For decades, planetary geologists have speculated that glaciers might once have crept through Valles Marineris, the 3,218-kilometre-long chasm that constitutes the Grand Canyon of Mars.
Using satellite images, researchers have identified features that might have been carved by past glaciers as they flowed through the canyons; however, these observations have remained highly controversial and contested.
Now, a joint team from Bryn Mawr College in the US and the Freie Universitaet Berlin has identified what could be the first mineralogical evidence of past glaciers within the Valles Marineris: a layer of mixed sulphate minerals halfway up the 4.8km high cliffs of Ius Chasma at the western end of the canyon system.
The team - including Selby Cull, Patrick McGuire and Christoph Gross, and Bryn Mawr undergraduate student researchers Jenna Myers and Nina Shmorhun - mapped the acid-sulfate mineral jarosite along the canyon wall.
They speculate that it may have formed via a mechanism similar to one observed at glaciers in the Svalbard, a Norwegian archipelago in the Arctic Ocean, on Earth.
"Atmospheric sulphur becomes trapped in the ice, is warmed by the sun, and reacts with the water to produce highly acidic sulfate minerals like jarosite along the margins of the glacier," researchers said.
The study was published in the journal of Geological Society of America.