Phobos, the larger moon of Mars, has already taken a pounding. A collision with another large space rock gouged the crater at right, and created cracks through the moon that are evident on the surface. But Phobos' fate is even more violent. The moon is spiraling closer to Mars, and eventually the planet's gravity will pulverize it. This image, from Mars Reconnaissance Orbiter, was enhanced to bring out subtle variations in color on Phobos' surface. [NASA/LPL/MRO]
Phobos, the larger moon of Mars, could be one of the solar system’s most exciting thrill rides. But if you’re not careful, it could become a little too thrilling — one big push and you’d float off into space.
Phobos is a lumpy boulder that’s only about 15 miles in diameter. Its main feature is a giant impact crater. The impact that gouged it was so strong that it almost blasted the moon to bits.
Phobos orbits just 3700 miles above the Martian surface. At that altitude, it moves so quickly across the Martian sky that it rises in the west and sets in the east, with moonrises about 11 hours apart.
Seen from Phobos, Mars would span about a quarter of the sky, and its surface would slide past you at about a thousand miles per hour. So in a single circle around Mars — daylight permitting — you’d see everything from the giant volcanoes of the Tharsis Ridge to Valles Marineris, a complex of canyons that dwarfs the Grand Canyon here on Earth. But because of Phobos’s low altitude, you wouldn’t see Mars’s polar ice caps — they’d be hidden around the curve of the planet itself.
You wouldn’t want to get too excited by the view, though. The gravity of Phobos is so weak that a single big jump would launch you into space — leaving the Martian moon behind.
Mars is in our own sky right now, quite low in the west-southwest as twilight begins to fade. It looks like an orange star. And this evening, it’s well below the crescent Moon.
Script by Damond Benningfield, Copyright 2012
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