[extropy-chat] 10th Planet Discovered

Amara Graps amara at amara.com
Wed Mar 17 17:57:59 UTC 2004


Brent Neal:
>The astronomers I've read tend to agree that one main distinction
>between small planet and Kuiper belt/Oort object is whether the core
>is uniformly solid rock, and not 'large rocky snowballs.'  Since
>NASA deepsixed the Pluto probe, so it may be a while before we know
>anything in that regard.  Pluto's orbit is certainly damning, as is
>Quaoar's and Sedna's.

Your last sentence doesn't make sense to me. The only 'damning'
thing I can see regarding Sedna's orbit is that the object seems to
come from the Oort Cloud.

No, we haven't seen the Oort cloud either, but we've experienced
closely some samples (some recent comets: Hyakutake, Hale-Bopp,
Halley, for example).

So then, continuing on this topic, why is

http://www.newscientist.com/news/news.jsp?id=ns99994780

saying :

"But orbital observations suggest it strays much further - more than
10 times its current distance - on an elliptical orbit that takes
more than 10,5000 years to complete."
[...]
"That extreme distance makes Sedna's discoverers believe it may be
the first ever sighting of an object orbiting in the remote Oort
Cloud"  ??

'First ever' sighting of an Oort Cloud object?

Hale-Bopp's orbital period is ~3000 years, Hyakutake's orbital
period is now about 14,000 years (it was ~8000 years before it
entered the inner solar system), and Halley's is a very predictable
76 years; plenty of historical observations for that one. Less
famous comets from the Oort cloud have been observed, as well.

Many (many!) years ago, Oort made his model of the Oort cloud based
on 19 comet observations ["A garden, gently raked by stellar
perturbations" he said], which had average periods of millions of
years. The comet data from the Oort Cloud has existed for a long
time.

If Sedna is an extinct comet, it can join the ranks of other extinct
comets already known in the transNeptunian region.  I don't think
astronomers would be surprised at the blurring of the comet-asteroid
distinction. And the Oort Cloud has *many* objects. It holds the most
abundant substantial bodies in the solar system: 2-5 *trillion*
comets are thought to be in the Oort Cloud.



Amara


-- 

Amara Graps, PhD
Istituto di Fisica dello Spazio Interplanetario (IFSI)
Istituto Nazionale di Astrofisica (INAF),
Adjunct Assistant Professor Astronomy, AUR,
Roma, ITALIA     Amara.Graps at ifsi.rm.cnr.it



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