Luna 49 - Summer 1999

Lunar Prospector's chilling demise

Lunar Prospector now nears the completion of its 18 month mission. During this time a wealth of new insights into the nature of the Moon have resulted. Most notable among its findings has been the apparent confirmation of the presence of vast quantities of water ice within permanently shadow filled craters at the Moon's north and south poles. As the spacecraft approaches the end of its useful lifetime, a final, bold experiment will attempt to prise the last gem of knowledge out of this highly successful mission. A science team led by David Golstein of the University of Texas will command the probe to smash into a permanently shadowed south pole crater. If all goes to plan, a direct signal of water could be observed by land and space based telescopes.

Path of Lunar Prospector's terminal plunge.

Lunar Prospector has been orbiting the Moon at an altitude of about 30 km, gathering geological data through its instruments. Now that Prospector's useful life approaches an end, the probe will be crashed in a controlled manner into a permanently shadowed south polar crater on 31 July at 21:51 UT. Scientists hope that a plume of water vapour will be thrown above the Moon's surface - an object that could be observed from Earth in order to confirm that water ice really does exist on the lunar surface.

The impact energy of the 160 kg probe, slamming into the Moon at 1.3 km/s will be roughly equivalent to a small helicopter crash at a speed of 2,500 km/h, and might liberate enough water vapour to be detected by ground and space-based observatories. It is thought that the plume might be visible optically, although normal amateur visual observation may prove fruitless. A positive spectral detection of water vapour or its photo-dissociated byproduct, OH, would be definite proof of water ice.

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