mars, 1.5 km (0.93 mi) below the southern polar ice cap, with a horizontal extent of about 20 km (12 mi),[65][66] findings that were strengthened by additional radar findings in September 2020,[67][68] but subsequent work has questioned this detection.[69][70]
In August 2024, researchers reported that analysis of seismic data from NASA's InSight Mars Lander suggested the presence of a reservoir of liquid water at depths of 10–20 kilometres (6.2–12.4 mi) under the Martian crust.[72]
^ abOjha, 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. 8 (11): 829–832. Bibcode:2015NatGe...8..829O. doi:10.1038/ngeo2546. S2CID59152931.
^Jakosky, B. M.; Haberle, R.M. (1992). "The Seasonal Behavior of Water on Mars". In Kieffer, H. H.; et al. (eds.). Mars. Tucson, Arizona: University of Arizona Press. pp. 969–1016.
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^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. Bibcode:1991Natur.352..589B. doi:10.1038/352589a0. S2CID4321529.
^Dohm, J. M.; Baker, Victor R.; 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. (2009). "GRS Evidence and the Possibility of Paleooceans on Mars"(PDF). Planetary and Space Science. 57 (5–6): 664–684. Bibcode:2009P&SS...57..664D. doi:10.1016/j.pss.2008.10.008. Archived from the original(PDF) on September 22, 2017. Retrieved July 23, 2019.
^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. Bibcode:2001Icar..154...40C. doi:10.1006/icar.2001.6671. S2CID13694518.
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^Fassett, C. I.; Dickson, James L.; Head, James W.; Levy, Joseph S.; Marchant, David R. (2010). "Supraglacial and Proglacial Valleys on Amazonian Mars". Icarus. 208 (1): 86–100. Bibcode:2010Icar..208...86F. doi:10.1016/j.icarus.2010.02.021.
^Heisinger, H.; Head, J. (2002). "Topography and morphology of the Argyre basin, Mars: implications for its geologic and hydrologic history". Planetary and Space Science. 50 (10–11): 939–981. Bibcode:2002P&SS...50..939H. doi:10.1016/S0032-0633(02)00054-5.
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^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. Bibcode:2008Icar..198...37F. doi:10.1016/j.icarus.2008.06.016.
^Head, J.; Marchant, D. (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 and Planetary Science. 37: 1128.
^Head, J.; Marchant, D. (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". Lunar and Planetary Science. 37: 1127.
^Martín-Torres, F. Javier; Zorzano, María-Paz; Valentín-Serrano, Patricia; Harri, Ari-Matti; Genzer, Maria (April 13, 2015). "Transient liquid water and water activity at Gale crater on Mars". Nature Geoscience. 8 (5): 357–361. Bibcode:2015NatGe...8..357M. doi:10.1038/ngeo2412.
^Dartnell, L. R.; Desorgher, L.; Ward, J. M.; Coates, A. J. (2007). "Martian sub-surface ionising radiation: biosignatures and geology"(PDF). Biogeosciences. 4 (4): 545–558. Bibcode:2007BGeo....4..545D. doi:10.5194/bg-4-545-2007. Archived(PDF) from the original on July 9, 2014. Retrieved September 1, 2019. 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.
^de Morais, A. (2012). "A Possible Biochemical Model for Mars"(PDF). 43rd Lunar and Planetary Science Conference. Archived(PDF) from the original on July 6, 2021. Retrieved 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.
^Didymus, JohnThomas (January 21, 2013). "Scientists find evidence Mars subsurface could hold life". Digital Journal – Science. Archived from the original on December 13, 2013. Retrieved June 16, 2013. 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.
^Steigerwald, Bill (January 15, 2009). "Martian Methane Reveals the Red Planet is not a Dead Planet". NASA's Goddard Space Flight Center. NASA. Archived from the original on January 17, 2009. Retrieved June 16, 2013. 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