[meteorite-list] Re: Tektites IV (very short)

From: Kelly Webb <kelly_at_meteoritecentral.com>
Date: Thu Apr 22 09:43:32 2004
Message-ID: <3B551782.7AAFD2E0_at_bhil.com>

Hi, Steve and List,

    On the problems of fragmenting a large comet (10 kilometer) into
smaller enough pieces that each will airburst: The largest ice object
that will airburst is about 100 meters. A 10 kilometer comet has the
volumetric equivalent of one million such objects, so first we have the
problem of how do you break it into 1,000,000 pieces?
    Separation speeds between fragments are about 1 meter/sec. Despite
the high velocity, the low speed of separation is due to inertia. Total
flight time through the atmosphere for a large object is going to be 10
seconds or less, so the 10 kilometer comet is only going to swell into
an 11 kilometer swarm of a million objects, if it can be fragmented.
    So, another way of phrasing the question is: How many seconds will
it take to fragment a 10 kilometer comet into a million pieces? It takes
the direct physical application of force to fragment an object. Even
after a portion of the 10 kilometer comet has begun to fragment, how
much time will elapse as that force is propagated through the 10
kilometer thickness of the body? It's a question of sheer size versus
the time alotted.
     A comet travelling at 30 km/sec and coming straight in has only 3
seconds of atmospheric transit; at a low angle, perhaps 10 seconds. The
body of the comet itself is so large that if one edge were touching the
surface of the Earth at sealevel, the other edge would be higher than
Mt. Everest!
    I can see the notion of cascade fragmentation, and of course the
airbursting of the leading edge fragments would accelerate the process.
But with the density of ice (1.0 gm/cm^3), there's 200 billion tons in a
10 kilometer comet. That's a lot of material to be broken up a million
ways from Sunday in just a few seconds.

Sterling K. Webb
Received on Wed 18 Jul 2001 12:58:42 AM PDT