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From: anita@utastro.UUCP (Anita Cochran)
Newsgroups: net.astro,net.physics,net.origins
Subject: Re: Comet Origins?
Message-ID: <156@utastro.UUCP>
Date: Tue, 10-Dec-85 17:02:26 EST
Article-I.D.: utastro.156
Posted: Tue Dec 10 17:02:26 1985
Date-Received: Wed, 11-Dec-85 21:58:15 EST
References: <308@inuxm.UUCP>
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Organization: U. Texas, Astronomy, Austin, TX
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In article <308@inuxm.UUCP>, arlan@inuxm.UUCP (A Andrews) writes:
> 
> A Cable News Network interview last week showed an astronomer (astrophysicist?)
> who was saying that analysis of Halley's comet data indicates that it is entirely
> frozen water, with no (or small) other frozen components.  He went so far as to
> say that the amount of water tends to indicate that comets had to be formed much
> closer in toward the sun than the Ooo/rt cloud,and that the entire theory of cometary origins
> had to be rethought. 

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
                arpa:  anita@astro.UTEXAS.EDU  
                snail: Astronomy Dept., The Univ. of Texas, Austin, TX, 78712
                at&t:  (512) 471-1471