[meteorite-list] Re: Meteorites on Mars

From: Francis Graham <francisgraham_at_meteoritecentral.com>
Date: Thu Apr 22 10:32:00 2004
Message-ID: <20040108100736.16346.qmail_at_web40112.mail.yahoo.com>

Dear List,
  I was pondering what Ron had to say about hypersonic
impacts and other comments.
  From the Wilemette, Alnighito and Hoba meteorites,
it's safe to say the largest non-hypervelocity
impactors on Earth are about ~10 meters, as an order
of magnitude.
   To avoid hypervelocity impact, the object must be
slowed by some dynamic pressure, which is proportional
to the density of the atmosphere x velocity squared.
The entry velocity is escape velocity for the planet;
For no hypervelocity impact the final velocity must be
less than the speed of sound in rock, which, in
comparison to the planet escape velocity, and for the
purposes of this crude proportionality calculation, is
close to zero.
   The escape velocity squared is proportional to g
for the planet. This is 0.4 for Mars, approximately,
compared to Earth.
   The desnity of the Mars atmosphere is about a
hundredth of Earth's, i.e., .01.
    So the max dynamic pressure available on Mars is
about 0.4 x 0.01 = ` .004 compared to Earth. So a
MASS only .004 of the largest meteorites on Earth
could be brought below hypervelocity on Mars.
    Since mass is proportional to radius cubed, the
largest meteorites on Mars to survive hypervelocity
impacts are therefore in the order of about 1 meter in
size. Since that is an approximate upper limit, we
would expect to find centimeter-size to 10 cm. size
meteorites in the Gusev strewnfield.
    Is my thinking right on this? I admit I made a
great many handwaving assumptions and used a very tiny
envelope to write on the back of. Am I in the ball
park?

Francis Graham



   
   




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Received on Thu 08 Jan 2004 05:07:36 AM PST