The planet Mars has two extremely small natural moons or satellites. Their names are Phobos and Deimos. They were the sons of Mars in Greek mythology. Their names mean fear and terror. Mars was the god of war.
Phobos and Deimos were discovered in August, 1877 by the American Astronomer Asaph Hall. At the time of their discovery, it was estimated that both moons were nearly spherical in shape.
The inner moon, Phobos, was thought to be approximately ten miles in diameter. Deimos, the outer moon, only had a diameter of five miles. Both moons had nearly circular orbits.
Since the two moons of Mars were very small, it was thought that, perhaps, they were not natural satellites at all. It was suggested that they were actually artificial satellites of enormous size, or hollow space stations built by the Martians to live in as the surface of Mars was now becoming uninhabitable.
However, in the fall of 1971 that view of the Martian moons changed as an unmanned spacecraft named Mariner 9 orbited Mars and photographed the planet and its two satellites as well as sending back a wealth of information. Mariner 9 was launched by the United States.
Both Phobos and Deimos, it was learned, were potato shaped. Phobos, the inner moon was found to be about 16.78 miles long, 13.67 miles wide, and 11.19 miles in depth. It orbited Mars at an altitude of only 3,600 miles from the surface.
Deimos, the outer moon had dimensions of 9.32 miles by 7.58 miles by 6.46 miles. It orbited Mars at an altitude of 12,000 miles above is surface.
Both moons are heavily cratered, and are believed to be captured from the asteroid belt. Phobos has a number of parallel grooves. Deimos has a thick layer of dust on its surface which covers many of its surface features.
If you were fortunate enough to set foot on the surface of Deimos, you would need to be careful not to move too fast. The escape velocity on its surface is only 12.53 miles per hour.
This means that if you could run a 100 meter dash in 17.857 seconds or faster, and took a leap, you would fly off of its surface like superman never to return unless your spacesuit had a manned maneuvering unit (MMU) attached to it.
On the larger moon, Phobos, you would need to be able to run a 100 meter dash in 8.850 seconds or faster in order to escape its gravitational pull. No human has run a 100 meter dash this fast yet! However, one could easily throw a baseball away from either Phobos or Deimos if you were on the surface of either moon.