NASA Astronomy Picture of the Day: 

You can discover the cosmos with NASA! Each day a different image or photograph of our fascinating universe is featured, along with a brief explanation written by a professional astronomer. This is today's image! Any idea what it is? 

Meet Phobos, a Martian Moon! This is one of the moons that orbit Mars! If you think it looks very dark, you are correct! Phobos is one of the least reflective objects in the entire Solar System! 

MORE ABOUT PHOBOS:

Phobos was discovered on Aug. 17, 1877 by Asaph Hall. Phobos, the largest and innermost of two Martian moons, is also the darkest moon in the entire Solar System! Its unusual orbit and color indicate that it may be a captured asteroid composed of a mixture of ice and dark rock. The featured picture of Phobos near the limb of Mars was captured in 2010 by the robot spacecraft Mars Express currently orbiting Mars. 

Phobos is a barren moon and heavily cratered. A number of the craters have been named, with its largest crater located on the far side. From images like this, Phobos has been determined to be covered by perhaps a meter of loose dust. Phobos orbits so close to Mars that from some places it would appear to rise and set twice a day, but from other places it would not be visible at all. Phobos' orbit around Mars is continually decaying -- it will likely break up with pieces crashing to the Martian surface in about 50 million years.