[meteorite-list] Cold hunting?

From: Sterling K. Webb <kelly_at_meteoritecentral.com>
Date: Thu Apr 22 10:29:53 2004
Message-ID: <3F5FC3D4.6B27ECD6_at_bhil.com>

Hi, Tom,

    Taking the area of the Earth to be 5.1 x 10^8 km^2 and the
meteorite flux to be 23,930 yr^-1 (that's the figure from the MORP study), this
yields the assumed collisional cross section of the earth to be 21,360 km^2
yr^-1. This rate means that one meteorite per year falls on an area of 21,320
square kilometers.
    The inverse function of this value is how long we have to wait for a
meteorite to fall on a standard area, or the mean time to impact: 21,360 yr
km^-2. To put this flux into perspective, if you owned a house with a half-acre
yard, you would have to wait 10,552,000 years for a meteorite to fall in your
front or back yard or on your roof! (On average, that is; it could happen
tomorrow.)
    It also means that for you to find one meteorite in each square kilometer,
the one meteorite would have to survive 21,360 years (until the next one
landed!) before weathering away for there to always be one meteorite surviving
on every square kilometer.
    Of course, I think the MORP fall rate is too low and the real fall rate
could be 3-4 times higher. A meteorite could fall on every square kilometer
every 6,000 years or so. In that case, if a meteorite lasted 40,000 years and
one fell every 6,000 years, they're be five or six on every square kilometer.
    In a desert environment, this is possible as meteorites seem to last 40,000
years or so in a nice dry desert. That's if the nice dry desert stays nice and
dry for 40,000 years or more.
    The inter-mountain West of the USA was wet, with giant lakes the size of the
present Great Lakes only ten or twelve thousand years ago. (And 14,000 years
ago, there were no Great Lakes nor Mississippi River either.) The Sahara was a
wooded grassland with rivers and lakes at the same time. Even the Gobi was a
pretty nice place back then. A long-term or permanent desert is a special thing.
Chile is a good example, the Atacama has been a desert ever since they put those
Andes up... A long time ago. Another example is Namibia, or the Skeleton Coast,
as it used to be called.
    And in someplace like the US Midwest, with plentiful rainfall, frequent
floods, freezing winters and hot summers, I'd give your ordinary chondrite a
century or two at the very most before it just dissolved. That would mean
there's one surviving meteorite for every 60 to 200 square kilometers at best.
    So, if you're hunting 1.6 square kilometers in a bone-dry climate, there
should be about 10 meteorites if there's never been a flash flood or rain of any
kind for millennia. In a moderately dry climate like Arizona (which does have a
mild monsoonal rain), it's more like maybe there is one and maybe there isn't.

Sterling K. Webb
---------------------------------------------------------

Tom aka James Knudson wrote:

> Hello List, Two years ago today, Bernd pauli posted " [meteorite-list]
> Arizona Meteorite Hunters." It quoted Twink Monrad as saying;
>
> "I firmly believe that if a person were to go over any
> square mile, time after time, anywhere in the world, they'd also
> eventually find meteorites,"
>
> How many list members agree with this statement? From what I have read, I
> have always believed it. There is a one mile square field near my house that
> is pretty well left alone. I have hunted it many times, both with my hawk
> and metal detector. I have not found anything yet with the detector, but had
> plenty of success on rabbits with my hawk. If the above statement is true,
> I figure I will find something eventually, I hope. I have learned that
> hunting one square mile is not an easy task. Any suggestions on hunting a
> cold area this big? Should you use a detector?
> Thanks, Tom
> Peregrineflier <><
> The proudest member of the IMCA 6168
Received on Wed 10 Sep 2003 08:37:41 PM PDT