Mars once had a thick atmosphere and surface water. But billions of years ago, as the Red Planet's magnetic field dwindled, it began shedding its atmosphere, spewing charged particles into space. Although only wisps remain, it might still be possible to study that ancient atmosphere, according to a paper by researchers at the University of California at Berkeley. The authors say to study the Martian moon Phobos. Because the moon is tidally locked to the Red Planet, the surface constantly facing Mars has been bathed for millennia by the atoms and molecules Mars has been sloughing. A geological sample from Phobos would provide researchers with an archive of the past atmosphere of Mars, embedded in the upper layers of its soil.
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