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Flight Characteristics of Meteorites


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Flight Characteristics of Meteorites,

Most people who find an unusual rock they think is a meteorite typically think it is from Mars or the Moon and worth tens of millions of dollars. There is always a fall story, usually embellished with seeing it fall from the sky with a blinding light right near them and going out and finding a new rock often burning hot or too hot to touch at the bottom of a crater. It's wishful thinking.  It is not what happens when a rock falls from space. Meteorites do not make holes, they don't burn, they don't light up from friction, and you won't see one shooting trail across the sky going all the way to the ground near you. 

Meteorites do not make holes. They land at the same speed as if you had dropped the same sized rock for a Cessna airplane. Each rock or meteorite would slow to it's terminal velocity based on air resistance. A bowling ball, or your rock, would slow to about 200 MPH. When it hit the ground it might break, or dent asphalt, but it would not make a crater. The terminal velocity of smaller stones is even lower. Galileo be damned. It would take a single stone the size of an eight passenger van to maintain enough velocity to make a crater as had occurred in Carancas, Peru, 27 Sep 2007.

Meteorites come in at hypersonic 25,000 to 40,000 MPH velocities. At just below 60 miles high the air compacts at the front of the rock by ram pressure. The air itself becomes charged and fluorescences in brilliant light immediately expanding outward from the incoming meteor along its streak, which is actually what everyone sees when they see a meteor shoot across the sky. Think about it. The typical meteor is the size of a grain of rice. You can't see that 60 miles up. I don't care how bright it is. I repeat. What you are actually seeing is the instantaneously fluorescent atmosphere created by ram pressure along the meteor's path and not the actual rock. That same ram pressure heats up the outer surface and ablates (shatters) the meteor. Most are disintegrated and go off at about to 40 miles high. The very rare bollide that could produce a strewnfield of stones on the ground will go dark at about 35 to  25 miles high. All meteors will go dark after they drop below about 4500 MPH as they will no longer be enough pressure to produce light. 

Dark flight begins in the lower atmosphere as the meteorites continue to decelerate, but now producing sonic booms. They drop subsonic below 40 to 25 miles high. The trail of stones will become quite long with larger ones traveling farther that smaller fragments. When they reach terminal velocity for that sized stone they will lose nearly all of their forward momentum and drop nearly straight down being buffeted by the jet stream and atmospheric winds.

The interior temperature of meteoriods in space is about  -250 F. In the lower atmosphere the just-heated outer surface of incoming meteorites are blasted and chilled by the -60F of ever thickening air. Just fallen meteorites are usually warm to the touch, but not too hot to touch. Sometimes larger ones are icy cold as the interior re-chills the surface. The cannot start fires, in spite of the promulgated dubious Wisconsin-Chicago fire theory. (You should read my tutorial, "How to make a landing site for a meteorite." 31 Jan 31 2019.)

Fresh meteorite falls are found on top of the ground by eyesight or by a magnet stick. Old falls containing larger stones or irons are buried much deeper and are often found by metal detectors. The reason that older fall meteorites are buried is normally not because they made a crater that deep, but that being much denser than the surrounding soil and boulders they sink slowly due to settling over the centuries. (See the depth of the Civil War bullets in my "Not Everything that Pings is a Meteorite" article 18 Dec 2018.)

Cheers!

billpeters

Edited by billpeters
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