page_title: Water on Mars
section_title: Mars Reconnaissance Orbiter
hierarchical_section_title: Water on Mars / Findings by probes / Mars Reconnaissance Orbiter
caption_attribution_description: English: hydrothrmal springs in vernal crater, as seen by hirise. Location is 5.6 degrees north latitude and 4.4 degrees west longitude. Image was taken by the Mars Reconnaissance Orbiter's HiRISE. The HiRISE camera was built by Ball Aerospace and Technology orporation and is operated by the University of Arizona. Image courtesy NASA/JPL/University of Arizona.
context_page_description: Almost all water on Mars today exists as ice, though it also exists in small quantities as vapor in the atmosphere. What was thought to be low-volume liquid brines in shallow Martian soil, also called recurrent slope lineae, may be grains of flowing sand and dust slipping downhill to make dark streaks. The only place where water ice is visible at the surface is at the north polar ice cap. 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. 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 35 meters. Even more ice is likely to be locked away in the deep subsurface.
  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.
context_section_description: The 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. Research published in January 2010, described strong evidence for sustained precipitation in the area around Valles Marineris. 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. Layers form by various ways, including volcanoes, wind, or water. Light-toned rocks on Mars have been associated with hydrated minerals like sulfates and clay.
  The 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.
  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.
  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.
  Research published in September 2009, demonstrated that some new craters on Mars show exposed, pure water ice. 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.
  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 2 kilometres (1.2 mi) below the surface at 15 metres (49 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 2.2×10⁵ cubic kilometres (5.3×10⁴ cu mi), or enough water, if melted, to fully cover the Mars surface with a 1.5 metres (4.9 ft) layer of water. 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.
  Many features that look like the pingos on the Earth were found in Utopia Planitia (~35-50° N; ~80-115° E) by examining photos from HiRISE. Pingos contain a core of ice.
caption: 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 quadrangle.
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