NASA’s Curiosity rover continues exploring the red planet and its Gale Crater making incredible discoveries along the way.
Traces of ancient shallow brine ponds that overflowed and dried have been identified by the Curiosity rover on rocks rich in mineral salts at the Gale Crater.
This discovery tells a lot about ancient Mars.
Go back a few billion years and imagine ponds dotting the floor of the Gale Crater. Streams most likely laced the walls of the crater, running towards its base. Fast forward a few million years, and you’d probably see how this waterway overflow and then dry up, signalizing a cycle that was most likely repeated countless times over millions of years as Mars changed in ways we are only now discovering.
These salt deposits – described by scientists in a study published in Nature Geoscience – serve as a kind of watermark created by climatic fluctuations as the Martian environment went from being wetter to the icy desert it is today.
Scientists would like to understand how long this transition went on, and when exactly it happened.
This last clue may be a sign of the findings that will come as Curiosity moves towards a region called “sulfate-bearing unit,” which is expected to have formed in an even drier environment.
It represents a big difference from the lower part of Mount Sharp in the center of the Gale crater, where Curiosity discovered evidence of persistent freshwater lakes.
As explained by NASA, the Gale Crater is the ancient remnant of an extensive impact. Sediment carried by water and wind ultimately filled in the crater floor, layer by layer. After the sediment hardened, the wind then carved the layered rock into the towering Mount Sharp we see today, which Curiosity is currently climbing as you are reading this.
Now exposed on the mountain’s slopes, each layer exposes a distinct era of Martian history and holds clues about the prevailing conditions 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?”
Rapin and his colleagues report salts located across a 500-foot-tall (150-meter-tall) section of sedimentary rocks called “Sutton Island,” which Curiosity explored back in 2017. Based on a series of mud cracks at a place named “Old Soaker,” the team already knew the area had irregular drier periods. But the Sutton Island salts implies the water also concentrated into brine.
Usually, when a lake dries up entirely, it leaves loads of pure salt crystals behind. But the Sutton Island salts are distinct: For one thing, they’re mineral salts, and not table salt. They’re also mixed with sediment, implying they crystallized in a wet environment — possibly just underneath evaporating shallow ponds filled with briny water.
Since scientists think that Earth and Mars were similar in their early days, Rapin and his team speculated that Sutton Island might once have resembled a type of saline lake on South America’s Altiplano. Streams and rivers flowing from mountain range into an arid, high-altitude plateau lead to closed basins similar to those found on Mars’ ancient Gale Crater. Lakes on the Altiplano are heavily influenced by the climate in the same way as Gale, NASA has revealed.
“During drier periods, the Altiplano lakes become shallower, and some can dry out completely,” Rapin said. “The fact that they’re vegetation-free even makes them look a little like Mars.”