ONE of the largest impact craters on Earth was probably caused by a comet strike rather than an asteroid. If so, the crater could have provided ideal conditions for life to flourish.
Susan Kieffer and her team at the University of Illinois in Urbana-Champaign compared the rock structure and composition in and around two of the world鈥檚 largest craters. The first, a 65-million-year-old crater at Chicxulub on the Yucatan peninsular in Mexico, is widely believed to be the site of the impact that wiped out the dinosaurs. The other crater, in Sudbury, Ontario, dates back to 1.8 billion years ago.
Kieffer found that while the two craters were similar in size 鈥� around 200 kilometres across, with a series of concentric ripples of rock encircling them 鈥� there were also clear differences. The heat produced from the impact at Sudbury created about 31,000 cubic kilometres of molten rock, around 70 per cent more than at Chicxulub. And unlike the impact at Chicxulub, the crater at Sudbury is known to have given rise to a network of fissures of warm water.
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Kieffer plugged the measurements taken from the craters into a computer model that contained data on typical comet and asteroid characteristics, such as their composition and speed. The model showed that the size of the crater and the amount of rock melting at Chicxulub was most likely due to a 13-kilometre-wide asteroid striking at around 25 kilometres per second. The crater at Sudbury, though, was more likely to be caused by an ice-rich comet of similar size, travelling nearly twice as fast. The comet鈥檚 body could have added up to 2000 cubic kilometres of water to the melt at Sudbury.
The larger amount of heat produced by the Sudbury impact would have powered the circulation of hot water at the site, says Kieffer. This could have made it a likely place for life to thrive.
Kieffer says the results could help astrobiologists identify regions on Mars that might also once have been havens for life. 鈥淥ur next step is to take what we鈥檝e learned about Sudbury and apply it to Mars,鈥� she says.
