[meteorite-list] Meteorite-list Digest, Vol 36, Issue 28

From: E.P. Grondine <epgrondine_at_meteoritecentral.com>
Date: Fri, 8 Dec 2006 08:44:06 -0800 (PST)
Message-ID: <20061208164406.59750.qmail_at_web36911.mail.mud.yahoo.com>

Hi all -

Ahah - things are becoming clearer -

Perhaps this explains to some degree the apparent lack
of cometary meteorites - their speeds are too high to
survive entry - of course, the other alternative is
that the experts in meteoritics have simply
mis-identified cometary meteorites - my guess is that
some of the iron-silicites come from cometary
nucleus's (nuclei?), but then who knows?

That's one of the things that makes meteoritics so
interesting - it's still a developing science, and a
fundamental one at that. I wonder if the term
"cuttings" will ever replace "Bessey specks" in
advertisements?

good hunting,
Ed


--- Chris Peterson <clp at alumni.caltech.edu> wrote:

> Comet Tempel-Tuttle, the parent body of the Leonids,
> is in a
> low-inclination, retrograde orbit. We encounter the
> debris at 71 km/s,
> and our own orbital speed is 29.6 km/s. Subtract
> that out and you get
> the orbital speed for Leonid meteoroids: ~41.4 km/s.
> The solar escape
> velocity at the Earth is 42.1 km/s. That's why the
> Leonids are as fast
> as any periodic meteors can be- faster meteoroids
> would leave the Solar
> System. Of course, a sporadic meteor could be
> produced by a body that
> would escape the Solar System if it didn't encounter
> the Earth- either
> because it originated outside the Solar System, or
> because it picked up
> enough energy through momentum transfer during some
> sort of slingshot
> around another body. I don't know if anybody has
> worked out the
> likelihood of that happening- very, very rare I'm
> sure.
>
> Chris
>
> *****************************************
> Chris L Peterson
> Cloudbait Observatory
> http://www.cloudbait.com
>
>
> ----- Original Message -----
> From: "Sterling K. Webb"
> <sterling_k_webb at sbcglobal.net>
> To: "Chris Peterson" <clp at alumni.caltech.edu>;
> <meteorite-list at meteoritecentral.com>
> Sent: Thursday, December 07, 2006 8:30 PM
> Subject: Re: [meteorite-list] Meteorite-list Digest,
> Vol 36, Issue 28
>
>
> > Hi, Visual, Chris, List
> >
> > For the benefit of Listees following the
> question
> > of how slow a meteoroid can be...
> >
> > The orbital velocity for any body is maximally
> > the escape velocity divided by the square root of
> 2,
> > or 70.707070707...%. Can we just call that 71%?
> > Escape velocity is 11,263.04 meters per second.
> So, the
> > highest orbital velocity is 7964.17 meters per
> second.
> >
> > That's the orbital velocity at the lowest
> possible
> > orbit, skimming over the surface. The orbital
> velocity
> > gets less and less the higher the orbit, so that
> geo-
> > synchronous orbital velocity is positively pokey,
> > around 3000 meters per second. You have to go
> faster than that just to
> > get there, then slow down
> > to stay there. Crazy stuff, that gravity.
> >
> > The only orbit that can "decay" is one close
> enough to the top of
> > the atmosphere to be slowed
> > into re-entry. But (big but), the only way an
> object
> > from somewhere "not of this earth" can get to the
> > top of our atmosphere is to fall there, in the
> course
> > of which fall, it will acquire additional
> velocity, up
> > to escape velocity.
> >
> > Escape velocity is like taxes, in that there
> just doesn't seem to
> > be any way to wiggle out.
> > By the time an object gets to the top of the
> atmosphere, it will
> > have acquired all of escape velocity except that
> which it would (try
> > to) pick up in the last 50 miles.
> >
> > By even the Earth's escape velocity of 22,263
> mps is quite slow
> > compared to the approach of most meteoroids.
> Leonids are among the
> > fastest (70,000 mps) in approach velocity (theirs
> and ours). Most
> > objects from the asteroid zone are going to
> intercept Earth at twice
> > our escape velocity or more.
> >
> > The "slow" fireball is a rarity, but the one
> most
> > likely to get something to the ground. The
> statistics
> > of meteorites (on the ground) are misleading:
> irons are much rarer
> > than their proportion on our collections. It's
> just that they can
> > withstand re-entry so much better than rocks and
> that they can persist
> > longer in an Earth environment than mere rocks do.
> In re-entry,
> > irons are better than rocks; slow rocks are better
> than fast ones; big
> > rocks are better than little ones.
> > A meteorite in the hand is better than 1000 in
> freefall.
> >
> >
> > Sterling K. Webb
>
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>
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>



 
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Received on Fri 08 Dec 2006 11:44:06 AM PST