NASA | Mapping Mars' Upper Atmosphere

High above the thin Martian skies, NASA’s MAVEN spacecraft is carrying out a mission: determine how Mars lost its early atmosphere, and with it, its water. While previous Mars orbiters have peered down at the planet’s surface, MAVEN is spending part of its time gazing at the stars, looking for subtle changes in their color as they dip through the limb of Mars and set below the horizon. Such stellar occultations reveal what Mars’ atmosphere is made of, and how its composition varies with altitude. MAVEN’s observations are providing scientists with the most detailed picture of the Mars upper atmosphere to date, helping them understand how a once-hospitable world changed into the forbidding desert that we see today.

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