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21-Oct-2010

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Creating a crater: LCROSS mission finds minerals on the moon



An image of debris, ejected from Cabeus crater and into the sunlight, about 20 seconds after the LCROSS impact. The inset shows a close-up with the direction of the sun and the Earth. [Image courtesy of Science/AAAS]

Last year, a NASA space mission crashed a used rocket into the bottom of a dark crater near the Moon's South Pole. This experiment, known as LCROSS—Lunar Crater Observation and Sensing Satellite—was designed to locate water and other minerals stored in the Moon's soil. Now, this week in Science, researchers describe exactly what happened when that empty shell of a rocket slammed into the Moon's cold surface.

The impact site was Cabeus crater, a "permanently shadowed region" of the Moon that never receives any sunlight. Scientists believe that it is one of the coldest places on the lunar surface. So, when the empty shell of the NASA rocket struck the bottom of Cabeus crater, a large plume of dust, vapor, and other debris was ejected up into the air—and into sunlight for the first time in a long time.

As the debris from the impact became visible in the sunlight, a "shepherding" spacecraft that was traveling behind the rocket was ready to record the event with a variety of cameras, spectrometers, and radiometers. An analysis of data from that shepherding LCROSS spacecraft now provides an estimate of the amount of frozen water on the floor of that cold, dark crater.

In one Science report, Anthony Colaprete and colleagues suggest that about 155 kilograms (342 pounds) of water vapor and ice were blown out of the crater's darkness and into the spacecraft's field of view. They also estimate that about 5.6 percent of the total mass inside of Cabeus crater (plus or minus 2.9 percent) could be made of frozen water alone. Their analysis also identified a number of other minerals that seem to be contained in the soil of the crater.

Another group of researchers, led by Peter Schultz, suggest that the rocket impact created another crater within Cabeus crater that is about 25 to 30 meters wide. They say that somewhere between 4,000 kilograms (8,818 pounds) and 6,000 kilograms (13,228 pounds) of debris, dust, and vapor was blown out of the dark crater and into the sunlight by the rocket.

Taken together, these results from the LCROSS mission provide evidence that permanently shadowed regions of the Moon, like Cabeus crater, can trap volatile compounds—delivered from deep space or other regions of the Moon—including water, and preserve them there for eons.

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This research appears in the 22 October 2010 issue of Science.