June 30th was the 100th anniversary of the Tunguska blast in Siberia. (Google for "Tunguska Event" as there is far too much material to link here...) General estimates of the blast put it at 10 to 15 megatons (though some now argue 3 to 5 megatons), or about 1,000 times the Hiroshima detonation. 830 square miles of trees were flattened. Windows shattered 250 miles from the blast center. The fluctuations in air pressure were measured in England, thousands of miles away.In short, it was one hell of a bang.No crater was left behind, making it likely that it was a meteor or asteroid, maybe even a small comet burst in mid air.The problem is, aside from tree damage, we have no physical evidence of the "object", if there really was one. Basically, we don't have a clue at this point, but it's fun to speculate. You can certainly spend hours reading every take on it.