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From: gcb1@ukc.UUCP (G.C.Blair)
Newsgroups: net.astro,net.physics,net.origins
Subject: Re: Comet Origins?
Message-ID: <487@ukc.UUCP>
Date: Fri, 13-Dec-85 06:36:39 EST
Article-I.D.: ukc.487
Posted: Fri Dec 13 06:36:39 1985
Date-Received: Mon, 16-Dec-85 04:50:22 EST
References: <308@inuxm.UUCP> <156@utastro.UUCP>
Organization: U of Kent at Canterbury, Canterbury, UK
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Xref: watmath net.astro:1188 net.physics:3688 net.origins:2725

> I am an astronomer who makes my living studying comets.  The evidence to date
> indicates that comets are dominated by water ice but other ices exist in
> siginificant amounts.  The present theory is that the comets formed somewhere
> near Neptune and were thrown out to the Oort cloud.  This is a dynamical
> arguement not based on the chemical composition, per se.  The theory
> of cometary origins is not changed by Halley.  Indeed, Halley is quite
> an ordinary comet.  It is still most likely that comets formed with
> the initial formation of the solar system and they are composed of
> ices reminiscent of the early solar nebula.
> -- 
>  Anita Cochran  uucp:  {noao, ut-sally, ut-ngp}!utastro!anita
Here at the University of Kent at Canterbury, England, we pride ourselves
in being at the forefront of *practical* cometary research, with a large
involvement in the European Space Agency's Giotto Mission. I tend to not
agree with Anita when she refers to comets being formed somewhere near
Neptune & then thrown out to the Oort cloud. My own (personal) view is
that the cometary matter usually resides out at the Oort cloud radius,
and that once in a while, it is perturbed by passing bodies (Nemesis?)
and further perturbed by the major planets, causing the occasional comet
to be seen within the inner Solar System. As to the compostion, I think
it's mainly along the lines expressed by Anita, but the only way of
knowing is when Giotto hurtles toward the nucleus on March 13th 1986,
hopefully sending back something useful before obliteration.
I would add though that I predict that the amount of non-icelike solid
material in the nuclear region is probably higher than many people think.

		Grant C Blair

University of Kent at Canterbury Unit for Space Sciences
[Views expressed in this document are not necessarily held by the entire Unit]

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