Lunar Prospector's demise, scheduled for 5:51 a.m. EDT Saturday , will be watched by about two dozen observatories, including the orbiting Hubble Space Telescope, and hundreds of amateur astronomers. Scientists are hoping the crash will send up a cloud of icy dust that can be scrutinized for signs of water vapor.
Lunar Prospector has spent the last 18 months studying the moon's geology. In March 1998, scientists announced Lunar Prospector had detected evidence of large deposits of frozen water in craters at the moon's poles - about 6 billion metric tons of it, enough to support lunar colonies or manufacturing facilities on the moon.
Not everyone accepted the finding, however, arguing that the hydrogen found by the probe was not necessarily bound up in water molecules. Rather, the hydrogen could be hydrated minerals or absorbed solar wind. Scientists at the University of Texas proposed a radical way to end the debate. With Lunar Prospector running out of fuel and fated to crash into the moon, why not chose its resting spot and kick up a cloud of lunar dust to be analyzed on Earth?
Months of preparation nearly came to a quick end on Wednesday, when Lunar Prospector spent several hours in Earth's shadow, deprived of sunlight for its dying batteries.
"The spacecraft got very cold and it took quite a while to get it warmed up," said Lisa Chu-Thielbar, an education specialist with the Lunar Prospector program. However, by Wednesday night, it was back at normal operating temperatures , accepting commands and appeared healthy enough for its dramatic scientific finale.
Lunar Prospector's grave will be a 31- to 38-mile wide crater on the moon's south pole, visible from Earth but with a ridge high enough to keep it in permanent shadow. To prepare for its plunge, the spacecraft, which has been orbiting about 19 miles above the lunar surface, will be moved out to a 156-mile high orbit.
With a final burn of its maneuvering engine, the probe will travel from the equatorial region above the far side of the moon to the crater on the southern pole, building up enough speed to impact with the force of a 2-ton car crashing at 1,100 mph.
Scientists hope about 40 pounds of water vapor will be stirred up by the impact, although how visible the plume would be on Earth depends on our weather and other factors.
The chance of success is not great, but with Lunar Prospector close to an end, anyway, there is no risk and the potential scientific payoff is tremendous, says NASA research director Guenter Riegler.
"It seems fitting to give Lunar Prospector the chance to provide scientific data right up to the end of its highly successful mission," he said.
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