Martian Hydrology

 

Figure 1 Perspective view of crater with water ice at Martian north pole.

Due to the low atmospheric pressure on Mars' surface, liquid water can only exist at the lowest elevations for short periods of time. Water appears to make up the majority of the two polar ice caps. If the water ice in the south polar ice cap were to melt, it would cover the entire planet's surface to a depth of 11 meters. The permafrost mantle reaches from the pole to around 60 ° latitude.

Large amounts of water ice are believed to be trapped within Mars' thick cryosphere. Radar images from Mars Express and the Mars Reconnaissance Orbiter reveal huge amounts of water ice at both the poles and mid-latitudes from July 2005 to November 2008. On July 31, 2008, the Phoenix lander took a direct sample of water ice in shallow Martian soil.

Figure 2 The north pole of Mars at the summer solstice, as seen in an image shot by the European Space Agency's Mars Express in May 2010.

Landforms visible on Mars clearly suggest that liquid water existed on the planet's surface at some point. Outflow channels, which are large linear swaths of scoured earth, cut across the surface in roughly 25 spots. These structures are thought to record erosion that occurred during the catastrophic discharge of water from subterranean aquifers, however some of them have also been attributed to glaciers or lava. Ma'adim Vallis, for example, is 700 kilometers long and far wider than the Grand Canyon, with a breadth of 20 kilometers and a depth of 2 kilometers in some spots. It is assumed that rushing water carved it early in Mars' history. Only a few million years ago, the youngest of these channels were considered to have formed. Finer-scale, dendritic networks of valleys are distributed across considerable swaths of the topography elsewhere on the Martian surface, notably in the oldest areas. The characteristics of these valleys, as well as their location, strongly suggest that they were carved by runoff caused by rain or snow in early Mars history. Although subsurface water flow and groundwater sapping may play key supporting roles in some networks, precipitation was nearly always the primary cause of the incision.

Thousands of features similar to terrestrial gullies can be found along crater and canyon walls. The gullies are found in the southern hemisphere's highlands, facing the Equator, and are all poleward of 30 degrees latitude. Several scientists have indicated that their development process requires liquid water, most likely from melting ice, while others have proposed formation mechanisms utilizing carbon dioxide frost or dry dust movement. Weathering has left no partially degraded gullies and no overlaid impact craters, indicating that these are relatively young structures, potentially even active today.

Other geological features, such as deltas and alluvial fans preserved in craters, also strongly suggest that Mars was warmer and wetter at some point in its history. Such circumstances necessitate the widespread presence of crater lakes across a considerable percentage of the surface, which is supported by independent mineralogical, sedimentological, and geomorphological evidence. Some authors have even claimed that during the planet's history, much of the planet's low northern plains were covered by a genuine ocean hundreds of meters deep, however, this is still debatable.

Figure 3 Ice adjacent to Martian dunes.

The discovery of specific minerals such as hematite and goethite, both of which develop in the presence of water, adds to the evidence that liquid water once existed on Mars' surface. Higher resolution analyses by the Mars Reconnaissance Orbiter have refuted some of the data previously thought to imply ancient water basins and flows. The mineral jarosite was discovered by Opportunity in 2004. This only occurs in the presence of acidic water, indicating that there was once water on Mars. More recent evidence for liquid water comes from NASA's Mars rover Opportunity's discovery of the mineral gypsum on the surface in December 2011. Furthermore, according to study leader Francis McCubbin, a planetary scientist at the University of New Mexico in Albuquerque who studied hydroxals in crystalline minerals from Mars, the amount of water in Mars' upper mantle is equal to or greater than that of Earth, with 50–300 parts per million of water, enough to cover the entire planet to a depth of 200–1000 meters.

On March 18, 2013, NASA reported evidence of mineral hydration, most likely hydrated calcium sulphate, in several rock samples, including broken fragments of "Tintina" rock and "Sutton Inlier" rock, as well as veins and nodules in other rocks such as "Knorr" rock and "Wernicke" rock, from instruments on the Curiosity rover. In the rover's traverse from the Bradbury Landing site to the Yellowknife Bay area in the Glenelg terrain, analysis using the rover's DAN instrument revealed evidence of subsurface water with as much as 4% water content down to a depth of 60 cm (2.0 ft).