Mars, the red planet named for the Roman god of war, has two tiny moons, Phobos and Deimos, whose names are derived from the Greek for Fear and Panic. These martian moons re probably asteroids from the main belt between Mars and Jupiter or possibly from further out in the Solar System. Phobos, the larger of the two, is revealed as a cratered, asteroid-like object in this image from the Mars Reconnaissance Orbiter. Phobos’ orbit is so close to Mars—about 5,800 km above the surface compared to 400,000 km for our Moon—that gravitational tidal forces are dragging it down. In 100 million years or so, Phobos will likely be shattered by stress caused by the relentless tidal forces, the debris forming a decaying ring around Mars.
Image Credit: NASA