Water on Mars evaporated a billion years later than thought: NASA

Observations with NASA’s MRO (Mars Reconnaissance Orbiter) mission have made it possible to determine that the superficial water left salt minerals on Mars 2 billion years ago.

Mars once filled with rivers and ponds billions of years ago, providing a potential habitat for the microbial life. As the planet’s atmosphere thinned over time, that water evaporated, leaving the frozen desert world that MRO studies today.

It is commonly believed that the water on Mars evaporated about 3 billion years ago. But two scientists studying the data that MRO has accumulated on Mars over the past 15 years have found evidence that significantly shortens that timeline: Their research reveals signs of liquid water on the Red Planet as recently as 2,000 to 2,500 years ago. million years, meaning the water flowed there about a billion years longer than previous estimates.

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The findings, published in “AGU Advances” on December 27, 2021, focus on the chloride salt deposits left behind when the frozen water flowing across the landscape evaporated.

While the shape of certain valley networks hinted that water may have flowed on Mars recently, salt deposits provide the first mineral evidence confirming the presence of liquid water.

The discovery raises new questions about how long microbial life might have survived on Mars, if it ever formed. In the LandAt least where there is water, there is life.

The study’s lead author, Ellen Leask, did much of the research as part of her doctoral work at Caltech. She and Caltech professor Bethany Ehlmann used data from the MRO instrument called the Compact Reconnaissance Imaging Spectrometer for Mars (CRISM) to map chloride salts in the clay-rich highlands of Mars’ southern hemisphere, a terrain pockmarked by craters of impact.

These craters were a key to dating the salts: the fewer craters a terrain has, the younger it is. By counting the number of craters in a surface area, scientists can estimate their age.

MRO has two cameras that are perfect for this purpose. The context camera, with its wide-angle black-and-white lens, helps scientists map the extent of chlorides. To zoom in, scientists turn to the High Resolution Imaging Science Experiment (HiRISE) color camera, which allows them to see details as small as a Mars rover from space.

Using both cameras to create digital elevation maps, Leask and Ehlmann found that many of the salts were in depressions, which once held shallow pools, on gently sloping volcanic plains.

Scientists also found winding, dry channels nearby, ancient streams that once fed surface runoff (from occasional ice melt or permafrost) into these ponds. Crater counting and evidence of salts on top of the volcanic terrain allowed them to date the deposits.

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“What’s amazing is that after more than a decade of providing high-resolution, stereo, and infrared images, MRO has fueled new discoveries about the nature and timing of these ancient river-connected salt ponds,” Ehlmann said in a statement. deputy research director of CRISM.

His co-author, Leask, is now a postdoctoral researcher at the Johns Hopkins University Applied Physics Laboratory, which leads CRISM.

Salt minerals were first discovered 14 years ago by NASA’s Mars Odyssey orbiter, which launched in 2001. MRO, which has higher-resolution instruments than Odyssey, launched in 2005 and has been studying salts, among many other features of Mars, since then.

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