Mars Moons Phobos and Deimos Photographed Together

TheMartian moons Phobos and Deimos have been photographed in the same frame forthe first time.

TheEuropean Space Agency's Mars Express orbiter snapped a seriesof images of the two diminutive moons on Nov. 5 and released the picturestoday.

Theimages will help researchers refine models of the two moons' orbits, but mostlythey're just cool results of a year-long effort to get the timing right.

Phobos,the larger of the two moons, is shaped something like a potato. It is 16 mileslong (27 km). Phobos orbits Mars in an almost circular equatorial orbit at adistance of 3,728 miles (6000 km). It circles Mars every 7 hours and 39minutes, traveling faster relative to Mars than does Earth's moon relative toour planet.

Phobos? found last year to be more like a pileof rubble than a solid object ? is moving closer to Mars at a rate of 6feet (1.8 meters) every 100 years. In about 50 million years, the moon willcrash into Mars.

Deimos,too, is not spherical. It has an average diameter of 8 miles (13 kilometers). Itorbits Mars at a distance of roughly 12,427 miles (20,000 km). On the surfaceof Deimos, the acceleration of gravity is less than 0.1 percent that of Earth.But like Phobos, Deimos has been able to develop landforms, like craters andrims, similar to those found on larger objects.

Phoboswas 7,332 miles (11,800 km) from Mars Express when the images were taken.Deimos was 16,280 miles (26,200 km) away.

Scientistsaren't sure about the originsof these moons. They might be captured asteroids, or perhaps they areleftovers from the formation of Mars, or they might be fragments of Mars,blasted out by the impact of a giant asteroid or comet.

• Video - Two Moons of Mars Seen Together
• Mars in 3D: Images from Mars Express
• More Facts About Phobos and Deimos