Removing Pluto as a planet is abrupt psychosis

Its sufficient to say that if a planet is clearly round and orbits the
Sun
is a planet, even if its orbit mingletwines with Neptune.

new rules for a planet: "a celestial body that is in orbit around the
sun, has sufficient mass for its self-gravity to overcome rigid body
forces so that it assumes a ... nearly round shape, and has cleared the
neighborhood around its orbit."

Pluto is automatically disqualified because its oblong orbit overlaps
with Neptune's.

... well, then Neptune must not be a planet either because Pluto
intrudes into its orbit ....

Welcome to the real world.

Let me clarify the question if anybody can answer, and I doubt that
anybody is smart enough: Has Neptune cleared the neighborhood
around its orbit? Or Pluto simply does not count, because its just
a rock or something, some sort of prejudice againt dogs? Did God
appear and told astronomers: You must not think of Pluto as a
planet. You will receive 72 virgins upon altering our solar system's
planet count. Task: Convince the world that Pluto is not a planet,
and do it with a professional approach signifying your professional
confidence in the matter.

"g" == gb7648 writes:

new rules for a planet: "a celestial body that is in orbit around
the sun, has sufficient mass for its self-gravity to overcome rigid
body forces so that it assumes a ... nearly round shape, and has
cleared the neighborhood around its orbit."

Pluto is automatically disqualified because its oblong orbit
overlaps with Neptune's.

... well, then Neptune must not be a planet either because Pluto
intrudes into its orbit ....

g Let me clarify the question if anybody can answer, and I doubt that
g anybody is smart enough: Has Neptune cleared the neighborhood
g around its orbit? Or Pluto simply does not count, because its just
g a rock or something, some sort of prejudice againt dogs?

I don't recall the term "clearing the neighborhood" defined during the
IAU sessions, but I always interpreted to be a statement on the
dynamics. Neptune has cleared its neighborhood because it is the only
dynamically significant body there. There are other bodies, but their
orbits are affected by Neptune, while Neptune's orbit is not affected
by them. (The same goes for Earth and Jupiter.)

--
Lt. Lazio, HTML police | e-mail:
No means no, stop rape. | http://patriot.net/%7Ejlazio/
sci.astro FAQ at http://sciastro.astronomy.net/sci.astro.html

Let me clarify the question if anybody can answer, and I doubt that
anybody is smart enough: Has Neptune cleared the neighborhood
around its orbit? Or Pluto simply does not count, because its just
a rock or something, some sort of prejudice againt dogs?

Read
http://xxx.lanl.gov/abs/astro-ph/0608359

for two methods by which one can quantify the phrase
"cleared the neighborhood." By both metrics, Neptune did,
and Pluto didn't.

Michael Richmond

Joseph Lazio writes:

"g" == gb7648 writes:

new rules for a planet: "a celestial body that is in orbit around
the sun, has sufficient mass for its self-gravity to overcome rigid
body forces so that it assumes a ... nearly round shape, and has
cleared the neighborhood around its orbit."

Pluto is automatically disqualified because its oblong orbit
overlaps with Neptune's.

... well, then Neptune must not be a planet either because Pluto
intrudes into its orbit ....

g Let me clarify the question if anybody can answer, and I doubt that
g anybody is smart enough: Has Neptune cleared the neighborhood
g around its orbit? Or Pluto simply does not count, because its just
g a rock or something, some sort of prejudice againt dogs?

I don't recall the term "clearing the neighborhood" defined during the
IAU sessions, but I always interpreted to be a statement on the
dynamics. Neptune has cleared its neighborhood because it is the only
dynamically significant body there. There are other bodies, but their
orbits are affected by Neptune, while Neptune's orbit is not affected
by them. (The same goes for Earth and Jupiter.)

The original proposal as described in

http://www.arXiv.org/abs/astro-ph/0608359

included the qualifier that a planet is an object that has
"_substantially_" cleared its orbit, which would have allowed
for a few "stragglers" --- especially objects such as Pluto
(which is _temporarily_ in a metastable 2:3 resonance with Neptune,
from which it will in all likelihood be ejected with a lyupanov
timescale on the order of 22 million years), or the Trojans
(which are _temporarily_ in metastable 1:1 resonances with Jupiter,
and again are likely to be ejected from said resonance within
a few tens to hundreds of millions of years), or the Earth-crossing
asteroids (which are not really "in" Earth's orbit, and will
in all probability eventually be perturbed out of these orbits
and/or ejected from the solar system if they do not collide
with something first...).

Unfortunately, however, the qualifier "substantially" was dropped
from the proposal by the time it reached the floor --- albeit
there was apparently a general consensus that the definition of
"cleared its orbit" should be considered "intentionally vague,"
and that it ought to be "clarified" at some future IUA meeting... %-(

The original proposal in http://www.arXiv.org/abs/astro-ph/0608359 also
included two figures of merit that could be used to precisely quantify
what the qualifier "substantially" meant. However, despite the fact that
both criteria clearly seperated the "planets" from the "dwarf planets"
by a chasm of many orders of magnitude in either figure of merit,
apparently neither of these proposed criteria was considered "acceptable"
to The Powers That Be within the IAU, so they preferred to instead rely
on a "general understanding" of "deliberate vagueness" --- which BTW
would incidently leave the The Powers That Be within the IAU with
unlimited discretionary power over what is or isn't a "planet"
until such time as the defintion is "clarified"... %-(


-- Gordon D. Pusch

perl -e '$_ = \n"; s/NO\.//; s/SPAM\.//; print;'

In article , Gordon D.
Pusch wrote:
for a few "stragglers" --- especially objects such as Pluto
(which is _temporarily_ in a metastable 2:3 resonance with Neptune,
from which it will in all likelihood be ejected with a lyupanov
timescale on the order of 22 million years), or the Trojans
(which are _temporarily_ in metastable 1:1 resonances with Jupiter,

I'd thought that the Pluto:Neptune resonance was considered to
be stable with timescales on the order of the lifetime of the Solar
System (so far).
Do you have a reference for this claim?

--
Aidan Karley, FGS
Aberdeen, Scotland
Written at Wed, 06 Sep 2006 09:34 +0100, but posted later.

Aidan Karley .group writes:

In article , Gordon D.
Pusch wrote:
for a few "stragglers" --- especially objects such as Pluto
(which is _temporarily_ in a metastable 2:3 resonance with Neptune,
from which it will in all likelihood be ejected with a lyupanov
timescale on the order of 22 million years), or the Trojans
(which are _temporarily_ in metastable 1:1 resonances with Jupiter,

I'd thought that the Pluto:Neptune resonance was considered to
be stable with timescales on the order of the lifetime of the Solar
System (so far).
Do you have a reference for this claim?

G. J. Sussman and J. Wisdom, "Numerical evidence that the motion of Pluto
is chaotic," Science, Volume 241, pp.433--437 (22 July 1988).

Note that, since the gravitational N-body problem is Hamiltonian
(and therefore time-reversible), by the Poincare Thm there must be
just as much "phase volume" moving _into_ the vicinity of a resonance
as out of the vicinity of that resonance. Hence, to the extent that
a small body can be viewed as a "test particle" that simply "follows
the phase-space flow," it must be possible for a body to move into a
near-resonant orbit, hang close to it for on the order of a Lyapunov
timescale, and then move back out of resonance. If there are enough bodies
floating around in the vicinity of the resonance, one would expect a
near-steady-state sub-population of "transient" bodies that become
temporarily "entrained" by the resonance, and then "ejected" from it ---
and indeed, there is an observed sub-population of ~100 confirmed
"Plutinos" (KBOs near the 2:3 mean-motion resonance with Neptune),
and another hundred-odd "possible Plutinos,"

http://en.wikipedia.org/wiki/Plutino
http://www.johnstonsarchive.net/astro/tnos.html.

A number of researchers have proposed exploiting the phase-space trajectories
that approach or recede from the 1:1 "Classical Lagrange-Point" resonances
as "highways" for moving about the Solar-System with near-zero propellant
expenditure; for a popularization of this idea, see:

http://www.sciencenews.org/articles/20050416/bob9.asp.


-- Gordon D. Pusch

perl -e '$_ = \n"; s/NO\.//; s/SPAM\.//; print;'

Gordon D. Pusch wrote:
for a few "stragglers" --- especially objects such as Pluto
(which is _temporarily_ in a metastable 2:3 resonance with Neptune,
from which it will in all likelihood be ejected with a lyupanov
timescale on the order of 22 million years), or the Trojans
(which are _temporarily_ in metastable 1:1 resonances with Jupiter,

and then in a later posting gave a reference
G. J. Sussman and J. Wisdom, "Numerical evidence that the motion of Pluto
is chaotic," Science, Volume 241, pp.433--437 (22 July 1988).

Yes, solar system orbits are generally chaotic.

However, that doesn't necessarily mean that Pluto's (or any other solar
system body's) likely fate is to be *ejected* -- you can have chaos in
(say) the longitude of perihelion with only periodic changes in the
semimajor axis, and thus with the body remaining in the same general
region of the solar system.

A quick skim of Lecar, Franklin, Holman, and Murray's review paper
"Chaos in the Solar System" (ARAA 39, 581 = astro-ph/0111600) suggests
that this latter situation better describes Pluto on time scales of up
to 4 Gyr. That is, Pluto's orbit will be chaotic within a certain range
of parameter space, but Pluto won't be *ejected* from the solar system.

In contrast, most asteroids will eventually be perturbed into a planet-
crossing orbit, and thence (probably) ejected from the solar system.

ciao,

--
-- "Jonathan Thornburg -- remove -animal to reply"
Max-Planck-Institut fuer Gravitationsphysik (Albert-Einstein-Institut),
Golm, Germany, "Old Europe" http://www.aei.mpg.de/~jthorn/home.html
"Washing one's hands of the conflict between the powerful and the
powerless means to side with the powerful, not to be neutral."
-- quote by Freire / poster by Oxfam

"Jonathan Thornburg -- remove -animal to reply" writes:

Gordon D. Pusch wrote:
for a few "stragglers" --- especially objects such as Pluto
(which is _temporarily_ in a metastable 2:3 resonance with Neptune,
from which it will in all likelihood be ejected with a lyupanov
timescale on the order of 22 million years), or the Trojans
(which are _temporarily_ in metastable 1:1 resonances with Jupiter,

and then in a later posting gave a reference
G. J. Sussman and J. Wisdom, "Numerical evidence that the motion of Pluto
is chaotic," Science, Volume 241, pp.433--437 (22 July 1988).

Yes, solar system orbits are generally chaotic.

However, that doesn't necessarily mean that Pluto's (or any other solar
system body's) likely fate is to be *ejected* -- you can have chaos in
(say) the longitude of perihelion with only periodic changes in the
semimajor axis, and thus with the body remaining in the same general
region of the solar system.

A quick skim of Lecar, Franklin, Holman, and Murray's review paper
"Chaos in the Solar System" (ARAA 39, 581 = astro-ph/0111600) suggests
that this latter situation better describes Pluto on time scales of up
to 4 Gyr. That is, Pluto's orbit will be chaotic within a certain range
of parameter space, but Pluto won't be *ejected* from the solar system.

I did not mean to imply "Ejected from the Solar System" --- I meant to imply
(and wrote in the follow-up posting) that Pluto would be "Ejected from the
_2:3 RESONANCE_."

In other words, Pluto's current 2:3 mean-motion resonance with Neptune
is a _transient_ state, and it will eventually be perturbed into a
_NON-RESONANT_ orbit. The Lyapunov exponent calculated by Sussman
and Wisdom suggests that the timescale for Pluto's orbit to drift
out of resonance with Neptune is on the order of 22 million years.


-- Gordon D. Pusch

perl -e '$_ = \n"; s/NO\.//; s/SPAM\.//; print;'

[Mod. note: crucial `not' added for clarity in first sentence -- mjh]