Space scientists are planning to punch a hole into a comet to discover what is inside. The mission involves sending a two-part satellite for a rendezvous with Comet P/Temple 1 and then smacking it with a 500kg projectile that will blast a hole as big as a football pitch and as deep as a seven-storey building.
The $240 million mission was conceived by Prof Michael A'Hearn of the University of Maryland and will be launched by NASA in 2004, for arrival at the comet in July 2005. The name chosen for the mission, appropriately enough, is Deep Impact.
The price is considered low-cost by NASA, which has pursued a programme of inexpensive science-rich satellite launches that give the greatest possible information return at the lowest possible price. The satellite will carry a camera and an infrared spectrometer. Once near the comet it will separate, allowing a copper projectile to be fired into the comet at a speed of 10km a second (22,300 m.p.h.). The object is to break away the comet's surface, exposing pristine cometary material underneath. The camera and spectrometer will observe the impact and collect data.
The projectile is made of copper because its spectrographic signature is easily identified and its signal can be discarded, leaving scientists with a good idea of the comet's chemical make-up. Its high speed will cause the projectile to vaporise on impact and it should gouge a hole 25 metres deep and 120 metres across.
The actual impact will be spectacular and observable from the Earth, according to Dr Lucy McFadden, an associate research scientist in the University of Maryland.