[meteorite-list] Meteoroid speed (was Sikhote Alin)

From: Dieter Heinlein <dieter.heinlein_at_meteoritecentral.com>
Date: Thu Apr 22 10:31:25 2004
Message-ID: <000201c3f972$e3f0c160$dd095150_at_ba322908>

Hello list,

the region where meteoroids penetrating our atmosphere produce visible light
(so-called fireball) is mainly dominated by two factors: the air density and the
velocity of the incoming body.
Generally, "ordinary" meteoroids with preatmospheric masses in the range of
several hundred kilogramms or even several tons, entering the atmosphere at
about 20 km/s -30 km/s (72,000 km/h - 108,000 km/h) start their luminous
flight at about 90 km or 80 km height, where the Earth's atmosphere is dense
enough to interact with the incoming body.
During it's fiery flight of only several seconds the meteoroid ablates extremely
(mass loss: 90% - 99%, in most cases: 100%!) and is decelerated until the
light production stops rapidy: this is typically the case in heights of about 20 km
- 25 km, when the velocity reaches the critical value of 3 km/s (10,800 km/h).
After that point the remaining meteoroid body is decelerated even more by the
air that becomes denser at lower altitudes. After several minutes the body (then
called a meteorite) reaches the ground with the so-called free fall velocity of
about 280 km/h.

In order to produce a meteorite fall with a fireball reaching the ground, the body
must be really huge: these are the impact cratering events! The Arizona crater body
or the Noerdlinger Ries meteoroid are good examples.

I doubt very much that any of the Sikhote Alin meteorites has reached the ground
while still producing light..... because this would imply that the reach the ground
with a good portion of their cosmic velocity! Better to be VERY far away in such
a case of a meteorite fall.

Regards

Dieter Heinlein
European Fireball Network
Received on Sun 22 Feb 2004 01:10:03 PM PST