Groundwater on Mars

Rain and snow were regular occurrences on Mars in the past; especially in the Noachian and early Hesperian epochs. Water was theorized to seep into the ground until it reached a formation that would not allow it to penetrate further (such a layer is called an aquitard and is believed to be impermeable). Water then accumulated forming a saturated layer. Deep aquifers may still exist.

Overviews

Researchers hypothesize, based on geological surface features of Mars and the results of numerical simulations, that several prominent features on the planet have been produced by the action of groundwater and that Mars may have had a planet-wide groundwater system. When water rose to the surface or near the surface, various minerals were deposited and sediments became cemented together. Some of the minerals were sulfates that were probably produced when water dissolved sulfur from underground rocks, and then became oxidized when it came into contact with the air. While traveling through the aquifer, the water passed through igneous rock basalt, which would have contained sulfur. In an aquifer, water occupies open space (pore space) that lies between rock particles. This layer would spread out, eventually coming to be under most of the Martian surface. The top of this layer is called the water table. Calculations show that the water table on Mars was for a time 600 meters below the surface. In September 2019, the InSight lander uncovered unexplained magnetic pulses, and magnetic oscillations consistent with an existing reservoir of liquid water deep underground. Researchers have concluded that Gale Crater has experienced many episodes of groundwater surge with changes in the groundwater chemistry. These chemical changes could support life.

2024 finding In August 2024, a new analysis of data suggested the presence of liquid water on Mars, trapped in tiny cracks and pores of rock deep in the outer crust of the planet. The findings came from NASA's InSight lander, which recorded four years' of Mars quakes. The analysis suggested the presence of water at depths of about six to 12 miles (10 to 20 km) below the Martian surface. The seismometer only took measurements from directly below the InSight lander. However, the researchers concluded that if the findings are representative of the rest of the Martian crust, there may be enough water in the crust to fill oceans up to a depth of 1 mile (1.6 km) on the planet's surface.

Layered terrain

Some locations on Mars show groups of layered rocks. Rock layers are present under the resistant caps of pedestal craters, on the floors of many large impact craters, and in the area called Arabia. In some places the layers are arranged into regular patterns. It has been suggested that the layers were put into place by volcanoes, the wind, or by being at the bottom of a lake or sea. Calculations and simulations show that groundwater carrying dissolved minerals would surface in the same locations that have abundant rock layers. According to these ideas, deep canyons and large craters would receive water coming from the ground. Many craters in the Arabia area of Mars contain groups of layers. Some of these layers may have resulted from climate change. The tilt of the rotational axis of Mars has repeatedly changed in the past. Some changes are large. Because of these variations of climate, at times the atmosphere of Mars would have been much thicker and contained more moisture. The amount of atmospheric dust also has increased and decreased. It is believed that these frequent changes helped to deposit material in craters and other low places. The rising of mineral-rich ground water cemented these materials. The model also predicts that after a crater is full of layered rocks, additional layers will be laid down in the area around the crater. So, the model predicts that layers may also have formed in intercrater regions; layers in these regions have been observed. Layers can be hardened by the action of groundwater. Martian ground water probably moved hundreds of kilometers, and in the process it dissolved many minerals from the rock it passed through. When ground water surfaces in low areas containing sediments, water evaporates in the thin atmosphere and leaves behind minerals as deposits and/or cementing agents. Consequently, layers of dust could not later easily erode away since they were cemented together. On Earth, mineral-rich waters often evaporate forming large deposits of various types of salts and other minerals. Sometimes water flows through Earth's aquifers, and then evaporates at the surface just as is hypothesized for Mars. One location this occurs on Earth is the Great Artesian Basin of Australia. On Earth the hardness of many sedimentary rocks, like sandstone, is largely due to the cement that was put in place as water passed through. In February 2019, European scientists published geological evidence of an ancient planet-wide groundwater system that was, arguably, connected to a putative vast ocean.

Layers in Crommelin crater

Layers in Danielson crater

Inverted terrain Many areas on Mars show inverted relief. In those places, former stream channels are displayed as raised beds, instead of stream valleys. Raised beds form when old stream channels become filled with material that is resistant to erosion. After later erosion removes surrounding soft materials, more resistant materials that were deposited in the stream bed are left behind. Lava is one substance that can flow down valleys and produce such inverted terrain. However, fairly loose materials can get quite hard and erosion resistant when cemented by minerals. These minerals can come from groundwater. It is thought that a low point, like a valley focuses groundflow, so more water and cements move into it, and this results in a greater degree of cementation. Terrain inversion can also happen without cementation by groundwater, however. If a surface is being eroded by wind, the necessary contrast in erodibility can arise simply from variations in grain size of loose sediments. Since wind can carry away sand but not cobbles, for example, a channel bed rich in cobbles could form an inverted ridge if it was originally surrounded by much finer sediments, even if the sediments were not cemented. This effect has been invoked for channels in Saheki crater. Places on Mars that contain layers in the bottoms of craters often also have inverted terrain.

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