Moon and Mars

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 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 it would slide past at about 5,000 miles per hour. So in a single orbit around Mars — daylight permitting — you’d see everything from the giant volcanoes of Tharsis Ridge to Valles Marineris, a complex of canyons that dwarf the Grand Canyon here on Earth. But because of Phobos’s low altitude, you wouldn’t see the Red Planet’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, well up in the west-southwest at nightfall. It looks like a bright orange star. Tonight, it’s well below the first-quarter Moon, and leads the Moon down the western sky.
 

Script by Damond Benningfield