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[nathanm@MICROSOFT.com: RE: Crater Chains]

Date: Tue, 10 Sep 1996 09:59:44 -0700
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From: Nathan Myhrvold <nathanm@MICROSOFT.com>
To: mrowe@indiana.edu
Subject: RE: Crater Chains
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Sender: Nathan Myhrvold <nathanm@MICROSOFT.com>
Subject: RE: Crater Chains

There are several candidate crater chains on Earth, and more are likely
to be found.  Comet Shoemaker-Levy hitting Jupiter has caused people to

The fundamental cause of a crater chain is that the body gets within the
Roche limit, where the tidal stress of the Earth's gravity pulls it
apart.    It is also possible to fragment when it hits the upper
atmosphere, or even for a low angle impact to make multiple strikes,
either because a single body bounces like a rock skipping on a pond.
There is a spectacular set of skipping craters in South America that are
likely caused in this manner.  Yet another way to get multiple craters
is secondary impact of ejecta and fragments.

Although the Earth is less massive than Jupiter, the various effects
could still occur.  In addition, fragmentation could be caused by a
close approach to another massive body in the solar system and then
later impact Earth.

There are many sets of periodic metor showers (the Perseid, Quadrantid
and Orionid showers for example) which are due to comets which
fragmented in this manner.  Every year when the Earth passes through the
fragment cloud, we see the metors.  These are very small particles which
burn up in the atmosphere, but a similar process could occur at a larger
scale (albeit with much lower probability).