[meteorite-list] Mars Rover's Meteorite Discovery Triggers Questions

From: Jeff Kuyken <jeff_at_meteoritecentral.com>
Date: Fri Jan 21 04:03:50 2005
Message-ID: <00db01c4ff98$1db883c0$ef2036cb_at_mandin4f89ypwu>

Howdy,

This is sort of touching on my post the other day; but if the atmosphere is
so thin and the meteor retains a lot of velocity, then I would presume the
angle of descent would not alter as significantly as it does on Earth
either! Everyone is assuming a somewhat vertical impact, but if this
meteorite hit at a 'relatively' shallow angle then it may have bounced,
ricocheted or rolled across the ground (for a considerable distance) before
coming to a stop. A shallow angle through the atmosphere may also go 'some
way' to explaining the regmaglypts with a longer burn time.

Cheers,

Jeff Kuyken
I.M.C.A. #3085
www.meteorites.com.au


----- Original Message -----
From: Matson, Robert
To: meteorite-list_at_meteoritecentral.com
Sent: Friday, January 21, 2005 5:34 AM
Subject: [meteorite-list] Mars Rover's Meteorite Discovery Triggers
Questions


Hi All,

One error I noticed in this report:

http://www.space.com/missionlaunches/mars_meteor_050120.html

> Agee pointed out that running across a meteorite on another
> planetary body would be a first. No meteorite was ever found
> on the Moon - even with all the survey work done there by both
> robots and humans, he said.

I thought two meteorites were found by Apollo astronauts -- Hadley
Rille (an EH chondrite) and Bench Crater (CM1).

I think there are two paradoxes to be solved with this fairly large
iron meteorite. The first is explaining its size in conjunction with
its apparent low level of weathering. Presumably a basketball-sized
object made of nickel-iron passing through the thin atmosphere of
Mars is going to create a crater or bury itself in a pit. How long
will it take to exhume such a meteorite under typical Mars weather
conditions? A hundred years? A thousand? Tens of thousands? And
how much weathering will take place in that time? Perhaps the first
thing to compute is the minimum impact velocity, which when coupled
with the local surface hardness should give some idea of what happened
at the time of impact. If I can find (or someone can provide) standard
atmospheric profile data for Mars, I can estimate the minimum impact
velocities and ablation percentages for preatmospheric iron meteorites
of various masses assuming grazing incidence and an initial cosmic
velocity equal to Martian escape velocity. The actual impact velocity
for the "Heat Shield Rock" will certainly be higher, but at least
we'll have a ballpark idea of the minimum impact velocity.

The second paradox is the meteorite's shape -- is the (current) Martian
atmosphere thick enough to produce the deep regmaglypting we see? My
intuition is to guess that it isn't. If today's atmosphere couldn't
do it, could the pockets have been created by a combination of atmospheric
passage and a long period of weathering? If the answer is still no,
then the iron must have fallen a very long time ago when the Martian
atmosphere was thicker. But if the atmosphere was thicker, then wouldn't
the weathering rates have been higher?

Perhaps the solution is that the meteorite fell a very long time ago
when Mars' atmosphere was thick enough to produce good regmaglpyts, but
that the ground was soft enough that the meteorite buried itself,
prolonging its lifetime by reducing the weathering rate. Eventually it
became exhumed by erosion/deflation, and whatever weathering rind it
had acquired over the millenia was quickly (in terms of geologic time)
dust-blasted away exposing bare metal in a now very dry atmosphere.

--Rob
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Received on Fri 21 Jan 2005 04:03:46 AM PST