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From: REM@MC.LCS.MIT.EDU (Robert Elton Maas)
Newsgroups: net.space
Subject: Statistics of crater counts on various moons
Message-ID: <8602100314.AA12046@s1-b.arpa>
Date: Sun, 9-Feb-86 22:14:54 EST
Article-I.D.: s1-b.8602100314.AA12046
Posted: Sun Feb  9 22:14:54 1986
Date-Received: Tue, 11-Feb-86 07:46:39 EST
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Reply-To: REM%IMSSS@SU-SCORE.ARPA
Organization: The ARPA Internet
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U> Date: 31 Jan 86 16:05:17 GMT
U> From: ucdavis!lll-crg!seismo!hao!noao!terak!mot!anasazi!will@ucbvax.berkeley.
edu  (Will Fuller)
What a horribly long USENET path!!
U> Now that we have *lots* of pretty pictures of various and
U> sundry planets and satelites throughout the solar system,
U> whats the latest and greatest in crator counting? Do the
U> statistics clearly show a variance as a function of distance
U> from the sun? Is there some sort of "hot" belt characterized
U> by heavy bombardment?

For the most part I think the variations you seek are swamped by
varying times at which the various moons solidified and started
keeping permanent record of impacts. Even icy moons like Callisto were
liquid during the very early heavy bombardment, in fact the
bombardment may have been the mechanism to keep them warm. The
heaviest bombardment was the very early time, so a slight variation in
time of solidification (a few million years one way or other) could
cause a great difference in number of craters that have occurred since
then (solid earlier -> early ones still there; solid later -> early
ones in liquid didn't stick, only few recent ones show). It's probably
not possible for a moon to be solid from day one thus keep a record of
*all* impacts since day one, thus there is probably *no* unbiased
count of impacts. However by factoring out gravitational purturbations
from parent planet and size of moon (internal radioactive decay as
well as heat retention) and other factors, it may be possible
eventually go get some idea of where the meteor swarms predominated,
but I would doubt it would be easy.

Once we land on all the moons (with robot craft presumably; those
outer moons are damn cold) and take material samples, we may be able
to radioactively date the "rocks" (water-ice, frozen ammonia, etc.)
like we did with the moon rocks, after which we'll able to time the
individual meteors and thus get a distribution in time instead of just
a gross count. At that time we'll be able to compare impact counts AT
CORRESPONDING TIMES on various moons, and test your theory.