The abnormal moons of Mars

In 1988 the soviet Union launched two probes to study Mars and its two moons Phobos and Deimos. Unlike most other Russian missions around the solar system, the Phobos I and II missions were done with some cooperation with the United States, which contributed the use of the Deep Space radio telescope network, along with various contributions from Sweden, Switzerland, Austria, Germany and France. The missions were to provide the first close look at Phobos and Deimos, and hopefully answer the question as to why these two moons are unlike anything else in the solar system.   The names of the two moons comes from greek mythology, after the sons of the god Mars. Phobos (meaning fear) and Deimos (meaning panic) both appear, at least according to current science, to be ex-asteroids that were captured by Mars' gravity, rather than being moons in the traditional sense. They are both quite small, being only a few tens of kilometers in size, and are tootiny for their gravity to pull themselves into spheres as with most larger moons in the solar system, and as a result they resemble an oblong potato.   Deimos is the smaller of the two, and orbits mars more distantly than Phobos. We know it has a composition similar to a meteorite sometimes found on earth called a carbonaceous chondrite, a fascinating group of rocks that contain not only the most ancient material known to man, some of which predates the solar system entirely, but also amino acids which are organic molecules that form the basis for life. Oddly, Deimos is relatively uncratered.

In contrast, Phobos is heavily cratered, and orbits Mars in a very bizarre way; it moves so fast that it rises and sets to an observer on Mars twice each day, and due to that speed appears to rise in the west and set in the east, the opposite of earth's own moon. Phobos seems to be composed of the same materials as Deimos, but for some reason, the moon has a seriously low density. So low that in the 1960's Russian planetary scientists suggested that the moon was hollow, and might be an artificial satellite.