[meteorite-list] Antarctic meteorite stats

From: Matson, Robert <ROBERT.D.MATSON_at_meteoritecentral.com>
Date: Thu Apr 22 10:16:31 2004
Message-ID: <AF564D2B9D91D411B9FE00508BF1C86901B4EC39_at_US-Torrance.mail.saic.com>

Hi All,

On the question of the total mass of all Antarctic meteorites,
Al commented:

> This is and would be an important consideration. I have noticed
> that a lot of the Antarctic falls are sometimes very small. Total
> mass would shed an interesting correlation to non-Antarctic finds.
> ... Also the Antarctic falls are from hundreds and thousands of
> years ago. Perhaps as much as 800,000 years ago, so there is a
> concentration of the falls on the ice sheets which may be
> distorting the numbers more.

This is part of the reason that despite the huge number of statistical
samples from Antarctica, it would be very difficult to compute an
accurate annual meteorite fall rate from them. Among the many
factors you would have to consider:

1. Movement of the ice sheets over tens of thousands of years.
Where meteorites are found today is not easily correlated to
where they actually fell. A square kilometer of a particular patch
of ice today may correspond to a quite different size and shape
for that surface in the past. You also have zones of concentration,
where large effective collection areas have been compressed into
small strips. Searching 1 km^2 of such a surface may be the
equivalent of searching 10, 100, or even a 1000 km^2.

2. Variable meteorite fall rate over the last half-million or
more years. The long lifetime of meteorites in Antarctica means
that any derived fall rate will represent an average over that
lifetime. It is likely that the flux today is different from
what it was several hundred thousand years ago. I doubt that
scientists have done terrestrial age dating on more than a tiny
fraction of Antarctic finds, so you have both the uncertainty
of the average age of all your samples and the temporal
variability in the flux rate.

3. Pairing uncertainty. Geographical location of the finds doesn't
help you much if the surface doesn't stay put. ;-) Pairing of rare
types can at least give you a good estimate of the average number of
specimens per fall (somewhere in the range of 3-6), so this ratio
can simply be applied to the common types.

With these factors in mind, has anyone attempted to estimate the annual
fall rate derived from the number of Antarctic meteorite finds?

Cheers,
Rob
Received on Fri 08 Aug 2003 09:36:18 PM PDT