NASA’s Curiosity Rover Finds Unexplained Oxygen on Mars

NASA’s Curiosity rover, for three Martian years—nearly six years to us Earthlings—has been sniffing the air above Mars’ Gale Crater, its near-equatorial exploration site. Using its Sample Analysis at Mars (SAM) portable chemistry lab, the rover has ascertained not only what the surface-atmosphere is made of, but also how its gases change with the seasons.

Many of Mars’ gases “are very well behaved,” says Melissa Trainer, a planetary scientist at NASA and a team member on the SAM experiment. One, however, appears to be behaving in a decidedly unexpected and altogether bizarre manner: oxygen.

Scientists have long known that carbon dioxide on Mars, which makes up 95 percent of the planet’s atmosphere freezes out over the poles in winter and sublimates back into gas in summer. In the thin air around Gale Crater, Curiosity’s measurements have shown tiny amounts of inert argon and nitrogen periodically rising and falling as expected, due to this seasonal cycling of carbon dioxide

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