Tunguska

Today is the 100th anniversary of the Tunguska event- one of the largest known meteorite explosions of historical times, if not the largest. The general consensus is that it was some sort of space rock. I've always felt the hypothesis that it was a comet (a ball of dirty ice) made the most sense- the ice would completely vaporize, leaving nothing but some dust. While due to the explosion and devastation of about 800 square miles of trees this is considered an impact, no crater has ever been discovered.

Based on observations made by the first scientific investigation to travel to the area, 19 years afterwards, the blast is estimated to have been in the range of 15 megatons, nearly 1000 times more powerful than the blast over Hiroshima! Based on this figure, it is estimated that the object itself was about 120 feet in diameter and traveling 33,500 miles per hour. These figures are from an article in SpaceDaily (There's another article here). Another site that looks pretty reputable puts the estimate at closer to 60 Hiroshima-sized bombs, and the diameter of the object at 30 meters (roughly a hundred feet). The latter site has some interesting paintings based on eyewitness testimony, and a number of fascinating quotes, usefully translated into English. Wikipedia also has a good article, with some good eyewitness quotes.

So I went looking for some cool pictures to put up with this post and found myself at YouTube. None of these match the Tunguska impact well, but are worth watching. Try to imagine something much less energetic than the first, much more energetic than the second, and much less corporate than the third.

A GREAT BIG one:


A Real one:


A funny one:

Much is made over the Chicxulub impact, generally believed to have killed off the dinosaurs as well as an enormous portion of other species. But the consequences of a relatively "small" impact could be severe. From what I know, I think we would recognize and track an incoming meteorite that was "only" 30 meters in diameter. But how do you think our leadership and military would respond to the utter destruction of an American city if we missed it? This was the basis of a short SF story I read many years ago- Can anyone remind me of the author and the story's name?

Followup:
I've found a couple of pictures linked in the comments at the BadAstronomy post. This post, written by a real astronomer, is well worth reading. Observers noted that trees had been knocked down radially away from the center of the explosion; trees near the center were still standing, but were stripped of their branches and bark. Dead trees here and here. Also a couple of articles at USA Today and BBC