arlan@inuxm.UUCP (A Andrews) (12/08/85)
*** REPLACE THIS LINE WITH YOUR MESSAGE *** 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 know Ted Holden will at once relate this to Velikovsky's Chronos theory of inundation by Saturnian discharge of water long, long ago. Are there any other ideas? (Did anyone else see this, or did I have too many Little Kings before the news that nite?) --arlan andrews (analog irregular & other things...0)
anita@utastro.UUCP (Anita Cochran) (12/11/85)
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
ugzannin@sunybcs.UUCP (Adrian Zannin) (12/12/85)
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> 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 know Ted Holden will at once relate this to Velikovsky's
> Chronos theory of inundation by Saturnian discharge of water long, long ago.
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etc.
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I am kind of new to astronomy, so could someone please explain what that cloud is and where it is? If it is accepted to be common knowledge to readers of
net, then please reply via e-mail...thanks...
--
Adrian Zannin
..{bbncca,decvax,dual,rocksvax,watmath,sbcs}!sunybcs!ugzannin
CSNET: ugzannin@Buffalo.CSNET
ARPANET: ugzannin%Buffalo@csnet-relay.ARPA
BITNET: ugzannin@sunybcs.BITNETgcb1@ukc.UUCP (G.C.Blair) (12/13/85)
> 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] replies to ......{seismo (or your link to Europe)}!mcvax!ukc!gcb1
anita@utastro.UUCP (Anita Cochran) (12/17/85)
In article <487@ukc.UUCP>, gcb1@ukc.UUCP (G.C.Blair) writes: > > 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. > Grant C Blair My statement that the comets were formed near Neptune and thrown out to the Oort cloud (for the person who asked, the Oort cloud is a halo of comets between 50 and 10000 times the distance of the earth from the Sun. There are probably a trillion comets in this region.) does not disagree with Mr. Blair's statement that the matter resides out in the Oort cloud. The time from the period of formation to the time of going out to the Oort cloud is very short (in astronomical timescales) and then the comets do indeed spend the rest of their lifetime in the Oort cloud until perturbed (although the nemesis theory does not seem to fit in with the cratering or extinction records. See articles by P. Weissman in Nature, for instance). Then, of course, the major planets are the factors which decide whether a comet is sent into the inner solar system (~10% of the time) or thrown out of the solar system. This theory, while not the only one in use today, is the one accepted by the vast majority of cometary dynamicists. They are now argueing about exact form of the Oort cloud. I am not a dynamacist but rather, I work on the chemistry of the comets and that field does offer constraints but these constraints cannot decide between formation near Neptune and out further. I am amused at Mr. Grant's dig about the "pratical" nature of our study of comets. I have attended virtually every worldwide conference on comets in the last 5 years and don't recall seeing any of his practical work. Spacecraft are indeed going to yield immense amounts of new information but their short time near the comet will afford only a one time snapshot of the comet (not to mention that the expense of spacecraft is not very pratical). Without the context of groundbased observations, these observations would not be very useful. Indeed, without the past century of ground-based observations, these spacecraft wouldn't be possible. Spectroscopic observations of comets (my research) is the best ground-based tool for probing the coma. There will be many question raised by Giotto and the other 4 spacecraft that can ONLY be answered by ground-based observations or future, much more extensive space missions such as NASA's proposed Comet Rendezvous Asteroid Flyby (CRAF) mission. -- 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
hdc@trsvax (12/27/85)
/* Written 1:18 pm Dec 17, 1985 by utastro.U!anita in trsvax:net.astro */ In article <487@ukc.UUCP>, gcb1@ukc.UUCP (G.C.Blair) writes: > I am not a dynamacist > but rather, I work on the chemistry of the comets and that field > does offer constraints but these constraints cannot decide between > formation near Neptune and out further. /* End of text from trsvax:net.astro */ But aren't those constraints pretty much supposition? The upcoming Uranus fly-by might provide a case in point. I've heard some idle talk that Uranus' hydrogen/helium ratio may be radically different than the accepted line. If so..., well suffice to say that current theorizing would have to be radically altered...?