Ask A Scientist© Astronomy Archive

Name:    James
Status:  student
Grade:   K-3

Questiion:  Why do things "burn up" in the atmosphere?  
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The short simple answer is:  air resistance.  I assume you are referring to
"things" like meteorites and old satellites.  These have speeds of over
10,000 MPH, and when they enter the Earth's upper atmosphere, they experi-
ence frictional forces with the air molecules, which, in turn, generates
vast amounts of heat.  In everyday life we do not usually associate friction
with heat but remember the old Boy Scout (and indigenous peoples') trick of
rubbing two sticks together to make fire.

Hawley
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Up-date:  July 2008
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It is commonly believed that meteors or satellites "burn up" due to air friction or 
resistance, but it is actually caused primarily by rapid compression of air directly 
in front of the meteor particle (or satellite).
This may seem like nit-picking, but to scientists they are different processes and it's 
interesting to understand why.  Friction is formally associated with attractive 
interactions between two rubbing surfaces, like rubbing two sticks together (surprisingly, 
the common explanation that it's "unevenness" of the two materials is not accurate. Many 
very smooth surfaces have high friction, e.g., "how does teflon stick to the pan?").
It's been well documented that the nose-cone of Mach-speed (high-speed) aircraft can reach 
several hundred degrees, even though the wings and fuselage do not. If air friction were 
at play, it would heat up the entire wing as the air "rubs" over the wing's surface. But 
what we actually see is that at the nose, air is compressed directly in front of the 
aircraft and heated up from compression, just like a meteor, while the rest of the plane 
is relatively cool.  If the plane were going fast enough, it would also vaporize or "burn 
up".

Your choice of words is also interesting.  Meteors do "burn" in the sense that oxygen is 
available in the atmosphere to oxidize (burn) the meteor at those high temperatures.  I 
would expect an atmosphere of, say, pure helium, to produce different-looking meteors.

P. Bridges
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