[meteorite-list] Fall rate calculation

From: Matson, Robert <ROBERT.D.MATSON_at_meteoritecentral.com>
Date: Thu Apr 22 09:41:13 2004
Message-ID: <AF564D2B9D91D411B9FE00508BF1C8692C5F94_at_US-Torrance.mail.saic.com>

Hi All,

Kelly asked,

> Rob, when you calculate a fall rate of 160,000 per year, are you counting
> individual stones?

I was counting any paired stones as one. Let me exemplify
by using a well-known area that contributed to my overall
calculation: Lucerne Dry Lake. This dry lake has been
searched and studied extensively, dating back to the 1960s.
List member Ron Hartman is the expert on this area, having
found 4 of the 17 meteorites from this dry lake including
the first (July 1963) and the last (March 1999).

Most of these meteorites are small, and many of them are
paired (or likely paired). Grouping these, we have:

LV 001, 004, 005 (L6, S2, W3)
LV 002 (LL4)
LV 003 (H6, S3, W3)
LV 006, 008, 009, 010 (H4)
LV 007 (?)
LV 011 (L6, S4, W3)
LV 012 (H6, S2, W3)
LV 013, 014, 016 (L5, S3, W3)
LV 015 (LL6)
LV 017 (L6, S3, W4)

Pending the classification of LV 017, there are either 9 or
10 distinct falls that have been found at Lucerne Dry Lake.
The surface area of this dry lake is roughly 15 square km,
so the fall density is at least 0.6 meteorites/km^2.

If the global fall rate is 20,000 meteorites/year, the
annual fall rate per square km is .0000392. Thus, in order
to achieve a density of 0.6 meteorites/km^2, the collecting
time would need to be 15300 years. Trouble is, none of the
meteorites found are nearly that old. (Ron Hartman or Bob
Verish might be able to chime in on some of the age data,
but I believe the mean age is closer to 3000 or 4000 years.
If so, this would convert to a global annual rate of 76500
to 102000.)

I should mention that many of these meteorites are smaller
than 10 grams, so a direct comparison with Phil's numbers
is a little more difficult. Critics could also argue that
Lucerne might be a fluke -- a statistical sampling anomaly.
But preliminary results from some other areas being studied
suggest that Lucerne is not particularly unusual.

Best,
Rob
Received on Wed 28 Feb 2001 03:28:25 PM PST