[X] My Assistant

[nprev]

A small lake in Siberia may be a secondary impact feature from the famous 1908 Tunguska event:

http://www.blackwell-synergy.com/doi/full/...2.x?cookieSet=1

[dvandorn]

I know -- same here. And the physical effects found at the site all indicate an airburst-type explosion.

Now, one other airburst explosion that we know of has occurred since Tunguska, though it was a much, much smaller bolide that exploded. I'm referring to the Tagish Lake meteor. That meteor did scatter a lot of material on the ground (well, specifically on the surface of a frozen lake) below the airburst. So we have evidence that such airburst-style bolide impacts don't vaporize the entire impactor as they explode.

Perhaps the Tunguska impactor exploded in the air but some of the mass survived the airburst and struck the ground. That impact would have occurred along the ballistic trajectory of the impactor and not in the center of the airburst-generated blast zone, so it would make sense for it to be somewhat offset from the center of that blast zone. Which is supposedly what is being claimed here.

We just don't have a very good concept of how various types of impactors behave under extreme entry heating conditions. We know generally what can happen from looking at the few such events that have occurred on Earth during human history, and looking at the resulting impact effects of even older bolide strikes. But we don't know the exact composition of the various impactors that have been observed; we have a very poor idea of the composition of airburst impactors, especially. I can well imagine that impactors relatively enriched in volatiles would be more likely to explode before they hit the ground, but we don't know how such bodies are organized before they hit our atmosphere. So, if a large cometary fragment should strike us, it's possible that the volatiles would be irregularly distributed within the mass and while a portion of the mass might explode in the air, another portion might be less enriched in volatiles and thus continue on to a ground impact.

We just don't have enough data to be able to model that kind of thing. Yet.

-the other Doug