Artist's concept of Mars and it's moon, Dione. - stock illustration

Artist' concept showing Mars and its even smaller satellite Deimos might appear from a distance of about 100 miles from the surface of Deimos. Deimos is seen passing over Acidalia Planitia, an albedo feature that has been observed by Earth09/14/2009bound astronomers since the 19th century. To the southwest are the fog09/14/2009filled canyons of Valles Marineris, the westernmost of which are still in darkness. Beyond Mars, immediately to the left of its night side, is Phobos at a distance of 20,000 miles. The two bright objects in the lower left are the stars Beta Gruis and Al Nair in the southern constellation Grus. Deimos does not possess enough mass to pull itself into a sphere. Its shape is oblong with a length of about 10 miles and only 6 miles wide at its smallest dimension. Orbiting 14,600 miles above Mars' surface, Deimos completes one revolution every 30 hours.