Phobos

One of the two moons of Mars, discovered in 1877 by the US astronomer Asaph Hall. It is an irregularly shaped lump of rock, cratered by meteorite impacts. Phobos is 27 × 22 × 19 km/17 × 13 × 12 mi in size, and orbits Mars every 0.32 days at a distance of 9,400 km/5,840 mi from the planet's centre. It is thought to be an asteroid captured by Mars's gravity.

Phobos is named after a son of Ares and Aphrodite from Greek mythology. Phobos has been photographed by three separate probes - Mariner 9 in 1971, Viking 1 in 1977, and Phobos in 1988. A Russian probe called Phobos-Grunt is scheduled to be launched toward Phobos in 2009. (‘Grunt’ means ‘ground’ - the probe will return a Phobos soil sample.)