Phobos is the larger and closer of Mars' two moons (the other being Deimos), both discovered by Asaph Hall. It is named after the Greek godPhobos (which means "fear"), a son of Ares (Mars). Its surface is mostly composed of carbonaceous chondrites and is heavily cratered. Phobos is one of the smallest moons in the solar system, and orbits about 9377 km (5823 mi) above the surface of Mars, closer to its primary than any other planetary moon. Because of this close orbit, the moon will crash into Mars' surface in the future. Phobos can cast shadows onto the surface of Mars when it passes between the Sun and Mars. Phobos' origin is unclear, and has been identified as a captured asteroid or even the remains of a planetesimal. One debunked claim suggested that Phobos is of artificial origin and is hollow. Spacecraft have imaged Phobos while orbiting Mars. The Phobos spacecraft were meant to explore Phobos in greater detail, but both failed en route. There are future plans to explore this moon.
Percival Lawrence Lowell (March 13, 1855 – November 12, 1916) was a businessman, author, mathematician, and astronomer who fueled speculation that there were canals on Mars, founded the Lowell Observatory in Flagstaff, Arizona, and formed the beginning of the effort that led to the discovery of Pluto 14 years after his death. The choice of the name Pluto and its symbol were partly influenced by his initials PL.