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One of the Moons of Mars Orbits Around the Red Planet Much Faster That It Rotates. It Completes an Orbit in Just 7 Hours and 39 Minutes.

Mars has two moons: Phobos and Deimos. American astronomer Asaph Hall was discovered in August 1877 and named after the Greek mythological twin characters Phobos (fear and panic) and Deimos (terror and dread). They accompanied their father, Ares, into battle. The Romans called Ares, the god of war, Mars. But do you know fast Phobos orbits around Mars?

One of Mars’ moons orbits the planet much faster than Mars rotates, completing an orbit in just 7 hours and 39 minutes. It appears to rise in the west, move across the sky in 4 hours and 15 minutes, and set in the east twice per Martian day.

What are the Two Moons of Mars?

In Greek mythology, Phobos is one of Ares’ (Mars’) and Aphrodite’s sons (Venus). The word Phobos is Greek for fear. It is also the root of the word phobia.

Hall discovered it on August 18, 1877, and photographed it with Mariner 9, Viking 1, and Phobos in 1971, 1977, and 1988.

It is widely assumed that Phobos and Deimos are captured asteroids. Some believe they formed in the outer solar system rather than in the main asteroid belt.

If ice is confirmed, Phobos and Deimos may someday be useful as space stations from which to study Mars or as intermediate stops to and from the Martian surface. (Source: Space)

How Does Phobos Orbit Around Mars?

Phobos orbits Mars at a distance less than the synchronous orbit radius. As a result, it rises in the west, moves quickly across the sky, and sets in the east twice a day. It’s so close to the surface that it can’t be seen above the horizon from anywhere on Mars.

And Phobos is doomed: because its orbit is lower than the synchronous altitude, tidal forces are lowering it. Current rate: about 1.8 meters per century. It will either crash onto the surface of Mars or break into a ring in about 50 million years. This is the inverse effect of the effect operating to raise the Moon’s orbit.

Phobos and Deimos, like C-type asteroids, could be made of carbon-rich rock. Their densities, however, are so low that they cannot be pure rock. They are most likely made of a combination of rock and ice. Both have a lot of craters. According to new images from Mars Global Surveyor, Phobos is covered in a layer of fine dust about a meter thick, similar to Earth’s moon regolith. (Source: Space)

The Discovery of Phobos

Phobos was discovered in the United States Naval Observatory in Washington DC by Asaph Hall, six days after its more diminutive sibling Deimos was found.

The astronomer studied the region around Mars with a 26-inch refractor. He discovered the smaller moons orbiting the planet’s equator by checking it closer than any other scientist. (Source: Space)

How Did Phobos Get Its Name?

Like many planets and moons in our Solar System, the small satellite derives its name from Greek mythology. Phobos, the god of fear in Homer’s epic poem The Iliad, inspired the moon’s name. He is Ares’ (Mars’) and Aphrodite’s son (Venus). (Source: Space)

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