Mars Moons Phobos and Deimos Photographed Together

The Martian moons Phobos and Deimos have been photographed in the same frame for the first time.

The European Space Agency's Mars Express orbiter snapped a series of images of the two diminutive moons on Nov. 5 and released the pictures today.

The images will help researchers refine models of the two moons' orbits, but mostly they'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 miles long (27 km). Phobos orbits Mars in an almost circular equatorial orbit at a distance of 3,728 miles (6000 km). It circles Mars every 7 hours and 39 minutes, traveling faster relative to Mars than does Earth's moon relative to our planet.

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

Deimos, too, is not spherical. It has an average diameter of 8 miles (13 kilometers). It orbits Mars at a distance of roughly 12,427 miles (20,000 km). On the surface of 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 and rims, similar to those found on larger objects.

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

Scientists aren't sure about the origins of these moons. They might be captured asteroids, or perhaps they are leftovers 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