Hi,
In the largest scale computer simulation (by Bret Gladman) of
rocks knocked off planets, the following tables show what
percentages of chunks make it to what planets:
Ejecta From Earth/Moon
Mercury 0%
Venus 15%
Earth/Moon 50%
Mars 0.1%
Escapes 34.9%
Ejecta From Mars
Mercury 0%
Venus 4%
Earth/Moon 5%
Mars 3%
Escapes 88%
You can see that the Earth/Moon system is very good at
sweeping up its own debris (50%) while Mars only re-captures 3% of
its ejecta. The Earth (and Venus, too) get more chunks of Mars
than Mars does!
That means that, oddly enough, of the two places in the
universe that look exactly like the Mars Rover images, namely,
Mars and Arizona, you'd be better off looking for Mars meteorites
in Arizona than on Mars itself.
On the other hand, Mars gets only a tiny fraction of the Earth
rocks (one in a thousand). The Earth/Moon gets 50 times more Mars
rocks than Mars gets Earth (and Moon) rocks. So the likelihood of
finding a "terrestrial" meteorite on Mars is small indeed!
If the Earth has 25 Mars rocks (discovered), a similarly
intensive search of Earth meteorites on Mars would have been
unlikely to have found even one. Of course, meteorites may persist
on the Martian surface for much longer than they could survive on
a terrestrial surface and in that case the incidence of Earth
meteorites would be multiplied by a time factor.
If what we're looking at in the Rover images is a surface
unchanged for 3 billion years (which some would say it is), there
would be 60,000 times more Earth meteorites on it than if it
degraded meteorites as fast as the Earth does! But that's still
only one Earth (or Moon) meteorite for every 500 square miles of
Mars (scaled to the 25 Martian rocks found on Earth).
All of this assumes equal "landability" for meteorites on Mars
and the Earth, which as has been pointed out is not likely to be
the case.
Packing for Mars? It's probably a waste of time. Just put that
Universal Achondrite Detector back in the closet, hang up your
space suit, drain the fuel from your lander, and point the SUV for
Arizona instead.
Sterling K. Webb
------------------------------------
Ron Baalke wrote:
>1. Mars' thinner atmosphere means more
>meteorites survive the fall though it
>than on Earth.
There are a number of factors to consider. Mars is
smaller
than Earth, so has less gravity to pull in meteoroids.
However, Mars is closer to the asteroid belt, so is more
likely to encounter meteoroids than Earth. The thinner
atmosphere means
it is more likely a meteorite will reach the surface,
but it
also means it is more likely to impact at hypervelocity
speeds, and hypervelocity impacts tends to totally
vaporize meteorites.
Ron Baalke
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