Happy Tunguskaversary!

It's the Centennial of the mysterious Tunguska Explosion, which flattened something like 80 million trees in Siberia on 30 June, 2008 (Click the link to see Andrew's summary of the whole story). Most people agree now that this was caused by an asteroid or comet blowing up as it entered the atmosphere - but not until it was only a few km above the surface of the earth. "Impacts" such as this leave no crater, and no trace at all if over the ocean. Maybe there are a lot more dangerous impactors entering the atmosphere than we know about! the Sandia super computers who have calculated that the asteroid or comet which exploded was much smaller than previously thought. The drawback to this, of course, is that the frequency of smaller objects is greater (see this NEO size frequency diagram). Party on!