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Conditions on Mars make it pretty inhospitable to life. Temperatures can dip below minus 100 degrees Fahrenheit, high-energy UV radiation buffets the planet, and “dust devils” can strafe the surface with 99 mile per hour winds. So if creatures of some sort live on the Red Planet, or have ever lived there, they’d be better off sheltering in caves.
Now, scientists in China and Italy say they may have discovered a new category of Martian cave formed by liquid water dissolving rock. The majority of caves found on Mars were formed by volcanic or tectonic processes. But these potential new features, called karstic caves, have different origin stories. And because their formation may have involved water in its liquid form, they could serve as targets to look for traces of life.
Karstic caves also exist on Earth, where slightly acidic groundwater breaks down soluble rocks such as gypsum or limestone. This forges fractures that can expand until they become caves. On Mars, ancient water flows might have dissolved sulfate- and carbonate-rich rocks on the planet’s crust to form the newly discovered caves.
Researchers spotted holes called skylights that might lead to karstic caves on Mars in the planet’s Hebrus Valles region. This area contains scars from ancient floods—a phenomenon thought to have transpired throughout the Red Planet—such as troughs and channels. NASA spacecraft, including Mars Global Surveyor and Mars Odyssey, have collected detailed scans and imagery in this intriguing region.
Read More: “The Race to Colonize Mars Perpetuates a Dangerous Religion”
With this information, scientists took a closer look at eight pits in Hebrus Valles. They found that, unlike impact craters, these are deep and mostly circular depressions. They also noticed that the rocks surrounding these pits have plenty of carbonates and sulfates, minerals that are highly dissolvable. They published their findings recently in The Astrophysical Journal Letters.
“These skylights represent promising subsurface refugia,” the authors wrote, suggesting that future robotic and human missions visits could encounter hints of past water activity and even preserved signs of life. Plus, a statement notes, they could give astronauts a place to rest their heads and get out of the harsh Martian weather. 
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Lead image: ESA & MPS for OSIRIS Team MPS/UPD/LAM/IAA/RSSD/INTA/UPM/DASP/IDA
