Martian moon · moon of Mars
Deimos
The smaller, outer moon of Mars: a tiny, smooth-looking body blanketed in fine dust, possibly a captured asteroid or impact debris.
- Distance from Earth today
- 211.9 million km1.416 AU · light: 11 min 47 s
- Distance from the Sun today
- 238.8 million km1.596 AU
- As of
- 3 November 2026position from NASA/JPL orbital elements
Where it is today
Top view of the plane of Earth’s orbit, compressed distance scale. Open on the big map with the time slider →
Facts
- Diameter
- 12.4 km
- Mass
- 0.00144 × 10¹⁸ kg
- Density
- 1,471 kg/m³
- Mean distance from the planet
- 23,457 km
- Orbital period
- 30.3 h
- Orbital eccentricity
- 0.0000
- Orbital inclination
- 1.8°
Source of the figures: JPL SSD – Planetary Satellites (public domain).
Discovery: 1877 – Asaph Hall
Description
Deimos is the smaller and more distant of Mars's two moons, found by Asaph Hall in 1877 a few days before Phobos and named after the Greek personification of dread. It is irregular in shape, but a thick layer of loose dust fills in many of its craters and gives it a smoother look than its sibling. Whether Deimos and Phobos are captured asteroids or debris from a giant impact on Mars is still debated. Viking orbiters made close passes in the 1970s, and in 2025 ESA's Hera spacecraft imaged it during a gravity-assist flyby of Mars.