COMETS are supposed to be lumps of icy rubble covered in dark dust. But the most detailed images ever taken of a comet have revealed some surprising complexity.
In January, NASA鈥檚 Stardust spacecraft flew to within 236 kilometres of Comet Wild 2 and took 72 pictures of the comet鈥檚 nucleus. Detailed analyses of the images reveal steep-walled craters, spires, and pinnacles up to 100 metres high, and dozens of jets spewing gas and dust. 鈥淲e were totally stunned by what we saw,鈥� said Stardust principal investigator Donald Brownlee, of the University of Washington in Seattle, at a NASA press conference in Washington DC last week.
The presence of the pinnacles shows that at least 100 metres of material has been eroded from the surface of the comet鈥檚 nucleus, which is about 4.5 kilometres in diameter, and the sharply carved features suggest the surface is harder than an icy snowball (Science, vol 304, p 1764, 1769, 1774 and 1776).
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Instruments on board Stardust have confirmed that the comet鈥檚 dust particles contain high levels of organic compounds, supporting theories that comets may have dumped organic material on Earth, helping life get started.
The spacecraft will bring back the first-ever samples of cometary dust in a capsule, which will be dropped over the Utah desert in January 2006.