WHEN the Stardust spacecraft plunged through the coma of comet Wild 2 on 2 January, it was in much greater danger than anyone had suspected.
Stardust鈥檚 unprecedented close-up look at the inner regions of the dust and gas cloud, or coma, surrounding the comet鈥檚 nucleus revealed that Wild 2鈥檚 jets are far more numerous and contain far larger solid chunks than most scientists had guessed.
At the high speed of the encounter, around 22,000 kilometres per hour, these larger pieces could easily have smashed into the craft and left it disabled and perhaps wrecked, the mission鈥檚 chief scientist, Donald Brownlee, reported last week at the Lunar and Planetary Science Conference in Houston, Texas.
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Brownlee, who is based at Washington University in St Louis, Missouri, said that most astronomers had thought comets produce just one or two plumes of vaporising gas from their sun-warmed surfaces. However, the images from Stardust reveal dozens of jets, including some emanating from the dark side, which is much cooler. The image below shows a short-exposure image of the comet鈥檚 pockmarked surface, laid over a longer-exposure picture in which the jets are visible.
Instead of smoke-sized or sand-sized particles within the gas, as expected, there were some chunks as big as boulders. 鈥淗ad we known that comets work like this, we would have been terrified,鈥� says Brownlee.