Caves carved by water on Mars may hold signs of past life

Caves carved by water that once flowed beneath the surface of Mars could be ideal for… life to flourishif it once existed on the Red Planet and they could preserve traces of it today.

Mars riddled with holes they appear to be cave entrances, but are usually found near regions that are thought to have been volcanically active, suggesting they were formed by processes such as underground lava flows rather than the passage of water.

There are thousands of caves on Earth formed when water dissolves soluble rocks, known as karst caves. But scientists have yet to find signs of such caves on Mars, despite evidence that the planet was covered in water billions of years ago.

Now, Chunyu Ding from Shenzhen University in China and colleagues say they have identified eight possible caves that appear to have been created by ancient water flows rather than volcanic activity. The caves are in the Hebrus Valley, a northwestern region consisting of hundreds of kilometers of valleys and depressions that appear to have been created by ancient floods.

These caves have been mapped by previous Mars missions, such as NASA's Mars Global Surveyor, which orbited Mars from 1997 to 2006. Dean and his team used spectrometry data from this mission to analyze material around the cave entrances. This shows that they contain large amounts of carbonate and sulfate minerals, which usually form in the presence of water.

They also found evidence of ancient streams that end near the cave entrances. This is similar to what we see near karst caves on Earth, says James Baldini at Durham University in the UK. “If you look at a map, you would expect a stream to appear on the surface and then suddenly disappear because the water in the river is captured by the cave system.”

Daniel Le Corre from the University of Kent in the UK say mineralogical and geological evidence suggests they may be water caves, but there is nothing in their appearance that is strikingly different from other caves on Mars. “I spent too much time looking at the global catalog of caves on Mars, and they are indeed very similar to those known to be of volcanic origin,” he says.

If they are water caves, they may be particularly good places to look for life. “For life to exist, you need water and an environment protected from the intense radioactive bombardment on the surface of Mars,” Baldini says. “Volcanic caves and lava tubes are also good places to look for life, but water is not necessarily present.”

Martian water caves may also contain stalagmites, bulbous, protruding rock columns often found in karst caves on Earth, which may act as time capsules for aspects of Mars' ancient environment such as its temperature.

But stalagmites can take many thousands of years of constant flow of water to form, and even if we manage to send a rover or drone into the caves to take samples, determining exactly when the stalagmites formed could be extremely difficult, Baldini says.

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