[meteorite-list] falls per year

From: Jeffrey N. Grossman <jgrossman_at_meteoritecentral.com>
Date: Thu Apr 22 09:41:13 2004
Message-ID: <4.3.2.7.2.20010228110816.027b91d0_at_127.0.0.1>

Each km^2 receives an average of one unique meteorite fall per 176,000
years under my calculation. However, from a practical standpoint, falls
are not unique single-point events. If the average fall spreads meteorites
across 20 km^2 (a pure guess), then it would only take 1/20 as long (9000
years) for a square km to receive a batch of recoverable meteorites. Note
that these are probabilities, and the above calculation answers a VERY
different question than you asked. To cover each and every km^2 on earth
with at least one meteorite would take much, much longer.

BTW, I repeated the Japan calculation for the densely populated regions of
northern India and northern Europe. The results are the same, more or
less, giving worldwide rates of 1860 falls/year and 3670 falls/year,
respectively, compared with the 2900/year calculated from Japan, assuming
again 30% efficiency. Again, this is recoverable falls, not recovered
fragments.

jeff

At 10:16 AM 2/28/2001, meteorites_at_space.com wrote:
>On Wed, 28 February 2001, Jeff Grossman wrote:
>
> >
> > Here's a fresh estimate of the number of RECOVERABLE meteorite falls on
> the
> > earth each year. I don't know what the other workers have done, but this
> > is a fairly simple way to get a minimum estimate:
> >
> > The most densely populated places on earth have the highest recovery rates
> > of meteorite falls. One such place is Japan. Over the last 20 years of
> > the 20th century, 10 falls were recovered there: Aomori, Tomiya,
> Kokubunji,
> > Tahara, Mihonoseki, Senboku, Neagari, Tsukuba, Kobe, and Sayama. The rate
> > was almost as high (9 meteorites) between 1920 and 1940, so this is not an
> > anomalous statistic. The surface area of Japan is 3.73e5 km^2, but
> nothing
> > is ever recovered on sparsely populated Hokkaido, so the effective area
> for
> > this calculation is 2.94e5 km^2. We can now calculate the number of falls
> > per year per km^2, and then extrapolate this to the surface of the entire
> > earth (5.12e8 km^2). Assuming my numbers are right for all these
> areas, we
> > get 870 falls/year on earth, which we can take as a lower limit on the
> true
> > value.
> >
> > This calculation assumes that the Japanese are 100% efficient at
> recovering
> > all falls in the country, which is not likely. Adding another fudge
> factor
> > for this which I'll conservatively place at 0.3 (30% efficiency), we
> get an
> > adjusted figure of 2900 falls/year on earth. If 70% of the earth is
> ocean,
> > we get a figure of 870 falls/year just on land.
> >
> > There is no object-size limit on this calculation, it's just based on
> > recoverable falls. Obviously it is biased toward bigger things.
> > Dr. Jeffrey N. Grossman phone: (703) 648-6184
> > US Geological Survey fax: (703) 648-6383
> > 954 National Center
> > Reston, VA 20192, USA
>
>
>So,
>
>What then is the flux for 1 km2 in years. That is how much time must pass
>for each km of the earth to receive one fall?
>
>Steve Schoner
>
>___________________________________________________________________
>Join the Space Program: Get FREE E-mail at http://www.space.com.

Dr. Jeffrey N. Grossman phone: (703) 648-6184
US Geological Survey fax: (703) 648-6383
954 National Center
Reston, VA 20192, USA
Received on Wed 28 Feb 2001 11:32:19 AM PST