Deimos is the smaller and outer moon of Mars, a dark, lumpy little body whose surface is smoothed by a blanket of fine dust that fills its craters.
At a glance
| radius | 6.2 km (0.000973 × Earth) |
|---|---|
| distance from its planet | 23,500 km |
| one orbit | 1.26 days |
| geometric albedo | 0.07 |
Read off the piece’s own catalogue, the same values it draws with.
About Deimos
Deimos is a tiny, irregular moon, dark like Phobos and far too small to have pulled itself round. Its surface looks smoother than Phobos’s, because a layer of loose dust has filled in most of its craters. Asaph Hall discovered it along with Phobos, and the two are named after the sons of Ares, the Greek god of war, fear and dread.
It orbits farther out than Phobos, just beyond the distance at which a moon would keep pace with the planet’s turning, so seen from Mars it drifts slowly across the sky and stays up for days at a time. Tides push it very gradually outwards, the opposite of the fate of its inner sibling.
What you see in the piece
Deimos is so small and faint that it shows only when you are close to Mars, a dim speck circling over the planet’s equator well outside the orbit of Phobos.
Measured or modelled
Whether Deimos and Phobos are captured asteroids or formed from debris thrown up by a giant impact on Mars is still debated.
Questions
How big is Deimos?
Its radius is only about 6.2 km (0.000973 × Earth): it is one of the smallest known moons in the Solar System.
How long does Deimos take to orbit Mars?
Deimos completes an orbit every 1.26 days, a little longer than a Martian day, so it creeps slowly across the Martian sky.