Martian atmospheric oxygen, carbon, nitrogen and argon ions have been escaping Mars for billions of years and could be preserved inside the uppermost hundreds of nanometers of Phobos’ nearside regolith grains, which may be brought back to Earth by future sample return missions. The High Resolution Imaging Science Experiment (HiRISE) camera on NASA’s Mars Reconnaissance Orbiter captured this image of the larger of Mars’ two moons, Phobos, on...
