Major MoonMoon of Mars
Phobos
The larger and closer of Mars's two moons, slowly spiraling toward the planet.
22.4km
Diameter9,376km
From Mars0.3days
Orbital Period1877
DiscoveredAbout
Phobos is the larger and closer of Mars's two moons. It orbits so close to Mars that it completes an orbit in just 7 hours and 39 minutes, faster than Mars rotates. Phobos is gradually spiraling inward and will either crash into Mars or break apart in about 50 million years.
Properties
22.4km
Diameter9,376km
Semi-major Axis0.32days
Orbital Period1.0659e16kg
Mass1.88g/cm³
DensityYes
Tidally Locked1877
Discovery YearAsaph Hall
Discovered ByNotable Facts
01
Phobos orbits Mars faster than Mars rotates, rising in the west and setting in the east
02
It will either crash into Mars or break apart into a ring in about 50 million years
03
Stickney crater, its largest feature, is nearly half the moon's diameter