[meteorite-list] Catching up on Met-Central

From: Matson, Robert <ROBERT.D.MATSON_at_meteoritecentral.com>
Date: Thu Apr 22 09:55:41 2004
Message-ID: <AF564D2B9D91D411B9FE00508BF1C8698E589B_at_US-Torrance.mail.saic.com>

Hi All,

Been slurping my Sunday coffee and catching up on weekend
email -- mostly posts to Meteorite Central. I wish to respond
to several posts, but I want to start with the most bizarre
one first.

I enjoy obscure humor as much as the next guy/gal, but I have
to admit that Michael Casper's latest post about his eBay
auction has me completely stumped. Either it is a very
private inside joke (which I'm supposing is lost on most
everyone here), or perhaps Michael just enjoys being
eccentric and taunting us mortals. In either case, I do
look forward to his 4-sigma posts -- their apparent randomness
(both in content and in timing) suggests extreme intelligence,
and I'm hoping that with perseverance I'll eventually "get it."

Moving on to Mohamed Yousef's posts:

> I was amazed how so many of you quickley gave me a negative
> reply.

Don't forget the likelihood of a language barrier here, folks.
Perhaps we're misreading the tone of this statement. It could
simply be high praise for our skill in so quickly identifying
a non-meteorite! ;-) (I hesitate to call it a "meteorwrong",
a term I prefer to reserve for rocks which at least superficially
resemble meteorites in one or more features.) But in all
seriousness, I would like to offer a more constructive reply.

> ... maybe I concentrated on the crystals and left out whole
> samples which looks more like what is avaialable in meteorite
> sites.

Agreed. First word of advice, Mohamed: go through all your
various samples, identify any with quartz crystals, and set
them aside. Quartz (such as what appears in the majority of
your on-line images) is a show-stopper.

> With all the negative replies I got so far, I STILL INSIST it
> is a meteorite.

Because?

> It could not be anything terrestrial.

Because?

> Although I am not an expert in the field ...

Since you freely admit this, why are you loathe to accept
the opinions of multiple independent people who are?

> ... but I am a physicist, PhD student in Cosmology ...

All well and good, but it sounds like geology and meteoritics
are not your fields of expertise. Just as there are probably
few geologists who know much about Feynman diagrams or the
Chandrasekhar limit, a physicist or cosmologist probably has
little need for understanding mineralogy or petrology.

> ... during the last few months I visited almost all sites
> about meteorites and read a few books.

We applaud your curiosity in a subject outside your primary
field(s) of interest. The more you read on the subject, the
more you will learn.

> I tried all pre-tests on these rocks and they passed.

I see a reference to magnetism on your pages, so that's
certainly an example of a good test (but mind you, not a
requirement for being a real meteorite). However, you haven't
enumerated all your tests, and clearly they are incomplete
if quartz-containing rocks are "passing".
 
> Please also try to solve with me the fossil riddle; I know
> it is not possible to have such fossils in a meteorite but
> this is what I found.

Your question is asked and answered in the same sentence.
You "know it is not possible to have such fossils in a
meteorite". It's as simple as that -- any rocks with
terrestrial fossils have been on the earth for a very
long time indeed. Few meteorites last longer than a
few tens of thousands of years in the harsh earth
environment.

Try not to be discouraged that your first candidate meteorites
are in fact terrestrial. As you learn more, you will refine
your identification criteria, and fewer and fewer candidates
will meet those criteria. With enough time, knowledge and
patience, you will find your first meteorite, and you will
probably recognize it the instant you see it.

Moving on to Robert Beauford's post, asking for help on some
questions related to fall rates:

> What proportion of visible meteors, or shooting stars, results
> in a meteorite being left on the ground? Would it be accurate
> to say far less than 1 in 10000(??)

I think that's in the ballpark. Certainly less than 1 in 2000.
Thanks to meteor showers like the Leonids, Perseids, Geminids
and so forth, most visible meteors are associated with cometary
dust and debris smaller than the size of a pea. There must be
some active meteor observers on this list -- just ask them what
fraction of their observations produced meteors brighter than
magnitude -9 (probably a reasonable lower-limit for a meteorite-
producing event). I've seen perhaps 4 in my life (one of which
back on August 31, 1984, definitely produced multiple meteorites),
versus more than 10,000 regular meteors.

> 1 object over 10 grams falls per (how many square miles) per
> year.

My best estimate, based on recoveries in California and Nevada
is around 5000 square miles. This assumes you count meteorites
from the same fall only ONCE (even though most falls produce many
individuals, each over 10 grams.) Even so, 5000 square miles is
probably an upper limit. It could quite easily be half this.

> An object over 1 kilo (2.2 lbs) might fall in a given 1 square
> mile piece of land only once in every (how many) years?

Here, there are some theoretical, exponential scaling laws you
can use to estimate comparative fall rates between stones above
10 grams and stones above 1000 grams. I'm sure it's at least
a 20:1 ratio (i.e. at least 100,000 square miles). Hopefully
someone on the list can provide more definitive data.

Cheers,
Rob
Received on Sun 06 Jan 2002 07:10:36 PM PST