Phobos
Phobos
Moon of Mars
Phobos facts
- Orbits
- Mars
- Distance from Mars
- 9,376 km (2.8 Mars-radii)
- Orbital period
- 0.32 days
- Diameter
- 22 km
- Mass
- 1.06 × 10¹⁶ kg
- Orbital inclination
- 1.08°
- Tidally locked
- Yes
- Discovered
- 1877, by Asaph Hall
Phobos orbits Mars
Watch Phobos (highlighted) circle Mars. Press play; the moons run at their real relative speeds.
Relative sizes and spacing are compressed; orbits shown coplanar. Click a moon for its page.
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About Phobos
Phobos is the larger and inner of Mars's two tiny moons, a lumpy, cratered object only about 22 km across. It circles Mars in under eight hours, faster than the planet rotates, so from the surface it rises in the west. Tidal forces are dragging it inward, and it will break up or crash in tens of millions of years.
- Named after the Greek personification of fear, a son of Ares
- Discovered: 1877, by Asaph Hall
Phobos: frequently asked questions
- What is Phobos?
- Phobos is the larger and inner of Mars's two tiny moons, a lumpy, cratered object only about 22 km across.
- What planet does Phobos orbit?
- Phobos orbits Mars at an average distance of about 9,376 km, completing one lap every 0.32 days.
- How big is Phobos?
- Phobos has a diameter of about 22 km and a mass of roughly 1.06 × 10¹⁶ kg.
- Why is Phobos famous?
- Phobos's claim to fame: orbits Mars so low and fast that it laps the planet, rising in the west, and is slowly spiralling inward.
See Phobos in motion
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Data from NASA/JPL and NSSDCA. Source.