Top 10 Ridiculously Common Science Myths
The Myth: Meteors are heated by friction when entering the atmosphere
When a meteoroid enters the atmosphere of the earth (becoming a meteor), it is actually the speed compressing the air in front of the object that causes it to heat up. It is the pressure on the air that generates a heat intense enough to make the rock so hot that is glows brilliantly for our viewing pleasure (if we are lucky enough to be looking in the sky at the right time). We should also dispel the myth about meteors being hot when they hit the earth – becoming meteorites. Meteorites are almost always cold when they hit – and in fact they are often found covered in frost. This is because they are so cold from their journey through space that the entry heat is not sufficient to do more than burn off the outer layers.
For dry air at 20°C (293 K), the speed of sound is 1125 ft/s while the rms speed of air molecules is 1647 ft/sec. Low earth orbit is ~5 miles/sec or 25,000 ft/sec. 10 miles/sec entry velocity for bolides is unremarkable. If an object hits air at 50,000 ft /sec, and 20 C is 1647 ft/sec rms, what temperature air does the object encounter? That’s a warm breeze, folks, aside from friction and compression shock.
I tried to read up on this. It’s complicated stuff, but it seems the mechanisms are different for small and large objects. A NASA engineer commented that 90% of the heating of the space shuttle was due to compression. But for micron sized meteors in the upper atmosphere, the size of hte meteor is comparable to the distance between air molecules, which makes for different ways of heating