A century ago, something exploded high above the Tunguska River in Siberia. It flattened hundreds of square miles of forest, knocked around some herders and traders, and set off earthquake detectors across Asia and Europe. It also set off a scientific inquest that's still going on.
The subjects of the inquest are the nature of the object that exploded, the power of the blast, and even its effect on the landscape.
The first scientific expeditions didn't visit the site until the 1920s. Scientists found no impact crater, so they concluded that an iron-rich asteroid had exploded above the ground. They found no metals lying on the ground or buried in the swamps and forests, though, so other researchers suggested that the Tunguska object was a small icy comet. But a comet probably would have exploded much higher in the atmosphere. So today, the leading idea says that it was a rocky asteroid that exploded about five miles up.
Most estimates say the asteroid was half as wide as a football field, and weighed several hundred thousand tons. But recent simulations show that it might have been a good bit smaller, and its blast much less powerful than thought.
And just last year, a research team claimed that a small lake near the blast site was a crater carved by the impact of a chunk of the asteroid. But many other scientists disagree, so more expeditions and more simulations may be needed to solve the mysteries of Tunguska.
We'll talk about other asteroid impacts tomorrow.
Script by Damond Benningfield, Copyright 2008
For more skywatching tips, astronomy news, and much more, read StarDate magazine.