The Moons of Mars

Phobos and Deimos

Structure

Phobos and Deimos have only two layers; an interior and a crust. Both interior and crust are made of the same stuff; the crusts, however, are solid and the interiors are not. The crusts are thin.
Phobos and Deimos are potato-shaped, both because they have been bombarded by asteroids and because they are so small.

History

It is believed that Phobos and Deimos are captured asteroids.
In the early 1600s, Kepler predicted that Mars should have two moons. He got that right, but his reasoning was wrong; he figured that because Earth has one moon and Jupiter was thought to have four, Mars should come in the middle of the geometric order with two. Phobos and Deimos weren't discovered until 1877. They were seen as two tiny bright moving dots. Only in late 1971 was any more information gathered about them; for a few days, while a dust storm obscured Mars's features, Mariner 9 studied the size and shape of Phobos and Deimos.

Phobos Facts
	Customary	Metric	Comparison to the Moon
Length	17 mi	27 km	The Moon is 127 Phoboses side to side
Orbital Period	7 hrs 40 minutes		It takes the Moon 85 times as long to circle its planet
Deimos Facts
	Customary	Metric	Comparison to the Moon
Length	9 mi	15 km	The Moon is 240 Deimoses side to side
Distance to Mars: Average	12,000 mi	20,000 km	The Moon is 20 times as far from the Earth as Deimos is from Mars
Orbital Period	About 1 Earth day		It takes the Moon almost 30 times as long to circle its planet

Mars