Cool Phobos Facts and Images

Phobos orbits just 3,700 miles (6,000 kilometers) from Mars, on average. No moon in our solar system is closer to its host planet. And it is getting closer.

The 14-mile- (23-kilometer-) wide moon is snuggling up to Mars at a rate of 6 feet (1.8 meters) every 100 years. In about 50 million years, the moon will crash into Mars. Or, scientists say, the gravitational force of the Red Planet might tear the moon apart. If that happens, the shreds of Phobos could form a ring around Mars, similar to the rings around Saturn.

An impact long ago left a big crater on Phobos -- 6 miles (10 kilometers) wide -- called Stickney. Streaks of material ejected by the impact can be seen across the moon's surface. Stickney appears to be filled with dust, and boulders look to be sliding down its sloped surface.

Like Mars' other moon, Deimos, Phobos has a thick layer of regolith, or dust and rock. It is thought to be especially thick on Phobos -- up to 330 feet (100 meters). Researchers think the regolith was created when other space rocks slammed into the moon, pounding it into powder. But scientists are stumped as to how the material stuck to an object that has almost no gravity.

Scientists say that when the Sun shines on Phobos, the temperature is not unlike a pleasant winter day in Chicago. But just around the corner, on the dark side of the tiny moon, the thermometer can plunge to an extreme Arctic minus 170 degrees Fahrenheit (minus 112 Celsius).

From Mars, Phobos would appear about one-third as big as Earth's moon. But since it isn't round, lovers on Mars would stand hand-in-hand, staring up at a shiny potato. More about Phobos in our Reference Section.

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