Mars Global Surveyor Celebrates Discovery of Deimos
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Mars Global Surveyor Celebrates Discovery of Deimos

October 20, 2009
One might say that today is Deimos' birthday. To celebrate, we present here the first and only Mars Global Surveyor (MGS) Mars Orbiter Camera (MOC) image of this tiny moon. Deimos was discovered 129 years ago on 11 August 1877 (U.S. time, it was 12 August UTC), by U.S. astronomer Asaph Hall. It was the first of two major discoveries that he made that month; less than a week later, he found the other, inner martian satellite, Phobos.

About a month before the 129th anniversary of its discovery, on 10 July 2006, Mars Global Surveyor was pointed away from the martian surface, out toward distant Deimos. Imaging the smaller of the two martian moons was the result of a combined effort between MGS engineers at Lockheed Martin Astronautics and MOC operations engineers at Malin Space Science Systems. When the picture was acquired, Deimos was about 22,985 kilometers (14,285 miles) from MGS. This results in an image of approximately 95 meters (about 312 feet) per pixel. Higher resolution images were obtained by the Viking orbiters in the 1970s - some of those pictures were so good that boulders could be resolved on the moon's surface. While the MOC image is at a lower resolution than the Viking data, acquiring an image of Deimos helps refine the understanding of the tiny moon's orbit and geography. The two craters, Voltaire and Swift, are presently the only craters with names on all of Deimos. Author Jonathan Swift, in his 1726 Gulliver's Travels, had coincidentally surmised that Mars has two moons. Sunlight illuminates the scene from the upper right.

MGS previously imaged the inner, larger moon, Phobos, on several occasions in 1998 and 2003. In 1998, MGS was in an elliptical orbit that permitted the spacecraft to actually fly past the moon; this was not done for Deimos because MGS hasn't been out past the orbit of Deimos since it arrived at the red planet in 1997.

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