Moon of Mars · Updated May 2026
Phobos.
Phobos is the larger and inner of Mars's two moons. Just 22 km across, it orbits at only 9,376 km — closer to its planet than any other moon in the solar system — and circles Mars in 7h 39m, faster than Mars rotates. Phobos is spiralling inward by about 1.8 cm per year and will either be torn apart by tidal forces or impact Mars within 30–50 million years.
View Mars system in 3D →Key facts
Phobos orbits so quickly that a Martian observer would see it rise in the west and set in the east twice every Martian day. The viewer reproduces this — set time speed to 50× and watch Phobos flick around Mars while Deimos crawls.
About Phobos
Likely a captured asteroid — its low density and Mars-aligned spectrum suggest a porous, rubble-pile interior. Phobos features the giant Stickney crater, 9 km across — almost half the moon's diameter, hinting at how close the impact came to shattering it. Japan's Martian Moons eXploration (MMX) mission, scheduled for the late 2020s, plans to land on Phobos and return a sample to Earth.
How to view Phobos in 3D
Phobos orbits Mars in real time inside the interactive viewer. Open the parent body to see the orbital geometry, or use the object browser to fly directly to the moon and observe its rotation, surface, and orbit.
Open the Mars system →Sources & methodology
Numbers cross-referenced with the sources below; updated May 2026.