After going in circles around our own planet for more than 30 years, astronauts may finally have gotten permission to leave home. In January, President Bush unveiled an ambitious plan for a manned mission to Mars, using the moon as a testing area and stepping-stone. But for many planetary scientists, the moon is a desirable destination in and of itself. Although the Apollo missions brought back nearly 400 kilograms of rocks, scientists still know precious little about the moon's topography, gravitational field, and overall composition.
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