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Visual Meteors Interactions

A visual meteors undergoes a series of different thermal interactions as it
penetrates the atmosphere. First, at an altitude of 80-90km the meteor begins interacting
the atmosphere.
Note, this is the same height of initial interaction of micrometeors.
In visual meteors, this intial heating is called "Pre-heating". Pre-heating brings the meteor
to a surface temperature of ~900K. At this temperature, the only loss of mass is due to fragmentation,
but as the temperature continues to rise, the surface of them meteor beings to melt.

At a temperature of ~2500K, ablation starts to occur.The mass that is stripped due to
ablation becomes hot vapor that surrounds the surface of the meteor. As the atoms in the hot vapor
excite and de-excite, they emit photons. When this begins to happen, the meteor has entered the phenomena
or "fireball" phase of interaction, as seen below.

As the fireball travels through the atmosphere, the hot vapor from ablation is compressed by collisions with
atmospheric atoms and molecules. This creates an air cap or hydrodynamic cushion that protects the meteor
from direct collisions, which can be seen in the figure below.

This barrier creates two macrostates in front of the meteor: One at 3500-5000K, which
we will call the main spectrum, and one at 10000K, which we will call the second spectrum.
For more info on the detection and differences of the two spectra: Click here

The duration of the meteor phenomena or fireball is determined by the energy contained in the mass, velocity,
temperature, etc. of the meteor. The more energy the meteor has available to it, the longer the fireball lasts.

The loss of mass due to ablation combined with the deceleration due to friction eventually slow the meteor to
a velocity where ablation is no longer occuring (assuming there is mass remaining). This period is called dark-flight.
Once dark-flight begins the meteor begins to cool very quickly. The previously molten surface solidifies as
the meteor decelerates and eventually the meteor will either collide with the Earth while decelerating or slow
to a constant velocity before it makes impact. The impact velocities are 10-100m/s for 10 g to 10 kg final masses.

We did not discuss in depth the model of the meteor's shock wave, which propagates in front of the meteor
compressing the air into a plasma, which also occurs during the fireball phase. This requires a deeper knowlegde
of ionization but can be seen in detail here.