How Mars’ Moon Phobos Captures Our Imaginations

For a small, lumpy chunk of rock that barely reflects any light, Mars’ Moon Phobos draws a lot of attention. Maybe because it’s one of only two moons to orbit the planet, and its origins are unclear. But some of the attention is probably because we have such great images of it.

Phobos is the largest of Mars’ two moons, the other one being Deimos. Scientists are uncertain about their history. They could be a pair of captured main-belt asteroids, two lobes of what once was a binary asteroid until capture separated them, or a second-generation object formed after Mars had already formed. Or they could be surviving fragments from an ancient collision between more massive objects.

Phobos isn’t very large. It’s about 26 km × 23 km × 18 km and not massive enough to be rounded. Studies of its density show that it’s a rubble-pile body loosely held together by its own gravity.

When the ESA launched its Mars Express Orbiter in 2003, its mission was to study Mars. One of its instruments is the High-Resolution Stereo Camera, a German contribution that produces colour images with up to two meters resolution. The instrument also has a black-and-white mode, and the original image of Phobos was black-and-white.

Leave a Comment