The outer satellite of Mars, distance 23 460 km from the planet's centre, orbital period 1.262 days. Deimos is irregular in shape, 16 × 12 × 10 km across its three axes. It spins on its shortest axis in the same time that it takes for one orbit, and so keeps the same face towards Mars. Deimos was discovered in 1877 by A. Hall. Its surface is covered with impact craters, but it is smoother than Phobos as many of its craters appear to have been infilled. Deimos may be a captured C-class asteroid.
Subjects: astronomy and cosmology.