The drying out of Mars has been observed by NASA’s Mars Reconnaissance Orbiter, thanks to layers of rock in a crater measuring 155 kilometres across.

Inside the Gale Crater on Mars are exposed layers of rock kilometres thick, dating back billions of years. These rocks are sedimentary, and new data on them collected by the orbiter shows how the red planet dried up, according to a paper in Geophysical Research Letters.

While the lower layers show evidence of clay minerals associated with wet conditions, these become mixed with sulphates as you rise up the rock layers and eventually the sulphates totally dominate the clays. At the uppermost layers there are no water-related minerals at all, report Ralph Milliken, of NASA’s Jet Population Lab in California, and his colleagues.

“These transitions may represent the progressive ‘drying out’ of Mars from early clement conditions, to water-limited acidic and oxidizing conditions, and ultimately to the cold, dry climate of today in a single stratigraphic sequence,” they write in their paper.

The findings support previous explanations of Martian climate reported in Science.

Image: layers in upper formation of Gale Crater Mound / NASA/JPL-Caltech/University of Arizona