[meteorite-list] Meteorite Questions

From: Rob McCafferty <rob_mccafferty_at_meteoritecentral.com>
Date: Wed, 29 Aug 2007 17:00:29 -0700 (PDT)
Message-ID: <234818.60702.qm_at_web51005.mail.re2.yahoo.com>

Meteor Crater is pretty much square. I believe
weathering has a lot to do with it. Even a desert gets
a fair bit of rain in 50,000 years.
I think I read that the original crater has been half
filled with weathered material though why it would be
square following this is anyones guess. Why not (?) ,
I suppose. Prevailing winds and stuff, maybe.

Yes Tatahouine is a rather fetching green. I never
questioned why, when my other diogenite slice look
yellow. I put it down to slice vs stone and a general
variability of rock. Maybe it's a special case. I have
a chunk of NWA1877 (olivine diogenite) and thats not
green at all. Again, yellow...with browny bits.

Diogenites are made from hypersthene (an
orthopyroxene) not olivine. This doesn't answer why
some are green and others are yellow, though.

Only terrestrial olivine tends to look
green(Encyclopaedia of Meteorites). The crystals in
pallasites are olivine but they're yellow to black.
Maybe there's a green one. I suspect there may be but
don't know of it.

Definition Meteoroid: A solid object moving in
interplanetary space, of a size considerably smaller
than a asteroid and considerably larger than an atom
or molecule
www.space.com/spacewatch/meteor_forecast.html

Since they're all likely to be of similar size,
usually from a comet, they are effected in the same
way by all the different forces. (gravitational
pertubations, sunlight which pushes them out, that
"wierd thing" - where they move inward due to rotation
and some quantum effect which has a name which is
wierd to someone who speaks english but I suspect is
something italian, probably the blokes name- , and
time.

Meteor showers, of course come from these groups but
they occur every year rather than just when the comet
is here because of the spreading out you mentioned
with SL9. When they break off from the main body some
go in and some go out but not far enough to form
discrete orbits, they stay with the pack, so-to-speak.
the ones on the inside track orbit faster than the
ones on the outside track so the particles eventually
become spread out over the entire cometary orbit. Why
the perseids have a 33year peak, where a load of stuff
seems to be clumped together , I don't know.

Speaking of I don't know, I will leave the rest for
that reason.

Ciao

Rob McC



--- Walter Branch <waltbranch at bellsouth.net> wrote:

> Hello Everyone,
>
> I have had plenty of time recently to ponder things
> such as meteorites. I
> am also alone at home at present and am bored.
> Would some kind,
> more-knowledgeable-than-me soul help me with some
> meteoritical questions.
>
> For example, why does the rim of meteor crater
> appear "squared" in some
> photos, while in others it appears very round?
> Perspective? Lighting?
> Extremely highly localized tectonic shifting (back
> and forth)?
>
> Also, why is Tatahouine so green? Olivine? Krylon?
>
> I am looking at a slice of NWA 4664 right now (thank
> you Eric Olson) and I
> don't see any much green. Maybe that one is a bad
> example because NWA 4664
> doesn't even look like at Diogenite!
>
> Also, I have read that some meteoroids travel
> through space in streams and
> impact the Earth simultaneously (i.e., they have
> already broken up before
> they hit the Earth's atmosphere). How can this be?
> I would think that once
> a meteoroid has broken in space (most likely due to
> impact), minute
> deviations of the individual pieces in the initial
> trajectory would
> translate into ever increasing deviations in the
> individual piece's
> trajectory, over time. Unless two pieces were
> traveling in EXACTLY parallel
> lines, over time the pieces would be widely
> dispersed in space.
>
> Remember comet Shoemaker-Levy 9? It was broken
> apart by gravitational
> forces from Jupiter only a year prior to impact, yet
> by the time it had
> encountered the Jovian atmosphere the separation
> between the pieces was
> wider than the diameter of the Earth! After only a
> year.
>
> Traveling over eons to make it to the inner solar
> system, how can a
> meteoroid stream stay intact enough to cause a tiny
> strewnfield on the
> Earth? I would not think that the Earth's
> gravitational field would be
> strong enough to do what Jupiter did.
>
> Also, I know I have asked this before but I still
> don't understand how
> researchers can determine cosmic ray exposure ages
> for a meteorite which
> ablated a significant portion of the material that
> absorbed most of the
> cosmic rays and which may have fragmented in flight
> through the Earth's
> atmosphere.
>
> Anyone?
>
> -Walter Branch
> ________________________
>
>
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>



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Received on Wed 29 Aug 2007 08:00:29 PM PDT