July 21, 2017
Billions of years of cosmic evolution — the birth and death of stars, the slow coalescence of planets, the patient unfolding of life — all...
Phobos: Moon over Mars
Birthday · July 21, 2017
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APOD published July 21, 2017. Full image credits are on the original APOD entry below. A publication-date match, not a photo taken on your date. Independent of NASA.
A tiny moon with a scary name, Phobos emerges from behind the Red Planet in this timelapse sequence from the Earth-orbiting Hubble Space Telescope. Over 22 minutes the 13 separate exposures were captured near the 2016 closest approach of Mars to planet Earth. Martians have to look to the west to watch Phobos rise, though. The small moon is closer to its parent planet than any other moon in the Solar System, about 3,700 miles (6,000 kilometers) above the Martian surface. It completes one orbit in just 7 hours and 39 minutes. That's faster than a Mars rotation, which corresponds to about 24 hours and 40 minutes. As a result, seen from the surface of Mars speeding Phobos rises above the western horizon 2 times in a Martian day. Still, Phobos is doomed.