(meteorobs) Can a meteor still be glowing when it hits Earth?

[Matson, Robert]

Hi Jack,

This may not specifically address your question, but as a non-layman I
can tell you confidently that meteors can only be "glowing" when they
hit the ground if they still retain a significant percentage of their
preatmospheric (i.e. cosmic) velocity.  And the only way this happens
is if the object in question is very large -- certainly more than a
meter in diameter.  An object that is even basketball-sized is far
too small to retain its cosmic velocity.  I tell people, somewhat
tongue-in-cheek, that if they see a glowing meteor actually hit the
ground, they are not likely to live long enough to tell anyone about
it.  ;-)

> Hi I am brand new to this site, and joined to get an answer to what
> hit our car windscreen with an huge explosion. Your layman's guess
> is based on hearsay and not an fair answer too genuine question.
> This is the type of answer I have had from professionals with PhDs.
> If something hit the planet at 90 degree how many miles of atmosphere
> and split seconds before this hits the ground.

Meteoroids that happen to intersect the earth's atmosphere head-on
(perpendicular to the ground) are very unlikely to survive atmospheric
passage.  Meteoroids that are destined to become meteorites have the
best chance if they happen to enter at shallow angles, allowing more
gradual deceleration.  As they decelerate, they will lose some 90% or
more of their initial mass to ablation, and their angle relative to
the ground will get steeper and steeper.  In a matter of only 5 to 10
seconds or so, the meteoroid will have decelerated to terminal velocity,
and will freefall the remaining distance to the ground which can take
several minutes depending on the size and density of the meteoroid.
During this period of freefall, the meteoroid is in "dark flight":
it is neither self-luminous, nor is it moving sufficiently fast to
ionize the atmosphere.

> Would this cool down?

Yes.  Think about it -- most meteoroids at earth's distance from the
sun have temperatures well below freezing.  During the very brief time
that their exteriors are heated and ablated by friction with the
earth's upper atmosphere, there is little time for that heat to
penetrate to the interior of the meteoroid.  If you heat a block of
ice with a blow torch for 10 seconds, what happens?  The outer part
melts, sure, but the interior is still ice.  The situation is analagous
with meteoroids.  Futhermore, if the meteoroid survives its fiery
passage through the mesosphere, it still has a few minutes of freefall
in which to cool off in the frigid stratosphere and troposphere.  Most
meteorites are quite cool to the touch at the time they hit the
ground.

--Rob