IN the summer of 1908, an object from space created a tremendous explosion over Tunguska in central Siberia. Most scientists believe the object was a rocky asteroid—yet no crater or debris has ever been found. Now a Russian scientist has come up with new calculations that strongly support the asteroid theory and confirm what others had suspected: that the heat from the explosion consumed the fragments of the asteroid, leaving only microscopic debris.
Until three years ago, many scientists believed that the object must have been a comet—which would have exploded high above the Earth and done less damage than an asteroid. But that theory was dealt a serious blow in 1993, when Christopher Chyba, now at Princeton University, Kevin Zahnle of the NASA Ames Research Center in California, and others, created computer simulations to explain the pattern of trees blown down by the explosion. Their calculations of the explosion's force suggested that the body involved was a stony asteroid about 40 metres in diameter, travelling at 15 kilometres per second (
Now Vladimir Svetsov of the Institute for Dynamics of Geospheres in Moscow has re-examined the American team's data to estimate the heat of the explosion. He found that the air around the body would have been heated to 15 000 °C, enough to melt the surface of the rocky fragments. Droplets would then be stripped off the fragments until nothing remained. "It was very similar to a nuclear explosion," says Svetsov (
The microscopic debris was probably scattered over a wide area by the turbulent wake of the asteroid, says Svetlov. The droplets could explain the origin of spherical particles found in tree resin near the impact site, which are thought to be extraterrestrial.
All comments should respect the New Scientist House Rules. If you think a particular comment breaks these rules then please use the "Report" link in that comment to report it to us.
If you are having a technical problem posting a comment, please contact technical support.
18:53 05 September 2008
