Imagine ponds dotting the floor of Gale Crater, the 100-mile-wide (150-kilometer-wide) ancient basin that Curiosity is exploring.
Streams might have laced the crater’s walls, running toward its base. Watch history in fast forward, and you’d see these waterways overflow then dry up, a cycle that probably repeated itself numerous times over millions of years.
That is the landscape described by Curiosity scientists in a Nature Geoscience paper published today.
The authors interpret rocks enriched in mineral salts discovered by the rover as evidence of shallow briny ponds that went through episodes of overflow and drying.
The deposits serve as a watermark created by climate fluctuations as the Martian environment transitioned from a wetter one to the freezing desert it is today.
Scientists would like to understand how long this transition took and when exactly it occurred. This latest clue may be a sign of findings to come as Curiosity heads toward a region called the “sulfate-bearing unit,” which is expected to have formed in an even drier environment. It represents a stark difference from lower down the mountain, where Curiosity discovered evidence of persistent freshwater lakes.
The Curiosity rover has taught us a lot about the history of Mars and its potential to support life. Take a tour of its landing site, Gale Crater. Watch the video below
Gale Crater is the ancient remnant of a massive impact. Sediment carried by water and wind eventually filled in the crater floor, layer by layer.
After the sediment hardened, wind carved the layered rock into the towering Mount Sharp, which Curiosity is climbing today.
Now exposed on the mountain’s slopes, each layer reveals a different era of Martian history and holds clues about the prevailing environment at the time.
“We went to Gale Crater because it preserves this unique record of a changing Mars,”
said lead author William Rapin of Caltech.
“Understanding when and how the planet’s climate started evolving is a piece of another puzzle: When and how long was Mars capable of supporting microbial life at the surface?”
He and his co-authors describe salts found across a 500-foot-tall (150-meter-tall) section of sedimentary rocks called “Sutton Island,” which Curiosity visited in 2017. Based on a series of mud cracks at a location named “Old Soaker,” the team already knew the area had intermittent drier periods. But the Sutton Island salts suggest the water also concentrated into brine.