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There’s no need to worry about being wiped out by giant waves caused by an asteroid hitting the ocean. Although asteroids less than 100 metres across wouldn’t be big enough to destroy civilisation, the fear was that if they crashed into the sea, they could trigger tsunamis that would devastate coastal communities. But that’s not likely, says Jay Melosh of the University of Arizona. Speaking at last week’s Lunar and Planetary Science conference in Houston, Melosh revealed a long-forgotten study by the US Navy, recently unearthed by a librarian at the University of California in San Diego. The report gives the results of test explosions in a Californian lake that closely match the effects of a typical asteroid strike. The waves were much closer together than tsunamis, making them more likely to die out over a short distance or break on the continental shelf far from land.