Water beneath the Martian surface
Astronomers have found more evidence that Mars was wet and warm in the ancient past, but the discovery comes with a twist: The water may have flowed below the Martian surface, rather than on top of it.
The new study, which analyzed clay deposits on the Red Planet, revealed that thesurface of Mars may have been dry and arid even in its distant past, with lakes and rivers dotting the Martian landscape for only brief periods.
Water-carved landforms on Mars are just one source of evidence that liquid once existed on the planet. Orbiting satellites have also found beds of clay, created by chemical interactions between volcanic rock and water.
A team of planetary scientists, led by Bethany Ehlmann of California Institute of Technology, examined a decades worth of images taken by the European Space Agencys (ESA) Mars Express and NASAs Mars Reconnaissance Orbiter, searching for clay deposits.
Because different conditions give rise to different chemical changes in the same material, clay can be a distinctive record of the environment that shaped it.
Their findings could help solve the mystery of where the water on Mars has gone.
Mixing up Martian clay
Terrestrial clays form when water runs across various minerals, weathering and mixing them together as it carries them along. Many Martian clay beds, found near features such as dry river and lake beds, likely have a similar origin, indicating running water existed at some point .
But a wetter Mars begs a question where did all of the water go? The Martian atmosphere today is too thin to hold water on the planets surface, so scientists have theorized that its atmosphere was thicker in the past.
Some of the water may have been trapped in carbonate rocks or ice, as well. But current estimates dont account for all of the water lost, and the frozen formations just dont hold enough.
All clays arent formed by rushing rivers, however. On Earth, melted snow and groundwater flow through underground volcanic rocks, heating it and causing the two to chemically interact to form clay. Hidden beneath the Martian surface, these crustal clays show up in heavily eroded areas or via crater impacts.
A third type of clay is created by the intense weathering of volcanic-formed basaltic rock. While river-formed surface clay tends to be found in low-laying basins (since the water runs downhill), these weathered clays are created at higher altitudes.
Ehlmann and her team found evidence of all three types of clay on Mars, but the underground clay dominated.
The most stable,
long-lasting, clay-forming environment was in the subsurface, evidenced by the widespread crustal clays, Ehlmann told . This means the majority of the clays on Mars formed underground, and did not require surface water.