As Cool as the Cosmos Duncan Steel Guardian News People expect meteorites to land in a blaze of heat, but they are in fact icy cold, says Duncan Steel Recently a woman walking her dog in York heard a whiz and a bang, and then spotted a smoking hole in the ground. Assuming it was a meteorite impact, the police cordoned off the area and a curator from the York Museum was called in to dig up the supposed cosmic rock. However, it was obvious, even from the sparse initial report, that this was not a visitor from space.
Meteorites are cold when they land, and generally remain intact on the surface.
It proved to be an exploding underground power cable. The chance of an extraterrestrial rock reaching the ground depends critically on its dimensions, different things happening in distinct size regimes. Every year the Earth accumulates about 40,000 tons of cosmic detritus, mostly as billions of tiny flecks ranging in size from sand grains to peas. Travelling at typically 20 miles per second, these are heated and then evaporated by friction with the upper atmosphere, and in their death throes they appear to us as meteors, or shooting stars. This is possible because their relatively high surface areas enable them to lose their energy by radiating it away, whereas larger bodies cannot do this quickly enough, and so are melted and vaporised.