Tuguska Explosion: 100 Years Later, Still UnsolvedS

One hundred years ago today, June 30th, 1908, a great explosion rained Hell over Siberia, flattening 830 square miles of forest. Easily big enough to destroy a city, the 30-meter diameter space rock missed Moscow by about 4 hours. And it will happen again. But even as we track the objects headed our way in the next century, the flood of media hype over the centennial this past week shows there are still some major mysteries about the Russian blast that need solving.

USA Today, New Scientist, the awesome astronomy blog Bad Astronomy and the BBC and Nature and just about every sciency news outlet all have items devoted to the centennial. But they disagree on what the Tunguska Event was. USA Today calls it an "impact,' but Bad Astronomy says "air blast" and says there's no evidence anything hit the ground. New Scientist has posted a video in which their reporter circles Lake Cheko nearby the blast site in a helicopter and speculates whether it's the smoking gun of an impact.

What's going on here? Tunguska is probably the most heavily studied impact/air blast/space rock encounter on Earth and we know almost nothing about how it happened. It's also hard to say how likely it is that it will happen again, though one scientist's guess isn't comforting:

In terms of risk to Earth, astronomer David Morrison of NASA's Ames Research Center says a Tunguska-magnitude strike could happen once every two centuries and a bigger impact, a "civilization-threatening" million-megaton strike, could happen once every 2 million years. Even though astronomers have spotted more of these nearby asteroids in the last two decades, the estimated odds of an impact have actually declined, as Morrison notes in a May issue of NEO News, his asteroid newsletter.

If Morrison's right, we've got at best another century to learn as much as we can from Tunguska before another similar event hits home - maybe less. And in the mean time, we'll have plenty of close calls reminding us that we are basically sitting ducks unless we start doing something about one of the greatest threats to our survival as a civilization.