Huge glaciers may once have crept through Mars' version of the Grand Canyon. That's according to new analysis of data from NASA's Mars Reconnaissance Orbiter (MRO) spacecraft, which has spotted telltale signs of minerals left in the glaciers' wake.

Rock formations around Valles Marineris, a system of canyons running more than 4000 kilometres across the Red Planet's equator, have hinted that it once held glaciers that melted and caused a megaflood. Now Selby Cull at Bryn Mawr College in Pennsylvania and colleagues have found mineralogical evidence that supports the idea.

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