The Mars Express orbiter will skim the surface of Phobos at a distance of just 50 km on March 3, 2010. For comparison, this image of Phobos, taken by NASA, was captured at a distance of 9,670 km.

Mars has two moons: Phobos and Deimos, named for the minor Greek deities Fear and Panic (what could go better with a planet named after a god of war?). On March 3, Mars Express – a Mars orbiter operated by the European Space Agency (ESA) – will set a record for the closest-ever flyby of Phobos when it skims over the moon at a distance of only 50 km (about 30 miles). ESA scientists hope that by venturing so close to the rather lumpy moon, Mars Express can gather data that will help answer lingering questions about Phobos.

Earlier Mars Express flybys have determined the mass and volume of Phobos, using a variety of instruments. Surprisingly, the data suggest that parts of Phobos may actually be hollow. The March 3 flyby should help to either confirm or negate this idea.

Another goal of the flyby is to determine the internal chemical composition of Phobos, in the hopes that such information may help scientists determine the origin of this moon. There are three current theories about Phobos: one, that it is a captured asteroid; two, that it formed at the same time and from the same basic materials as Mars; and three, that it was formed from debris shot into Mars’s orbit by a large meteorite strike.

The Mars Express orbiter is only one of many experiments designed to discover more about our planetary neighbor. If you would like to know more about past, present, and future Mars exploration, come see the live show Mission to Mars, one of two Science 360 shows on MPSC’s spring schedule.

Casey Rawson is the Science Content Developer for Science 360. In case you're wondering, Deimos has also been explored at close range: in 1977, the NASA Viking Orbiter II flew over this moon's surface at a distance of only 30 km.

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