Deimos not only orbits Mars much further away than Phobos, it is also smaller about half the size , making it very faint in the sky. Although it is made from similar materials to Phobos, and other asteroids, it is much less cratered on the surface, meaning it has been hits by space debris less frequently.
Latest Gallery Images. Moogega Stricker. We on Earth have just one moon, but some planets have dozens of them. Up first are Mercury and Venus. Neither of them has a moon.
Any moon would most likely crash into Mercury or maybe go into orbit around the Sun and eventually get pulled into it. Mars has two moons. Deimos orbits much farther away, tending to stay 12, miles 20, km from the red planet's surface. The moon takes about 30 hours, a little over a Martian day, to travel around its host. Because of their odd shapes and strange composition, scientists thought for a long time that both moons were born asteroids.
Jupiter's gravity could have nudged them into orbit around Mars, allowing the red planet to capture them. But the orbits of the moons make such a birth appear unlikely. Both moons take stable, nearly circular paths around the red planet. Captured bodies tend to move more erratically. An atmosphere could have slowed the pair down and settled them into their present-day orbits, but the air on the Martian planet is thin and insufficient for such a task.
It is possible that the moons formed like the planet, from debris left over from the creation of Mars. Gravity could have drawn the remaining rocks into the two oddly shaped bodies.
Or, the moons could have spawned from a violent birth, much like Earth's moon. A collision, common in the early solar system, could have blown chunks of the red planet into space, and gravity may have pulled them together into the moons. Similarly, an early moon of Mars could have been impacted by a large object, leaving Phobos and Deimos as the only remaining bits. A recent proposal combines the last two possibilities.
They are among the darker objects in the solar system. The moons appear to be made of carbon-rich rock mixed with ice. Because it orbits Mars faster than the planet itself rotates, it is slowly spiraling inward. As a result, scientists estimate that in the next million years or so, it will get so low that the Martian gravity will tear Phobos into a pile of rocks.
And then a few million years later, those rocks will crash down on the surface of Mars in a spectacular string of impacts. Phobos and Deimos both appear to be composed of C-type rock, similar to blackish carbonaceous chondrite asteroids.
This family of asteroids is extremely old, dating back to the formation of the Solar System. Hence, it is likely that they were acquired by Mars very early in its history. Phobos is heavily cratered from eons worth of impacts from meteors with three large craters dominating the surface.
The largest crater is Stickney visible in the photo above. The Stickney crater is 10 km in diameter, which is almost half of the average diameter of Phobos itself.
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