Just south of the Martian equator, in the Western Hemisphere of that world, a great crater thought to be some 3.8 billion years old stretches 96 miles across the arid surface of the planet. Curiosity, our most advanced robotic explorer on Mars, is currently roving around the Gale crater, taking samples and analyzing the composition of crater material. The trusty bot previously revealed that Gale crater was likely once an enormous lake that stretched for miles “with water that we would even have been able to drink,” said Jens Frydenvang, a rover-team scientist at Los Alamos National Laboratory and the University of Copenhagen, in a press release.
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Now Curiosity has found evidence that Gale crater not only held water in the past, but that the water was retained in the ground for much longer than previously thought, long after the lake itself had evaporated after hundreds of millions of years. Deposits of silica in pale geologic formations called “halos” were found along the crater floor. These silica deposits likely came from deeper deposits of rock and were carried to the surface by seeping flows of groundwater. A new study on the findings was recently published in Geophysical Research Letters.
“The concentration of silica is very high at the centerlines of these halos,” said Frydenvang. “What we’re seeing is that silica appears to have migrated between very old sedimentary bedrock and into younger overlying rocks.” That migration took place when the silica dissolved in water and then seeped to the surface, where the water evaporated and the silica halos were deposited.
These halo samples were analyzed by Curiosity’s science instruments, including the ChemCam, which shoots a laser into mineral samples to analyze the spectrum and determine the composition. This revealed that surprisingly high concentrations of silica are deposited on the crater floor of Gale.
“What this finding tells us is that, even when the lake eventually evaporated, substantial amounts of groundwater were present for much longer than we previously thought—thus further expanding the window for when life might have existed on Mars,” said Frydenvang. “Silica found in halos in younger rocks close by was likely remobilized from the old sedimentary rocks by water flowing through the fractures.”
Frydenvang told Popular Mechanics in an email that it can be incredibly difficult to set hard dates for when these processes took place without access to samples of Martian material in labs on Earth for chemical analysis. However, these silica halos likely formed more than two billion years ago, meaning the ground in this area could have been saturated with water for billions of years after the lake itself evaporated.
Whether microbes could have thrived in this wet environment is yet to be known, but as the upcoming Mars 2020 rover will collect samples and deposit them to be picked up and returned to Earth by another mission, we are on our way to gathering some of this precious Martian soil to analyze on Earth. In the coming years, we could finally crack the code and answer the question: did Mars ever host life? And even, is there possibly life there still?