What caused the 1908 explosion at Tunguska in Siberia?

Question

The most promising theory seems to be that it was caused by an asteroid that exploded above the ground before it could land. This would have knocked down all the trees. There was no crater, and the flash could be seen for 400 miles away.

Answer 1

Low density comet hitting the ground. High impact, low-ish mass, mainly dust and ice, resulting in small or flat crater and a lot of energy dicharged outward, flattening trees for miles. An exploding asteroid would have resulted in large chunks of rock hitting the ground, unless it vaporised completely, highly unlikely.

Answer 2

A big comet fragment would actually deposit most of its kinetic energy in the atmosphere (think fluffy snowball impacting a lake at high speed; most of the kinetic energy is released in the top layer of the water as the snowball splatters) creating a ground blast pattern very much like Tunguska. You can read about this splattering effect in a neat paper by Kevin Zahnle when he was trying to predict what would happen when Shoemaker-Levy 9 fragments impacted Jupiter's atmosphere. Nearly all the energy was deposited at pressures of 10 bar or less. This was for a 1km fragment. A smaller fragment splatters higher.

The first reference hits the SL-9 paper. The second is referenced in that paper (and I was unaware of it) and actually tries to model the Tunguska event!

Answer 3

Siberia 1908 Explosion

Answer 4

I have posted a great video about this at http://spacegeek.org, Tunguska is addressed half-way in the video.

Answer 5

Several theories See

http://en.wikipedia.org/wiki/Tunguska_event

Answer 6

What's the question? It seems you already know what was going on there.