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Mars has two moons. The first of these moons is Phobos, named for a character in the legendary piece of Greek literature, The Iliad. Phobos was discovered in 1877 by Asaph Hall and at first glance looks very little like our moon we see every night above the trees.

What makes Phobos different from Earth’s very round moon? There are a few details that will help us better understand:

  • Phobos is Close – Phobos orbits closer to Mars than any other Moon in the solar system. That means, of all the moons orbiting Jupiter, Saturn, Neptune and beyond, none are closer to their planets than Phobos is to Mars.
  • Rise and Fall – Because Phobos is so close to Mars, it only takes 4 hours and 15 minutes to cross the sky. Because it is so close to Mars, some believe that in a few million years, Phobos might crash into the surface of Mars or even break apart. 
  • Like an Asteroid – No one knows where Phobos came from, but it looks very similar to an asteroid. It reflects very little light so getting a good picture of it is hard, but it’s clear that Phobos isn’t round like our moon. In fact, it is rather lumpy shaped, with a number of large craters.
  • Gravity Changes – Because Phobos isn’t shaped like a normal planet or moon, it has strange gravity. In some cases, the gravity can more than double. You don’t want to be walking on this moon when the gravity increases!
  • Craters Galore! – Phobos is covered in craters. The largest crater is Stickney, which is thought to have almost destroyed the moon entirely. Many of the other craters on Phobos are named after characters in the story Gulliver’s Travels including Clustril, Drunlo, Flimnap, Grildrig, and of course Gulliver.
  • Pictures of Phobos – The first real photograph of Phobos was taken by the Mariner 9 spacecraft in 1971. Since then, it has been photographed eight more times by Viking 1, the Mars Global Surveyor and the Mars Reconnaissance Orbiter. Two probes were sent to Phobos by the Soviet Union in 1988, but neither was able to gather any information. A new mission to Phobos is being planned by Russia for later in 2011 called Phobos-Grunt.
  • Hollow?! – In the 1950s, some astronomers believed that Phobos might be hollow. It turned out to be false, but for the better part of ten years, some very prominent scientists believed that Phobos could have been created by Martians.

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Useful Links

More Information on NASA website

Nice photos of Phobos

Video of Phobos (click on the file to watch or download)