Deimos [DEE-mos] is the outermost moon of Mars and is the smaller of the two. With a length of only 9.9 miles (11 km), It is also one of the smallest known moons in the Solar System. Deimos was named after Terror, another of the charioteers of the Roman god, Mars. In Greek mythology, Deimos is one of the sons of Ares (Mars) and Aphrodite (Venus). Deimos was discovered in 1877 by American astronomer Asaph Hall while observing Mars at the U.S. Naval Observatory.
The Smallest Moon
If we thought Phobos was a small moon, Deimos is even smaller. At 9.9 miles (11 km) in length, it is little more than a pockmarked chunk of rock in orbit around the red planet. At a distance of 14,573 miles (23,460 km), Deimos is more than twice as far from Mars than Phobos. It appears a little more than a moderately bright spot in the Martian sky. Like Phobos, its irregular shape bears more of a resemblance to the large asteroids in the asteroid belt between Mars and Jupiter. It is possible that is was an asteroid at one time, but was captured by the gravity of Mars. Some astronomers believe this not to be true. We will probably never know for sure.
Features of Deimos
Line Phobos, Deimos is a rather unremarkable object. It, too, is essentially just a large rock potted with several craters. Deimos does have a much smoother appearance and fewer craters than its cousin, Phobos. The largest of these craters is two miles in diameter, about 1/5 the size of the moon itself. Unlike Phobos, Deimos shows no evidence of surface fracturing. This may be because it is twice as far from Mars as Phobos, and not subject to the same strong gravitational forces. Like Phobos, Deimos is believed to be composed of a mixture of ice and carbon-rich rock like that found in the C-type asteroids in the outer asteroid belt. Deimos has no atmosphere and no magnetic field.
