Salt-bearing sediments within the Gale crater on Mars, detected by NASA’s rover Curiosity, suggest that salty lakes were once present at this location. The findings, presented in Nature Geoscience this week, echo previous inferences from satellite observations that the red planet underwent a transition to arid climates in this time frame, around 3.5 billion years ago.

A diverse range of salts have been detected in situ on Mars and interpreted as indicators of ancient brines - saline waters that became more abundant as the Martian climate experienced arid cycles. One goal of Curiosity’s mission exploring Gale crater is to better understand how liquid water disappeared from Mars’s surface.

William Rapin and colleagues report the detection of sulfate salts disseminated in sedimentary rocks, dating to around 3.3 - 3.7 billion years ago (the Hesperian time period). These salts were not found in such form and abundance in older rocks previously analysed by Curiosity. Thus, the researchers infer that the measurements are evidence of an interval of high salinity of the crater's lake that may have occurred as water evaporated. These findings support hypothesized fluctuations of the Martian climate during the Hesperian period.

Future exploration of younger rocks in Gale crater by Curiosity is expected to reveal additional insights on the drying out of Mars’s surface.