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MOONS OF MARS

PHOBOS

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.

DEIMOS

Deimos is as unique and interesting as Mars itself, and therefore there are quite a few fun facts to be learned. Here are some of the most interesting: 

• Like an Asteroid – Deimos is a fairly small moon and looks a lot more like an asteroid than a real moon. Its largest measurement is 15 kilometers and is made with the same kind of rock and minerals that are found on both asteroids and meteorites

• Where Did It Come From? – Because Deimos is made from the same materials as many asteroids, some scientists think that both Deimos and Phobos used to be asteroids in the asteroid belt. Another theory is that Mars was once surrounded by many rocks the same size and shape as Deimos that have disappeared over time.

• Craters – Deimos has far fewer craters than its brother moon Phobos. The two biggest craters are about 1 and 2 kilometers across and are named Swift and Voltaire. The names come from famous writers who once wrote about the possible existence of moons around Mars. Jonathan Swift actually wrote that there were two moons well before they were actually discovered.

• Distance from Mars – Deimos is a lot farther from Mars than Phobos. In fact, it is so far from Mars that it looks like a star in the sky most of the time. From some places on Mars, you wouldn’t even be able to see Deimos at all.

• When Does it Rise? – Deimos rises in the east and sets in the west, but it does so at a strange speed. Instead of rising every night like our moon, Deimos rises only once every 2.7 days.

•  In Front of the Sun – Solar eclipses on Earth are rare. When they happen, we get fairly excited and it is reported in the news for days. However, on Mars, Deimos regularly passes in front of the sun. Since it is so small, it only appears as a small black dot, but it has been recorded multiple times by landers on Mars.

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