NASA's Curiosity rover, a space exploration vehicle created to move across the surface of Mars, has detected sulfate salt sediments in Gale Crater, a dry lake bed on the planet, suggesting that the crater once contained salty lakes which could have supported life. Now, Curiosity has found sediments containing sulfate salt in the crater, which suggest it once held salty lakes.
A range of salts have been found on Mars in different locations.
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. Salty water formations seemed to increase on the Martian surface as the planet transitioned to an arid climate 3.5 bullion years ago. This tells researchers that the lake-bed rocks must have dried out nearly completely at times, pointing to fluctuations in the Martian climate.
Mars is now in the middle of an ice age, and before this study, scientists believed liquid water could not exist on its surface.
Gale Crater is the ancient remnant of a massive impact. Those same layers act like chapters in the history of Mars and provide clues to its environment at each point in time.
The findings were published Monday in the journal Nature Geoscience.
"We went to Gale Crater because it preserves this unique record of a changing Mars", said William Rapin of Caltech.
Scientists believe that the sulfates were left over after ancient brines, which may have once contained life forms, evaporated during the Hesperian Period on Mars, in which extensive volcanic activity and catastrophic flooding took place, eventually leaving the planet with a much more arid climate. It represents a stark difference from lower down the mountain, where Curiosity discovered evidence of persistent freshwater lakes.
Curiosity can study the composition of salts on the planet's surface using a setup called ChemCam, which uses a laser to vaporise rocks and a camera to spectrographically analyse the composition of the resulting gases.
Given that Earth and Mars were similar in their early days, NASA speculated that Sutton Island might have resembled saline lakes on South America's Altiplano.
Lakes on the Altiplano are heavily influenced by climate in the same way as Gale. "The fact that they're vegetation-free even makes them look a little like Mars".
NASA's Curiosity rover has been exploring the Gale crater since August 2012. After the sediment hardened, wind carved the layered rock into the towering Mount Sharp, which Curiosity is climbing today. Now, it's exploring larger rocks that could have formed due to wind and water forces. "What these new findings show is that the climate on Mars was not as stable as we thought it was".