100 Years Since Tunguska

[Monte Davis]

Richard Fiero quotes:

> We know that a rather massive body flew into the atmosphere of our 
> planet, said Boris Shustov of the Russian Academy of 
> Sciences. It measured 40 to 60 meters in diameter. Clearly, 
> it did not consist 
> of iron, otherwise it would have certainly reached the earth...

 That's not as certain and clear-cut as he makes it sound. When something
like that hits an atmosphere, the thermal shock is way outside our
experience, even with spacecraft re-entry: there literally IS NOT TIME for
the air to be pushed out of the way, so a "column" many miles long/deep is
rammed into a layer of dense plasma at stellar temperatures. (It was
seriously suggested in the 1960s that researchers look for traces of
thermonuclear fusion at Tunguska -- no deuterium or magnetic confinement
needed, just good old compression, the way the dark heart of the sun does
it.)

That plasma -- and thousands or millions of atmospheres of pressure -- is
doing its best to transfer energy into the leading face of the impactor, and
Shustov's intuition about "well, sure, but it takes time to heat it up and
rip it apart" isn't worth much. I recall calculations when the big
Shoemaker-Levy comet -- presumed from its record of progressive break-up to
be ice-rich and "fluffier" -- hit Jupiter: they figured out the level of
thermal shock needed to disintegrate such an object, and noted casually that
it would have taken only a very few seconds longer to do the same to
nickel-iron.

So depending on the details of speed , angle of incidence, and even shape
(no reason to assume it was round except to make the math simpler), it's not
impossible for even an iron impactor to have been ripped to sparkling dust
before macroscopic chunks could hit the ground.