Tunguska: Burn the Evidence

Whatever fell from the sky and exploded in the Tunguska region of central Siberia on 30 June 1908 left thousands of trees charred and blown down over a 2000-square-kilometer area. But it deposited no sizable debris--be it chunks of a meteorite or cometary dust. Now scientists have a good idea why: An analysis published in the 24 October Nature suggests that the heat from an exploding meteorite would have incinerated nearly all the resulting debris.

Computer models have suggested that the culprit was a meteorite that explosively fragmented into tiny pieces of rock about 10 kilometers above the ground. Now Vladimir Svetsov, a mathematician at the Institute for Dynamics of Geospheres in Moscow, has provided mathematical support for that scenario. Svetsov calculated the intricate heat transfer from an exploding stony meteorite to the atmosphere and determined that the atmosphere would grow hot enough--to about 6000 degrees Celsius--to completely burn up the meteorite fragments.

"Svetsov's work is fundamentally right," says Kevin Zahnle, a space scientist at the NASA Ames Research Center in California and co-author of a leading theory on meteorite fragmentation over Tunguska. The next step will be to try to better identify what kind of meteorite was to blame, Zahnle says. He's laying his money on the fact that it was an atypical meteorite--perhaps, he says, even a chunk of Mars.