Subsurface caves shaped by flowing water on Mars may have provided ideal conditions for life, with potential remnants still present today.

Throughout Mars, numerous openings resembling cave entrances are found, primarily near volcanic regions. This implies these features were likely formed by processes related to volcanic activity rather than water.

Earth is home to numerous karst caves, created by the dissolution of soluble rock by water. However, scientists have yet to find equivalent caves on Mars, despite evidence indicating the planet was once covered in water billions of years ago.

Currently, Ding Vermicelli, a professor at Shenzhen University in China, has identified eight caves that seem to have been formed by ancient water flows instead of volcanic activity. These caves are situated in the Hebrus Gorge, a northwestern region characterized by extensive valleys and depressions likely shaped by ancient floods.

Previous Mars missions, including NASA’s Mars Global Surveyor (which orbited Mars from 1997 to 2006), have mapped these caves. Ding and his team analyzed material near one cave entrance using spectroscopic data from that mission, revealing a notable presence of carbonate and sulfate minerals typically associated with water.

They also detected signs of an ancient stream ending near the cave entrance, similar to patterns seen near karst caves on Earth. James Baldini from Durham University, UK, noted, “On a map, you’d expect a river to emerge to the surface only to disappear suddenly, as the cave system absorbs its water.”

Daniel Le Corret from the University of Kent in the UK mentioned that while the mineralogical and geological data implies these may be water caves, they appear quite similar to other Martian caves of volcanic origin. “I’ve spent countless hours evaluating the global catalog of Martian caves and these resemble known volcanic formations,” he said.

If these caves are indeed formed by water, they might be excellent locations for searching for life. “For life to exist, water and a protective environment from Mars’ intense surface radiation are essential,” Baldini remarked. “Volcanic caves and lava tubes also present good avenues for potential life, though they don’t necessarily involve water.”

Mars’ water caves may contain stalagmites—bulbous rock formations generally found in Earth’s karst caves—and could act as time capsules of Mars’ ancient climate conditions, such as temperature.

However, stalagmites require thousands of years of sustained water flow to develop, and determining their formation timing could be challenging, even if rovers or drones succeed in collecting samples, according to Baldini.

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