Moon of Mars · Updated October 2026
Deimos.
Deimos is the smaller and outer of Mars's two moons, about 12 km across on average and 15 km at its longest. It orbits Mars at 23,458 km once every 30 hours and 18 minutes, only a little longer than a Martian day, so it crosses the Martian sky slowly. Its surface is unusually smooth for such a small body, with small craters partially filled in by regolith.
View Mars system in 3D →Key facts
Deimos is so small that from the Martian surface it would look like a brilliant star, not a disc.
About Deimos
Like Phobos, Deimos has a dark surface similar to the carbon-rich C-type asteroids of the outer asteroid belt, so it may be a captured asteroid; it may instead have formed from debris of a giant impact on Mars, and the question is still open. Both moons are tidally locked, keeping one face toward Mars.
How to view Deimos in 3D
Deimos 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 →More about Mars
Sources & methodology
Numbers cross-referenced with the sources below; updated October 2026.