The Moons of Mars

Moons of Mars

Although Mars is close to the Earth and has fascinated humans for thousands of years, it took a very long time to discover that the Red Planet has satellites. While Galileo discovered four moons around distant Jupiter in 1610, it wasn't until August 1877 that the moons of Mars were found.

The person who found them was Asaph Hall, an American astronomer working at the US Naval Observatory in Washington, D.C. And he came very close to missing his chance at fame. He had grown so frustrated looking for moons around Mars that he was on the verge of quitting.

Asaph Hall Discovered Moons of Mars

Professor Asaph Hall discovered the Moons of Mars

Fortunately, his wife Angelina urged him to continue. The next night, he discovered a small moon around Mars and, six days later, a larger one. The larger moon was named Phobos (fear) and the smaller one Deimos (dread). These worlds honored the two sons of Ares, who is the Greek equivalent of Mars, the Roman god of war.

Moons of Mars

Moons of Mars: Deimos and Phobos

Despite increasingly powerful telescopes, the moons of Mars remained enigmas due to their small sizes and dark, non-reflective surfaces. It was not until NASA's Mariner 9 became the first spacecraft to orbit the planet that scientists were able to explore the two moons in depth. And what interesting stories the moon told.

Phobos' surface is dominated by a 9 km (5.6 miles) crater, which astronomers dubbed Stickney after the maiden name of Angelina Hall. The little moon's gravity is very slight: a person weighing 68 kg (150 lbs) on Earth would about 68 grams (2 ounces) on Phobos. A person could probably jump off the moon.

The moon, which has a diameter of 22.2 km (13.9 miles), orbits a mere 9,377 km (5,827 miles) above the Martian surface. This is the closest that any moon is known to orbit a planet. The satellite is so fast that it circles the planet three times per day.

Phobos is slowly moving toward Mars; it will eventually crash into the surface or break up into a ring. This may have happened before; a string of craters along the equator suggest that other moons suffered the same fate.
Deimos orbits at a distance of 23,460 km (14,663 miles) and takes about 30 hours to circle Mars. The moon, which has a diameter of 12.6 km (7.9 miles), is smoother than Phobos. It is composed of porous, low-density rock rich with carbonaceous material, making it similar to a C-type asteroid. Unlike Phobos, Deimos is being slowly pulled away from Mars.


Some scientists to believe that both Deimos and Phobos are captured worlds from the Asteroid Belt. This is a controversial theory, however. Other scientists believe that Phobos formed at the same time as Mars but that Deimos might be an asteroid.

Learn More About The Moons of Mars

Mars: Moons

The Mysterious Moons of Mars

 

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