China's Mars Rover Discovers Signs of Recent Water in Martian Sand Dunes

The Associated Press reports that "water may be more widespread and recent on Mars than previously thought, based on observations of Martian sand dunes by China's rover." A paper published in Science suggests thin films of water appeared on sand dunes sometime between 1.4 million years ago and as recently as 400,000 years ago - or perhaps even sooner:The finding highlights new, potentially fertile areas in the warmer regions of Mars where conditions might be suitable for life to exist, though more study is needed... Before the Zhurong rover fell silent, it observed salt-rich dunes with cracks and crusts, which researchers said likely were mixed with melting morning frost or snow as recently as a few hundred thousand years ago... Conditions during that period were similar to now on Mars, with rivers and lakes dried up and no longer flowing as they did billions of years earlier... The rover did not directly detect any water in the form of frost or ice. But Qin said computer simulations and observations by other spacecraft at Mars indicate that even nowadays at certain times of year, conditions could be suitable for water to appear... Small pockets of water from thawing frost or snow, mixed with salt, likely resulted in the small cracks, hard crusty surfaces, loose particles and other dune features like depressions and ridges, the Chinese scientists said. Space.com explains exactly how the discovery was confirmed:The laser-induced breakdown spectrometer (MarSCoDe) instrument onboard the rover zapped sand grains into millimeter-sized particles. Their chemical makeup revealed hydrated minerals like sulfates, silica, iron oxide and chlorides... Researchers say water vapor traveled from Martian poles to lower latitudes like Zhurong's spot a few million years ago, when the planet's polar ice caps released high amounts of water vapor, thanks to a different tilt that had Mars' poles pointed more directly toward the sun. Frigid temperatures on the wobbling planet condensed the drifting vapor and dropped it as snow far from the poles, according to the latest study. Mars' tilt changes over a 124,000-year cycle, so "this offers a replenishing mechanism for vapor in the atmosphere to form frost or snow at low latitudes where the Zhurong rover has landed," Qin told Space.com. But "no water ice was detected by any instrument on the Zhurong rover." Instead, in the same way that salting roads on Earth melts icy patches during storms, salts in Martian sand dunes warmed the fallen snow and thawed it enough to form saltwater. The process also formed minerals such as silica and ferric oxides, which Zhurong spotted, researchers say. The saltwater, however, didn't stay around for long. Temperatures on Mars swing wildly and spike in the mornings between 5 a.m. and 6 a.m., so the saltwater evaporated and left behind salt and other newly formed minerals that later seeped between the dune's sand grains, cementing them to form a crust, according to the study... "The phenomenon was documented at one site, but it should be applicable to a fairly large fraction of Mars' surface at similar latitudes," Manasvi Lingam, an assistant professor of astrobiology at the Florida Institute of Technology who wasn't involved in the new research, told Space.com. Since the rover found water activity on (and in) salty Martian dunes, the researchers now suggest future missions search for salt-tolerant microbes, and are raising the possibility of "extant life on Mars."

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