Hi, Jeff, List,
No, my criterion was that one fall is defined as
having an origin in one meteoroid regardless of how
many fragmentation events occurred after entering
the atmosphere. This was the criterion of the MORP
study and since I wanted to compare a figure directly
with it, I tried to keep to that, i.e., Holbrook = one fall,
Pultusk = one fall.
And when your target is as small as a vehicle, it's
not hard. No cases of one car hit by two meteorites,
and no cases of multiple cars hit by the same fall. I
couldn't even unearth any account of a building hit
by multiple stones.
I discussed a number of possible target criteria:
vehicles, building, people, and gave figures for each.
The only place I wobbled was with the account of
44 people stuck in one fall in Mexico, but it turned
out to be a false report. In deriving the fall rate,
however, I decided that hits on buildings were too
likely to go undetected and that hits on people were
too incredibly rare to be useful, so I derived the fall
rate entirely from cars, all of which were cases where
there was no ambiguity.
LOUISVILLE (1977) was a fall of four recovered stones
of which only one hit a car. ST. LOUIS (1950) was a fall of
one stone that hit a car. If 40 cars had been hit in Park
Forest, it would only be one fall. For example, I omitted
counting in the target area trucks, on the grounds that
trucks are too often the target of human-propelled stones
and that trucks are large enough and noisy enough to
reduce the likelihood of hit detection, whereas a car is
usually somebody's "baby."
The only other method, I mentioned was hits on
ships, again a situation with too little data. What data
there was, was comparable to the figure derived from
cars. But a ship, larger than a truck by far, is even more
likely to be hit undetected.
The high uncertainty derives from the paucity of the
data. The 78,000 figure could be as low as 52,000 or
as high as 100,000-plus. Phil Bland's many studies
which deal with recovered falls, weathering, and dating
of individual stones, have asserted a fall rate of 48,700
per year consistently, although he expresses it as 83
per 10^6 km^2. His method also depends crucially on
the geological survival ages of meteorites on those
surfaces being studied. (Personally, I think he over-
estimates that factor in the North Africa/Sahara case,
but that's a quibble.)
http://books.google.com/books?id=N-CLZhAXQzEC&pg=PA59&lpg=PA59&dq=meteorite+fall+rate+Bland&source=bl&ots=vI-sAaoYMY&sig=_ByweAQzuF440sbasMrC20HB63c&hl=en&ei=BkzZSpqSFovg8QbHj_W2BQ&sa=X&oi=book_result&ct=result&resnum=1&ved=0CA0Q6AEwAA#v=onepage&q=meteorite%20fall%20rate%20Bland&f=false
Personally, I feel that studies from recovered falls
suffer from a crucial deficit, namely that the numbers
have been pre-filtered by an unknown factor -- that of
recovery efficiency. Until every 10 square meters of
land in an area has been scrutinized with as much
attention as people notice the appearance of their 10
square meters of automobile, recovered fall studies
will report a lower-than-the-case result.
The accuracy of the vehicle-as-target-area method
will undoubtedly increase during the century ahead,
as the number of vehicles increases, not only in the
US but around the world. I can hardly wait until China
has 150,000,000 cars! By 2109, there should be enough
hits to refine the fall rate by this method to less than
+/- 10% error.
Of course, by then we'll have so many radars in orbit
that we can count them as they come, in-bound!
Sterling K. Webb
-------------------------------------------------------------------------
----- Original Message -----
From: "Jeff Grossman" <jgross...@usgs.gov>
To: <meteorite-list@meteoritecentral.com>
Sent: Friday, October 16, 2009 10:38 PM
Subject: Re: [meteorite-list] Grimsby family shows off visitor from
space
Sterling's calculation was on 12/9/2000. I think I pointed out back
then that the calculation he did is not for the total number of falls
per year... it is the total number of stones that fall per year. At
least that is what it seems to me. I'm not sure what the average
number of stones per fall is, but it must be >10 (Holbrook alone
brings the average to over 10 even if all the other known falls had
only 1). So I'd like to challenge him to recalculate the number of
falls with this in mind.
Jeff
At 09:35 PM 10/16/2009, Sterling K. Webb wrote:
Hi, Ted, Greg, Gary, List,
Are we onto something here?
Well, yes, we are. One data point we'd really
like to have is how many meteorites fall yer year,
the annual flux. To determine it, all we have to do
is to stake out a patch of perfectly cleared planet
and recover and count all the meteorites that fall
there for several centuries or millennia.
Not so convenient, though... Since the fall of
meteorites is a random process, the total area of
the "sampling patch" does not have to be contiguous.
It can be many millions of smaller patches scattered
all over the planet. You can even move them around
randomly -- doesn't affect the accuracy of the final
calculation of the "impact cross-section of the Earth."
That "sampling patch" is CARS (and trucks, and
other vehicles). We can get a good idea of the number
of them year by year. We can closely estimate the mean
geometric cross-section of the targets. And the "lossiness"
of the experimental data is reduced by the fact that
people tend to notice when their shiny pickup truck is
holed by a meteorite!
I did all that sophisticated arithmetic ten years ago
and published a paper with the results, exclusively to
this List (which is why nobody's heard of it). The figure
widely published back them was the MORP rate of
25,530 falls per year, although Zolenski and Wells
argued in 1988 that it could be much higher:
http://adsabs.harvard.edu/full/1990amss.work...91Z
The fall rate that I calculated from this method was
approximately 78,000 falls per yesr with a possible error
of 25,000 either way. So few cars get hit. Rob Matson
chimed in that his personal estimate was a minimum
of 80,000 per annum. From that rate, I predicted (in1
Dec., 1999) that there would be at least one car hit in
the decade 2000-2009 and a better-than-50% chance
it would be two.
It seems to be two (and just in time).
That was Novemeber or December of 1999, and as we
close out 2009, Grimsby appears to be the second (Worden
in 2002 was the first). Getafe (mentioned earlier) is classed
politely as a pseudometeorite. I allowed for the increase in
the number of cars in time, based on the 1990's sales rate
increases.
.
I thought that this idea of mine was, as they say,
"methodologically sweet." I was unreasonably proud of
being so clever until I discovered this paper by Ben Hur
Wilson, entitled "A method of estimating the absolute
number of meteorites," published in 1940 in the old
POPULAR ASTRONOMY, Vol. 48 (p. 366):
http://adsabs.harvard.edu/full/1940PA.....48..366W
which contains the essence of the method. A new
idea is hard to come by.
However, Wilson based his numbers on observed falls
in specific areas which, in 1940, was scanty data. He
concluded there were 250 falls per year for the entire
planet!
Nininger disagreed violently with this; he thought
there were 500 meteorite falls per year (between 1 gram
and 1 kilogram), perhaps as many as 1,000 and cited
some of his own statistics from Kansas finds.
It seems that the more data we get, the faster they fall.
Sterling K. Webb
---------------------------------------------------------------------------
----- Original Message ----- From: "Ted Bunch" <tbe...@cableone.net>
To: "Gary Fujihara" <fuj...@mac.com>; "Greg Stanley"
<stanleygr...@hotmail.com>
Cc: <meteorite-list@meteoritecentral.com>
Sent: Friday, October 16, 2009 4:47 PM
Subject: Re: [meteorite-list] Grimsby family shows off visitor from
space
Apparently, meteorites seek out cars much like tornadoes seek out
trailer
parks. Are we onto something here?
Ted
On 10/16/09 11:31 AM, "Gary Fujihara" <fuj...@mac.com> wrote:
Wow! Another car-smashing hammer like Bendl (1938), Peekskill
(1992),
Getafe (1994)!
gary
On Oct 16, 2009, at 8:22 AM, Greg Stanley wrote:
All:
Take a look. Looks like the real deal. A hammer!
Greg S.
http://beta.stcatharinesstandard.ca/ArticleDisplay.aspx?e=2133932
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Yvonne and Tony Garchinski are the proud new owners of five
tiny meteorite fragments.
They also have a new windshield, after the space rock smashed into
their
Pathfinder three weeks ago.
"I thought it was vandalism, for sure," said Tony Friday as dozens
of reporters converged on his west Grismby home. "Who thinks a
meteorite
is going to crash-land on your car?"
The golf ball-sized fragment is likely part of a larger meteorite
that lit
up the skies of southern Ontario
Sept. 25.
The fireball was first picked up by cameras operated by the
University of
Western Ontario's physics and astronomy department 100 kilometres
above Guelph
as it streaked southeastward at a speed of about 75,000 kilometres
per hour.
Scientists released that footage Oct. 7 and began searching a
12-square-kilometre area near Grimsby
where they thought the meteor fell.
Only after seeing the footage on television did the Grimsby family
realize their car-bashing
vandal might instead be an alien invader.
"We filed a police report and everything," said a laughing Yvonne,
who held out the tiny silver and black space rock pieces for
reporters to see
Friday.
After reading up on the meteorite search, Yvonne called Phil
McCausland, an
astrophysicist at the University
of Western Ontario, who
verified the tiny rocks were out of this world.
"They're probably the oldest rocks that you or I or anyone else are
every going to hold," McCausland said. "it's pretty exciting."
The Garchinskis own the window-smashing space pebbles, but they've
agreed to
loan them to university researchers for three months.
_________________________________________________________________
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Gary Fujihara
AstroDay Institute
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(808) 640-9161, fuj...@mac.com
http://astroday.net
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Dr. Jeffrey N. Grossman phone: (703) 648-6184
US Geological Survey fax: (703) 648-6383
954 National Center
Reston, VA 20192, USA
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