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Types of meteorites
When found meteorites often have a fusion crust, then a glassy surface layer. The surface is
usually partly ablated away by the frictional heating due to passage through the atmosphere, the
fusion crust being the remains of this melted material. The heat causes a heat pulse as well as
vaporization. One can estimate the effect by seeing how much heat one gets by conversion of the
Kinetic energy to heat. The maximum encounter velocity v
max
is given by (see section on
cometary encounters):
v
max
2
= (2.41 v
0
)
2
+ v
e
2
= c. 73UP>2
= c. 73.28 km s
1
where v
0
is the Earth's orbital velocity and v
e
is the Earth's escape velocity. Most bodies actually
enter with a smaller relative velocity  around 40 km s
1
.
At v
max
the kinetic energy density is 5.2 10
9
J kg
1
. The average energy needed to melt rock is
about 1.2 10
6
J kg
1
, while the energy to crush a rock is only about 10
9
J kg
1
. The fastest ones
therefore tend not to survive. But "typical" 30 km s
1
arrivals at a low angle of entry can survive
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This note was uploaded on 12/15/2011 for the course AST AST1002 taught by Professor Emilyhoward during the Fall '10 term at Broward College.
 Fall '10
 EmilyHoward
 Astronomy, Meteorites

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