How long does Phobos, Mars’s larger moon, take to orbit the planet?

Phobos takes about 7 hours 39 minutes to orbit Mars.

Phobos is the larger and closer of Mars’s two moons. Its orbit is so close to the planet that it circles Mars faster than Mars rotates. As a result, an observer on the Martian surface would see Phobos rise in the west and set in the east roughly twice during a Martian day.

The moon’s orbit is gradually shrinking because of tidal interactions with Mars. Over tens of millions of years, Phobos is expected either to break apart and form a debris ring or crash into the planet.

Phobos is often confused with Deimos, the smaller and more distant moon. Deimos takes about 30 hours to orbit Mars, whereas Phobos completes an orbit in less than eight hours.