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Date: 25 Aug 2006 07:21:48
From: Mark Smith
Subject: I'm not convinced that the new definition excludes Pluto...
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Overall, I really like the new definition of Planet, but I'm not at
all convinced that they are properly applying it. Please follow this
logic and tell me where my thinking is messed up.
First, the inner planets are where they are because two Big Bullies
(Jupiter and the Sun) forced them into position between them. They
are where they are because that is where they could survive. They are
TINY compared to the Gas Giants and if Jupiter's orbit changes, so
will the orbits of the innter planets (well, ALL other planets).
Jupter cleared it's orbit, the others simply moved to where they were
told.
Pluto is in a similar position except that it isn't sandwiched between
two big bullies. It is locked in a stable resonance with Neptune with
neither getting in each other's way. From everything I've read,
Pluto's orbit is stable AND there are no other objects that exist in
it's orbital area of influence other than Neptune. For all practical
purposes, it HAS cleared it's orbit and the only reason that orbit
isn't more circular is that there is no planet beyond it to force it
into a circular orbit. There is no reason why Pluto couldn't have
been Earth Sized and existed in this orbit.
Finally, look at the KBO's discovered so far. We haven't found many
of them, but we are assuming that the Kupier Belt will look similar to
the Asteroid Belt. There is no proof of that to date. If we were to
take a snapshot using the current definition and apply it fairly, we'd
have to say that the KBO's meet the definition. We are ASSUMING that
we'll find more objects out there that will make them more similar to
Ceres, but we have no proof. So far as we know, these bodies orbit
in a path an AU wide.
Another problem is what consititues clearing your orbit? Pretend
Saturn is a Star and we are trying to decide of it's moons are planets
by the current defintion. What do we do about the shepherd moons?
Have they cleared their orbits? They have certainly cleared out areas
in the rings. Is that good enough or would they have had to dissipate
the rings?
So the bottom line is that the definition seems to exclude Ceres, but
I'm not convinced that it excludes Pluto and the other KBO's.
And what to do about Charon? The idea of the location of the
Barycenter is intriguing. Do we need a mass differential limit as
well? What if Nix were big enough to meet the other definitions
(round, etc) but were very light. It would still orbit around a
barycenter that was outside of another body, but that would only be
because Pluto and Charon were so closely matched. Its own
contribution to the Barycenter would be negligible.
These are just musings on the definition and I'd like to seem some
considered discussion on the topic.
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Date: 25 Aug 2006 06:06:58
From: RMOLLISE
Subject: Re: I'm not convinced that the new definition excludes Pluto...
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POOR little Pluto. Lots of people seem to feel bad for him...never knew
he as so many fans. Where were all these folks when the flyby was in
trouble? ;-)
Anyhoo, it's clear and has been that the little guy has never been much
of a planet:
--Teeny-tiny...smaller than Earth's Moon.
--His orbit is pretty highly inclined to the ecliptic.
--It's pretty eccentric, too.
--Pluto is not the Planet X Lowell predicted and searched for.
--He has lots of brothers and sisters out in the Kuiper belt. Should
these be considered planets, too? "Boys and girls, the Solar System has
1247 planets at last count. Who can tell me their names?" ;-)
If you love Pluto, get out there and take a look at him. A 12-inch
scope will show him up nicely.
Peace,
Rod Mollise
Author of:
Choosing and Using a Schmidt Cassegrain Telescope
and
The Urban Astronomer's Guide
<http://skywatch.brainiac.com/astroland >
The Annual SCT User Imaging Contest is Underway!
<http://www.rothritter.com/contest/2006/ >
Mark Smith wrote:
> Overall, I really like the new definition of Planet, but I'm not at
> all convinced that they are properly applying it. Please follow this
> logic and tell me where my thinking is messed up.
>
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Date: 26 Aug 2006 03:48:31
From: Mark Smith
Subject: Re: I'm not convinced that the new definition excludes Pluto...
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>If you love Pluto, get out there and take a look at him. A 12-inch
>scope will show him up nicely.
Well, he barely shows up with my 9 1/4 if you have a good star chart.
Seriously, I think you misunderstand my argument. I took the
definition and tried to apply it to the best of my ability. I have a
hard time deciding how to define the "clearing orbit" part. If there
are many objects in Neptune Orbit Crossing 3:2 orbits as somebody else
pointed out, why do we claim that Neptune has cleared it's orbit but
these objects have not? All of the orbits are stable, right?
And what about the KBO's? The are orbiting alone in a wide swath,
correct? Haven't they either cleared their paths or forced other
objects into resonances (well, we don't know enough about them yet,
but...).
The definition isn't consistantly applied based IMO.
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Date: 27 Aug 2006 01:58:21
From: Wally Wonderful
Subject: Re: I'm not convinced that the new definition excludes Pluto...
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RMOLLISE wrote:
> POOR little Pluto. Lots of people seem to feel bad for him...never knew
> he as so many fans. Where were all these folks when the flyby was in
> trouble? ;-)
>
> Anyhoo, it's clear and has been that the little guy has never been much
> of a planet:
>
> --Teeny-tiny...smaller than Earth's Moon.
> --His orbit is pretty highly inclined to the ecliptic.
> --It's pretty eccentric, too.
> --Pluto is not the Planet X Lowell predicted and searched for.
> --He has lots of brothers and sisters out in the Kuiper belt. Should
> these be considered planets, too? "Boys and girls, the Solar System has
> 1247 planets at last count. Who can tell me their names?" ;-)
>
> If you love Pluto, get out there and take a look at him. A 12-inch
> scope will show him up nicely.
Dwarf people cant move 12" scopes! Find another solution.
>
>
> Peace,
> Rod Mollise
> Author of:
> Choosing and Using a Schmidt Cassegrain Telescope
> and
> The Urban Astronomer's Guide
> <http://skywatch.brainiac.com/astroland>
> The Annual SCT User Imaging Contest is Underway!
> <http://www.rothritter.com/contest/2006/>
>
> Mark Smith wrote:
> > Overall, I really like the new definition of Planet, but I'm not at
> > all convinced that they are properly applying it. Please follow this
> > logic and tell me where my thinking is messed up.
> >
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Date: 27 Aug 2006 01:55:14
From: Wally Wonderful
Subject: Re: I'm not convinced that the new definition excludes Pluto...
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This isnt just about Pluto, and you know it.
RMOLLISE wrote:
> POOR little Pluto. Lots of people seem to feel bad for him...never knew
> he as so many fans. Where were all these folks when the flyby was in
> trouble? ;-)
>
> Anyhoo, it's clear and has been that the little guy has never been much
> of a planet:
>
> --Teeny-tiny...smaller than Earth's Moon.
> --His orbit is pretty highly inclined to the ecliptic.
> --It's pretty eccentric, too.
> --Pluto is not the Planet X Lowell predicted and searched for.
> --He has lots of brothers and sisters out in the Kuiper belt. Should
> these be considered planets, too? "Boys and girls, the Solar System has
> 1247 planets at last count. Who can tell me their names?" ;-)
>
> If you love Pluto, get out there and take a look at him. A 12-inch
> scope will show him up nicely.
>
> Peace,
> Rod Mollise
> Author of:
> Choosing and Using a Schmidt Cassegrain Telescope
> and
> The Urban Astronomer's Guide
> <http://skywatch.brainiac.com/astroland>
> The Annual SCT User Imaging Contest is Underway!
> <http://www.rothritter.com/contest/2006/>
>
> Mark Smith wrote:
> > Overall, I really like the new definition of Planet, but I'm not at
> > all convinced that they are properly applying it. Please follow this
> > logic and tell me where my thinking is messed up.
> >
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Date: 25 Aug 2006 13:43:08
From: Per Erik Jorde
Subject: Re: I'm not convinced that the new definition excludes Pluto...
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Mark Smith <emarksmi@san.rr.com > writes:
> From everything I've read,
> Pluto's orbit is stable AND there are no other objects that exist in
> it's orbital area of influence other than Neptune.
There are many other objects in Pluto's vicinity. Approximately 25%
of all known trans-Neptunian objects share the same 3:2 resonance with
Neptuns as Pluto does and are sometimes referred to as "Plutinos"
(see http://www.ifa.hawaii.edu/~jewitt/kb/plutino.html)
> Finally, look at the KBO's discovered so far. We haven't found many
> of them, but we are assuming that the Kupier Belt will look similar to
> the Asteroid Belt.
Actually, more than 1000 are now known.
> So far as we know, these bodies orbit
> in a path an AU wide.
No, the zone is _much_ wider than 1 AU. If you include the so-called
scattered disc objects (SCO, such as e.g. 2003 UB313) they extent at
least out to 100 AU (and perhaps to several 100s AU). Even classical
Kuiper belt objects (or "cubewanos", after 1992 QB1) cover a belt
several AUs wide (most having semimajor axis between 42 and 48 AU).
pej
--
Per Erik Jorde
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Date: 25 Aug 2006 15:56:53
From: SkySea
Subject: Re: I'm not convinced that the new definition excludes Pluto...
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>Per Erik Jorde <perik@pulsar.imr.no> wrote:
>There are many other objects in Pluto's vicinity. Approximately 25%
>of all known trans-Neptunian objects share the same 3:2 resonance with
>Neptuns as Pluto does and are sometimes referred to as "Plutinos"
>(see http://www.ifa.hawaii.edu/~jewitt/kb/plutino.html)
Hmm... Perhaps the definitions of "planetary system" and "orbit"
should be re-examined.
If Pluto and several other KBOs have orbits influenced by Neptune (I
assume, rather than Neptune's orbit having been influenced into
resonance by the KBOs), then perhaps these orbits should be considered
as around Neptune. It's not a classical orbit (centered around a
massive body), but it seems that these are all part of a single
system.
That of course, would mean Pluto is a moon of Neptune.
It would also address the issue of the Trojan asteroids. They would be
moons of Jupiter, as Jupiter is the determining factor for the
location of the stable points in its track.
Ceres would be a planet, if we wanted to continue the
roundness/independent-orbit definition. But there are (probably)
scores of oblate spheroid KBOs in their own, unlocked, stable orbits
(around the Sun).
=============
- Dale Gombert (SkySea at aol.com)
122.38W, 47.58N, W. Seattle, WA
http://flavorj.com/~skysea
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Date: 25 Aug 2006 09:24:08
From: Brian Tung
Subject: Re: I'm not convinced that the new definition excludes Pluto...
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SkySea wrote:
> If Pluto and several other KBOs have orbits influenced by Neptune (I
> assume, rather than Neptune's orbit having been influenced into
> resonance by the KBOs), then perhaps these orbits should be considered
> as around Neptune. It's not a classical orbit (centered around a
> massive body), but it seems that these are all part of a single
> system.
That would only make sense if the resonance were 1:1. I don't think
that's very likely for an object not in one of the stable Lagrange
points (L4 or L5). I'm pretty sure that such an object would get
ejected if it weren't massive enough, and if it were massive enough, it
would probably do something like the event that created our Moon.
I think intuitively, we think of a satellite as an object that is always
near the parent planet, not something that could, at times, be all the
way on the other side of the Sun.
--
Brian Tung <brian@isi.edu >
The Astronomy Corner at http://astro.isi.edu/
Unofficial C5+ Home Page at http://astro.isi.edu/c5plus/
The PleiadAtlas Home Page at http://astro.isi.edu/pleiadatlas/
My Own Personal FAQ (SAA) at http://astro.isi.edu/reference/faq.html
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Date: 25 Aug 2006 18:47:25
From: SkySea
Subject: Re: I'm not convinced that the new definition excludes Pluto...
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>brian@isi.edu (Brian Tung) wrote:
>That would only make sense if the resonance were 1:1. I don't think
>that's very likely for an object not in one of the stable Lagrange
>points (L4 or L5). I'm pretty sure that such an object would get
>ejected if it weren't massive enough, and if it were massive enough, it
>would probably do something like the event that created our Moon.
I don't understand why it would it only make sense for a 1:1
resonance, given there's an interaction in the case of Neptune and
Pluto that maintains the orbits as they are. The orbital ratios are
not 1:1. The trojans' location are maintained by the presence of
Jupiter. Pluto is more vulnerable to being grabbed away, because it is
more often out of Neptune's direct influnce. But the mechanism and
outcome is the same: the large planets maintain the orbits of their
subordinates. It's a system.
>I think intuitively, we think of a satellite as an object that is always
>near the parent planet, not something that could, at times, be all the
>way on the other side of the Sun.
That's exactly my point and question: Is it reasonable to consider
orbiting systems as involving more than the classical idea of one
object running circles around another? I concede that "orbit" is the
wrong term. But the interaction exists, maintains the system as it is,
and therefore nomenclature should at least provide for expanding the
concept of "system". A "flock" of planets (Neptune "shepherding"
Pluto, ala Saturn's shepherd moons)? Instead of moons, "sheep"?
(okay, silly...)
But the terminology is not my point. The concepts of systems involving
entire rings or bands of orbits, and consideration of those entire
systems when defining what a "planet" would be my point.
=============
- Dale Gombert (SkySea at aol.com)
122.38W, 47.58N, W. Seattle, WA
http://flavorj.com/~skysea
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Date: 25 Aug 2006 14:49:53
From: Brian Tung
Subject: Re: I'm not convinced that the new definition excludes Pluto...
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SkySea wrote:
> I don't understand why it would it only make sense for a 1:1
> resonance, given there's an interaction in the case of Neptune and
> Pluto that maintains the orbits as they are.
Yes, but Pluto doesn't satisfy anyone's intuition (except maybe yours)
about what a satellite should do. The term was chosen because it means
"attendant," and attendants are generally around the thing they attend
to. Not all the way on the other side of the world, or in this case,
the solar system.
If Pluto were in L1 or L2 with Neptune, and somehow managed to stay
there, it would be in a kind of 1:1 resonance with Neptune, and would
stay close to Neptune all the time, and I could see calling it a
satellite, even though it would not actually be orbiting Neptune from
a Neptunocentric perspective. (It would make one orbit per Neptunian
year from a sidereal perspective, of course.) It was in that sense
that I meant that only a 1:1 resonance would make sense for the term
"satellite."
Another property of satellites that is not even satisfied by an L1 or
L2 object is that we can consider them and the parent body as an
isolated system, to a first order approximation. We can then treat
that system as a single body in orbit around the Sun, to a first order
approximation. That is why it makes sense to call such objects
different names from the ones we use for major planets--because we
study them differently. No one computes Triton's position independently
of Neptune's for instance; we compute Neptune's position, and then
figure out Triton's from there. Pluto's position, on the other hand,
is computed independently of Neptune's. That is only one reason why I
think it doesn't make sense to think of them in any kind of major-minor
relationship.
> That's exactly my point and question: Is it reasonable to consider
> orbiting systems as involving more than the classical idea of one
> object running circles around another? I concede that "orbit" is the
> wrong term. But the interaction exists, maintains the system as it is,
> and therefore nomenclature should at least provide for expanding the
> concept of "system". A "flock" of planets (Neptune "shepherding"
> Pluto, ala Saturn's shepherd moons)? Instead of moons, "sheep"?
> (okay, silly...)
I think the proper way to say that is, "Neptune and Pluto are in a
3:2 resonance relationship." That's pretty succinct, and I don't see
any benefit in making any kind of hierarchical structure out of it, or
adding any nomenclature to represent that.
Remember, the resonance thing works over extremely long time periods.
Even Pluto's orbit can be figured out from Kepler's laws to a decent
first approximation. Not good enough to find it in a scope, mind you,
but conceptually, it's still an ellipse with the Sun roughly at one of
the foci. Only over periods of at least tens, probably hundreds of
orbits, does the resonance begin to make a significant contribution.
> But the terminology is not my point. The concepts of systems involving
> entire rings or bands of orbits, and consideration of those entire
> systems when defining what a "planet" would be my point.
OK. I don't find such considerations compelling in the case of Neptune
and Pluto, though.
--
Brian Tung <brian@isi.edu >
The Astronomy Corner at http://astro.isi.edu/
Unofficial C5+ Home Page at http://astro.isi.edu/c5plus/
The PleiadAtlas Home Page at http://astro.isi.edu/pleiadatlas/
My Own Personal FAQ (SAA) at http://astro.isi.edu/reference/faq.html
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Date: 26 Aug 2006 03:54:16
From: Mark Smith
Subject: Re: I'm not convinced that the new definition excludes Pluto...
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>> So far as we know, these bodies orbit
>> in a path an AU wide.
>
>No, the zone is _much_ wider than 1 AU. If you include the so-called
>scattered disc objects (SCO, such as e.g. 2003 UB313) they extent at
>least out to 100 AU (and perhaps to several 100s AU). Even classical
>Kuiper belt objects (or "cubewanos", after 1992 QB1) cover a belt
>several AUs wide (most having semimajor axis between 42 and 48 AU).
Sorry, I misspoke. I meant that no other object every comes within an
AU of the body in question.
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