[meteorite-list] LEONID'S MORE HOPE FOR COLLECTORS

From: Chris Peterson <clp_at_meteoritecentral.com>
Date: Thu, 16 Nov 2006 16:14:11 -0700
Message-ID: <012101c709d4$ede2f7e0$2721500a_at_bellatrix>

Rob-

I agree that meteor showers may be able to produce meteorites. A few
showers are of asteroidal origin (the Geminids being the largest), and
cometary material may indeed be sturdy enough to make it to the ground
(something like CCs, for instance). Evidence from recent comet probes
suggests a wide range of material strengths.

One fireball I've analyzed in great depth had a parent body orbit
intriguingly similar to Comet Biela, the parent body of the Andromedids.
This is a low velocity shower which has a very broad debris stream due
to the breakup of Biela around 1846. Although no meteorites have been
recovered, the characteristics of the fireball were such that meteorite
production seems likely. The light curve suggests that the meteoroid had
a high porosity (similar to Tagish Lake).

That said, I think it's safe to say that no Leonid is ever going to make
it close to the ground. The debris stream is generally thought to
consist almost entirely of small particles, a few centimeters at most,
and we encounter it at an impressive 72 km/s. There's simply no way that
particles like that are going to fail to burn up at high altitude.

It is certain that even if meteor showers can potentially produce
meteorites, that would be a very rare event. No shower reasonably
provides an opportunity to go hunt meteorites.

Chris

*****************************************
Chris L Peterson
Cloudbait Observatory
http://www.cloudbait.com


----- Original Message -----
From: "Rob McCafferty" <rob_mccafferty at yahoo.com>
To: <Impactika at aol.com>; <meteorite-list at meteoritecentral.com>
Sent: Thursday, November 16, 2006 3:50 PM
Subject: Re: [meteorite-list] LEONID'S MORE HOPE FOR COLLECTORS


> This is going to be one of my more thoughtful and
> intellectual contributions with a serious question
>
> --- Impactika at aol.com wrote:
>
>> Sorry to disappoint you but meteor shower do not
>> produce meteorites.
>> They are minute fragments and burn completely in the
>> atmosphere.
>>
>> Too bad the Media does not know that.
>>
>
>
> Hmm. While most people with a background including
> astrophysics know this - of which I like to include
> myself as one - I have often wondered about the old
> meteorite/meteor shower conundrum
>
> I am pretty sure there are no meteorites which
> correspond date-wise to meteor showers but is this
> actually the case?
>
> While the average comet detritus is dust, it is not
> impossible, surely, for a much larger chunk to get
> ejected from a comet? The current theories of
> explosive outgassing would surely allow a chunk that
> broke off to achieve escape velocity. Is it beyond the
> realms of possibility that one of these may sit in the
> orbit of a comet waiting its transition into the
> atmosphere?
> I will confess, I have not the mathematical skill
> (primarily) nor time (secondarily) to work out the
> orbital dynamics of a big-enough chunk that broke off.
> I suspect that a large chunk is more likely to follow
> the orbital path of the main body than the dust which
> can get disperesed by radiation pressure quite
> quickly, though theres the radiative effect during
> rotation which effects orbits too (I forget its name).
> Will that cause it to move out of the comet's orbital
> path?
>
> We know comets fragment. We have photographic evidence
> of it. We know the fragments spread out (ditto). Why
> can we not have meteorites from comets?
>
> Just because we haven't yet, doesn't mean it is
> impossible. Mass extinctions have not been observed
> dur to major impact events yet, either. We all know
> that doesn't mean it can't happen or hasn't happened
> in the past. I am not sure my scenario is any
> different.
>
> That probe which crashed into the comet recently
> (again, I forget the name..I have a full time job to
> hold down), did it determine the consistency of the
> surface?
>
> Are comets and their fragments too fragile to survive
> the transition to Earth from space? If they are, then
> isn't it time we stopped likening Murchison to a
> comet?
>
> NOT SCIENTIFIC BIT.
>
> Or is it that "we just don't know?" That phrase which
> is likely to cause me to create "the dead Scientists
> Society". A secret forum where top scientists can, in
> confidence, air their misgivings and failures in
> understanding which society will not let them admit.
>
> Funny, isn't it? As society dumbs down, it expects
> the egg-heads to know and solve more! Lazy bast**ds!
>
> Rob McC
Received on Thu 16 Nov 2006 06:14:11 PM PST