Excellent post, arachnophilia, filled with calm, clean, substantive answers. I trust you'll excuse one minor quibble.
it's speculation that things entering the atmosphere heat up to very very hot temperatures?
Yes. In fact, it's a myth; something that surprised me very much when I learned about it recently. The glow of a falling meteorite is not the meteor itself; but superheated air in the shock wave in front of the meteor. The immediate surface of the rock may heat up as well, but that usually melts and blows off.
The falling meteor does not get all that hot, except a bit on the surface that is lost anyway. It is not in the atmosphere long enough to pick up much heat in total.
A small meteorite will decellerate rapidly, and finally fall at terminal velocity for a few minutes before hitting the ground at a couple of hundred km/hr; during this time the surface cools again.
The main bulk of the meteor remains at the frigid temperatures of deep space, and this rapidly cools the surface. If you are lucky enough to find a meteorite just after it has fallen, it is likely to be cool, and possibly even covered with frost.
Check out
this article by Phil Plait, the Bad Astronomer, that deals with the matter in an addendum.
Sorry... I'm off topic. You guys are talking about rocks a couple of kilometers across, which have a different dynamic. They are not slowed by the atmosphere, and hit the ground at enormous velocity. That impact is what generates all the heat.
Cheers -- Sylas
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