Ancient Martian volcanoes shed light on ice sheets

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A graphic showing where minerals indicate where a volcano erupted beneath an ice sheet. The site is far from any ice sheet on modern Mars. – NASA/JPL-Caltech/JHUAPL/ASU

Ice sheets once covered much more of the surface of Mars than they do today, which, combined with volcanic activity, could have set the stage for microbial life to thrive, new evidence from NASA's Mars Reconnaissance Orbiter suggests.

The orbiter's mineral-mapping spectrometer collected surface composition data in a region of southern Mars called "Sisyphi Montes", noted for the many flat-topped mountains resembling extinct volcanoes on Earth. The region is also far away from current ice sheets on the Red Planet.

"Rocks tell stories. Studying the rocks can show how the volcano formed or how it was changed over time," Sheridan Ackiss of Purdue University, Indiana, said. "I wanted to learn what story the rocks on these volcanoes were telling."

The orbiter found mineral deposits very similar to those found on Earth when a volcano erupts beneath a sheet of ice on Earth. Such eruptions rapidly generate steam that leads to explosions that punch through the ice, propelling ash high into the sky. 

The orbiter's spectrometer discovered minerals including zeolites, sulfates and clays the same as would be seen on Erath following a sub-glacial eruption.

The Sisyphi Montes region extends from about 55 degrees to 75 degrees south latitude. Some of the sites that have shapes and compositions consistent with volcanic eruptions beneath an ice sheet are about 1,600 kilometres from the current south polar ice cap of Mars. The cap now has a diameter of about 350 kilometres.

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