PDA

View Full Version : Pluto as largest Trans-Neptunian Object (TNO)



ljbrs
2001-Dec-29, 12:47 AM
What are your thoughts about this. Are you in favor of categorizing celestial objects according to their physical characteristics, or would you rather keep everything just the way it is -- no change.

If Pluto is not actually a planet (in that it has characteristics strongly similar to Trans-Neptunian Objects (TNOs) but no physical characteristics which would be scientifically comparable to the planets in the Solar System, or even to the Solar System moons, should the scientifically correct answer be to place it in its actual category along with other similar objects in the Solar System, rather than force it into a category where it does not physically belong (such as planets)?

Now, be reasonable about this, because it looks as if Pluto (and Charon) will be considered as planet and moon, as well as being designated the largest TNOs in the Kuiper Belt.

ljbrs /phpBB/images/smiles/icon_biggrin.gif /phpBB/images/smiles/icon_smile.gif /phpBB/images/smiles/icon_wink.gif /phpBB/images/smiles/icon_frown.gif

GrapesOfWrath
2001-Dec-29, 11:54 AM
Here is the criteria I posted to the old BABB, for consideration:

A planet is a body that meets the
following criteria:
1) It is not a star or brown dwarf
2) Primary gravitational influence is a star or brown dwarf
3) It is approximately spherical
4) Center of gravity of two-body system is not inside another planet
5) Larger than 200km radius

Number 3 is still vague, but we could decide on an actual parameter, excluding effects of rotation of course.

ljbrs
2001-Dec-29, 04:47 PM
I will follow the thinking of Brian Marsden and the International Astronomical Union (IAU).

Pluto does not have a consistent orbit with relation to the other planets in the Solar System. It is not made of material consistent with any of the planets in the Solar System. Its orbit and its composition are very similar to the other Trans-Neptunian Objects (TNOs).

Perhaps you have made up your ideas on this matter. Perhaps the astronomers with the IAU have their ideas. I go with their thinking, because they are selected from the best of the international astronomers. It is their job to make such distinctions. I have trust in them.

Some of our asteroids are spherical. Does this also make them planets or minor planets? They orbit the Sun in the Asteroid Belt, many of them in a consistent motion to the other planets in the Solar System. Pluto orbits the Sun in the outskirts of the Kuiper Belt. Does this make objects in the Kuiper Belt which are spherical out to be true planets? Designations are simply made in order to distinguish objects as to their characteristics. You left out of your list several characteristics which would be different for Pluto with respect to the other planets in the Solar System. Pluto's orbit is much different and Pluto does not seem to have developed in the same manner as the other planets. Pluto's (and Charon's) composition is much different.

I simply thought that this subject would be a good one for people who are interested in astronomy of the Solar System. I respect Brian Marsden and the other members of the IAU and will go with their decisions.

ljbrs /phpBB/images/smiles/icon_rolleyes.gif /phpBB/images/smiles/icon_wink.gif /phpBB/images/smiles/icon_rolleyes.gif

Kaptain K
2001-Dec-29, 05:57 PM
Last I heard, Brian Marsden's position was that Pluto should have a dual classification. A planet - since that is it's established classification. First and (so far) largest TNO.
I have no problem with this.

ljbrs
2001-Dec-29, 08:15 PM
Last I heard, Brian Marsden's position was that Pluto should have a dual classification. A planet - since that is it's established classification. First and (so far) largest TNO.
I have no problem with this.
_________________
TANSTAAFL!


That is exactly right! I do not expect that Pluto will ever be completely demoted. Originally, the IAU was going to switch Pluto's category to Trans-Neptunian Object, but changed its mind when the public uproar became deafening. Also, Clyde Tombaugh was still alive at the time of this proposed status reevaluation, and everybody backed off, perhaps out of deference to him, perhaps out of their respect for the public's (and astronomers') dislike of change (after having memorized the nine planets in their childhood).

Anyway, I think that the decision of the IAU to accept both categories makes study of the object, both as a Trans-Neptunian Object (TNO), and as our ninth planet, a much better decision. I think that the dual category is the best solution, keeping everybody happy.

Now, let us hope that there will be a mission to Pluto (and beyond) to study this difficult, and enticing, object.

ljbrs /phpBB/images/smiles/icon_biggrin.gif /phpBB/images/smiles/icon_smile.gif /phpBB/images/smiles/icon_wink.gif

_________________
*Nothing is more damaging to a new truth than an old error.* Goethe

<font size=-1>[ This Message was edited by: ljbrs on 2001-12-29 15:18 ]</font>

bup
2001-Dec-29, 10:51 PM
I think TNO is the worst form of compromise. It is a compromise simply to be one. It's not a good category of 'space thing.'

As we learn more about other star systems, we will certainly find more planets. There are almost certainly other moons. There are probably comets and asteroids, and something like a Kuiper Belt and Oort Cloud around most other systems.

Nowhere else in the universe will there be other trans-Neptunian objects, because nowhere else is a planet named Neptune. Even if we change it to 'planetoids that have orbits partly inside the outermost planet,' what's the point? It's a pretty unimportant property to make a whole category out of it.

The distinction between planet and planetoid is gray - in nature, not just in astronomers' arguments. I have no problem with the decision to keep it as planet, since it was arbitrarily designated as such originally.

ljbrs
2001-Dec-31, 01:52 AM
I think TNO is the worst form of compromise. It is a compromise simply to be one. It's not a good category of 'space thing.'

As we learn more about other star systems, we will certainly find more planets. There are almost certainly other moons. There are probably comets and asteroids, and something like a Kuiper Belt and Oort Cloud around most other systems.

Nowhere else in the universe will there be other trans-Neptunian objects, because nowhere else is a planet named Neptune. Even if we change it to 'planetoids that have orbits partly inside the outermost planet,' what's the point? It's a pretty unimportant property to make a whole category out of it.

The distinction between planet and planetoid is gray - in nature, not just in astronomers' arguments. I have no problem with the decision to keep it as planet, since it was arbitrarily designated as such originally.


TNO is not a compromise. Pluto (and Charon) are more like the objects in the Kuiper Belt than like the objects one designates as planets. For one thing, Pluto's orbit seems to coincide with the TNOs and not at all with the planets. Pluto's composition is icy, which is more like Kuiper Belt objects. If scientists must give up carefully studied characteristics to differentiate objects, then there can be no categories at all. The defining categories are not for the casual observer of astronomy; they are for the professional astronomers themselves. Without categories, classification in astronomy would result in chaos. For instance, it would be foolish to categorize a black dwarf star (the final stage of a white dwarf star) as a black hole simply because neither black dwarf stars nor black holes can be easily observed. The black hole would be defined as having only three characteristics: Mass, charge, and spin. The same could not be part of the definition of a black dwarf star whose only similarity would be a difficulty in its being seen.

Pluto's and Charon's icy compositions and their odd orbit (not like any of the other Solar System planets) make it unusual. However, Pluto has a great similarity to the Kuiper Belt Objects. The Astronomers are simply giving in to majority rule (as far as the public is concerned) in permitting both categories. However, in order to study objects with Kuiper Belt characteristics, they need to include Pluto and Charon in that category for the purpose of science. The ordinary person need not become bothered about the details. Since Pluto and Charon will continue to be a planet/moon pair, why should the public care about technicalities? The public gets their classification and the Kuiper Belt astronomers will get their combined classification. Never the twain should need to meet. Categorization is found in science. Those who are not scientists, including myself, should not bother their heads about the nomenclature.

I, personally, have no problem with it. Changes in science have never bothered me. I always love it when a theory is reformulated because of revisions due to observation. Science is exciting because it changes.

Pluto and Charon are going to continue to be classified as a planet and moon. I do not see the problem at all.

ljbrs /phpBB/images/smiles/icon_smile.gif

Lorenzo
2001-Dec-31, 10:30 AM
Frankly speaking, I do think that Pluto should be classified as a TNO
object only. The "dual" nature seems something of mystical to me... /phpBB/images/smiles/icon_biggrin.gif

If this has not happened (so far), it is because Pluto is the only "planet"
discovered by an American astronomer in the USA . From the human point of view,
it is understandable that people in the USA are reluctant to "remove" Pluto from
its previous status, so the compromise is acceptable, for one or two
generations.

The question is: what are teachers really teaching in the schools about the
solar system? What about astronomy books and astronomy media? Are they
accurately following the IAU recommendations or are they following the "ordinary
people spirit"?

Probably in 2102 (I will always be in the memberlist of BABB, and you?) nobody
will remember that Pluto was once considered a planet, also because in the
meantime many important objects will be discovered in the Kuiper Belt, and even
beyond!

GrapesOfWrath
2001-Dec-31, 02:31 PM
On 2001-12-29 12:57, Kaptain K wrote:
Last I heard, Brian Marsden's position was that Pluto should have a dual classification. A planet - since that is it's established classification. First and (so far) largest TNO.
This Sky and Telescope article (http://www.skypub.com/sights/moonplanets/9905pluto.html) says that Marsden, director of the Minor Planet Center, has been trying to demote Pluto for over twenty years, without success. He justifies the reclassification because it "might eliminate its inadvertent rediscovery by observers who occasionally mistake it for a faint new object." Anybody who "forgets" about Pluto is a little careless, don't you think?

Accusing the other side of personal motives is unfair. That opens up a can of worms--both sides are susceptible, and it's unfair. For instance, is Brian Marsden trying to "take over" Pluto, as director of the Center? What was his response when it was suggested that Pluto be classified as trans-Newtonian object TN/1? He opposed the creation of a new classification system--which doesn't seem to fit with the explanation that we are trying to categorize these objects appropriately. TNOs are as like the objects of the asteroid belt as they are planets.

I suggested those criteria for planets for consideration because we don't have any. As the Sky and Telescope article mentions, Pluto satisfies almost any criteria for planethood. Is there anything wrong with the criteria I mentioned? Would Ceres really be considered a planet also?

There are a few asteroids that satisfy all criteria, except #3. 1 Ceres (http://cfa-www.harvard.edu/~jhora/mirac/ceres.html) seems distinctly football shaped (though that Sky and Telescope article, in its last paragraph, seems to say otherwise), 4 Vesta (http://oposite.stsci.edu/ftp/pubinfo/jpeg/Vesta24.jpg) has a noticeable non-sphericity, and although I didn't find a photo of 2 Pallas (http://nssdc.gsfc.nasa.gov/planetary/factsheet/asteroidfact.html), its dimensions are listed as 570 x 525 x 482km. 10 Hygiea (http://seds.lpl.arizona.edu/billa/tnp/asteroids.html) has a radius of 215, but I didn't find any axial information -- so it might be a planet under this definition, but I doubt it. Those are the only asteroids with a radius greater than 200km.

TNO Varuna (http://www.ifa.hawaii.edu/faculty/jewitt/varuna.html) may have a radius of about 450km, but other TNOs discovered appear to be around 200km or less. I only really added rule 5 to make sure very small objects weren't considered--otherwise, a baseball thrown out the window of a planetary probe would satisfy all the other criteria!
_________________
rocks

<font size=-1>[Fixed format, added comment on rule 5]</font>

<font size=-1>[ This Message was edited by: GrapesOfWrath on 2001-12-31 09:37 ]</font>

bup
2001-Dec-31, 02:58 PM
On 2001-12-30 20:52, ljbrs wrote:

TNO is not a compromise. Pluto (and Charon) are more like the objects in the Kuiper Belt than like the objects one designates as planets. For one thing, Pluto's orbit seems to coincide with the TNOs and not at all with the planets. Pluto's composition is icy, which is more like Kuiper Belt objects.


Well, then, I could live with it being designated a Kuiper belt object. Trans-Neptunian object is simply a bad term. IIRC, the term 'TNO' was introduced to create a new category for Pluto, and not as another name for Kuiper Belt objects.

In truth, I think, career astronomers already consider Pluto the largest known Kuiper belt object. The public at large considers it a planet. That's the way I think it's going to stay.

David Hall
2001-Dec-31, 02:59 PM
As for myself, I think it's quite probable that we may decide to demote Pluto eventually. But for now I say we should keep the current standings. I think there's just not enough data to be sure whether Pluto can be considered a TNO or not, because we don't know enough about either Pluto or TNO's to be able to compare them accurately.

What we really need is a mission out there to find out what Pluto really is like. More sightings of TNO's and their make-up would help. If we discover a few more very large TNO's and also find that Pluto is basically identical to them, then there'll be more of a basis for a demotion.

It would also help if we had a clear-cut definition of a planet, such as the one given above. But also, should composition be a factor? Is similarity (or lack thereof) to other known objects really a factor in determining planethood?

At this time there's no difficulty that I can see with keeping planetary status and at the same time studying Pluto as if it were a TNO. When we know more, we can make more clear-cut decisions. What concerns me more is why there's so much trouble getting a mission out there to begin with. It takes so long to get something out there that we have to get cracking. Let's hurry up and get a probe on it's way!


PS:

<font size=+2>***Happy New Year to everyone!***</font>

(It's 01:30am Jan. 1, 2002 where I am, so I can be the first to say so! /phpBB/images/smiles/icon_biggrin.gif /phpBB/images/smiles/icon_biggrin.gif)

Kaptain K
2001-Dec-31, 03:32 PM
Unfortunately, NASA hemmed and hawed and missed the last window to launch a mission that could get there before the atmosphere freezes out.

GrapesOfWrath
2001-Dec-31, 03:52 PM
From the OP:


If Pluto is not actually a planet (in that it has characteristics strongly similar to Trans-Neptunian Objects (TNOs) but no physical characteristics which would be scientifically comparable to the planets in the Solar System, or even to the Solar System moons, should the scientifically correct answer be to place it in its actual category along with other similar objects in the Solar System, rather than force it into a category where it does not physically belong (such as planets)?
It depends on what physical characteristics one uses. As my list shows, Pluto does have physical characteristics that are scientifically comparable to the (other) planets in the solar system.

Is the list reasonable or not? Why not?

David Hall
2001-Dec-31, 03:53 PM
I don't think it was NASA per se. I'm sure the folks at NASA really want to send something up there as soon as possible. The problem seems to be more the bean-counters who won't allocate enough to fund a decent mission on time.

That and the current debate seems to stem on which is more important, Pluto or Europa. Everyone seems so keen on the idea that there might be LIFE up there that they don't really stop and analyze the situation carefully. I mean, we can get a mission to Jupiter quite easily. Mission after mission has been heading there for years. But it's quite difficult to get anything out far enough to visit Pluto. What, it's something like 8 years travel time?

Europa ain't going anywhere. I say we should focus on getting some data on all the major planetary objects before going back to explore more carefully what we have already visited. I'm also thinking about Mercury, which has had only one fly-by visit and is only half mapped. We may be missing something incredible simply because we aren't taking the opportunity to look.

bup
2001-Dec-31, 08:10 PM
An excellent point about whether composition should be an important part of determining planet status.

The definition of planet, in my mind, should be geared toward classifying things we haven't found yet - when we come to another object in another star system, how should we designate it?

If it's as big as Jupiter, but is essentially a giant ball of methane (forgive my ignorance - Pluto is mostly methane, right?), will we deny it planetary status?

Similarly, are the giants they are finding now, which have highly elliptical orbits, not planets because their orbits are so eccentric?

If it's as big as Jupiter, but is in the middle of that system's Kuiper belt (an impossible situation, granted, but for the sake of argument...) would it not be a planet?

If it's as big as Jupiter, but was captured by the system, rather than created by the leftover rubble when the star was born...?

etc.

For me, the answer to all the questions I've posted is 'still counts as a planet.' I agree with the criteria above - not a star nor brown dwarf, orbits a star or brown dwarf, bigger than anything that's not a planet.

So the debate is really the cutoff mass. Asimov's suggestion that it has to be big enough so that its gravity pulls it into something pretty close to a sphere, works for me - for solid planets, anyhow.

ljbrs
2002-Jan-01, 03:50 AM
Pluto is not being denied planetary status. It has two designations, because it fits both designations.

Planets tend to be those which formed around the star (Sun) out of the primordial matter from which the Sun, itself, was formed. Objects which are thrown into the Solar System (such as comets) tend to have a separate category.

I think that the astronomers in the IAU are interested in studying Pluto in both ways. I personally like a science which is able to change with new information. I, myself, do not get bothered with change. So, I can live with this easily. However, just ignore the second category, because Pluto is, first of all, a planet, and only secondly, a TNO (almost as an afterthought).

HAPPY NEW YEAR!

And HAPPY NEW YEAR! to

BAD ASTRONOMER PHIL PLAIT and to this wonderful site!

ljbrs /phpBB/images/smiles/icon_smile.gif

<font size=-1>[ This Message was edited by: ljbrs on 2001-12-31 22:53 ]</font>

ljbrs
2002-Jan-01, 03:51 AM
OH, YES... I HOPE NONE OF YOU HAVE VENTURED OUT ON "AMATEUR NIGHT"!

ljbrs /phpBB/images/smiles/icon_smile.gif

<font size=-1>[ This Message was edited by: ljbrs on 2001-12-31 22:59 ]</font>

GrapesOfWrath
2002-Jan-01, 10:17 AM
On 2001-12-31 22:50, ljbrs wrote:
Pluto is not being denied planetary status. It has two designations, because it fits both designations.
Does it have two designations? The FAQ on the IAU.org website (http://www.iau.org/IAU/FAQ/) says that the press release (http://www.iau.org/IAU/FAQ/PlutoPR.html) of 01/1999 "expresses the position of the IAU regarding the status of Pluto. The IAU considers the discussion closed with this statement and does not intend to reopen it in the foreseeable future."

The press release (http://www.iau.org/IAU/FAQ/PlutoPR.html) says that "The Small Bodies Names Committee of the Division has, however, decided against assigning any Minor Planet number to Pluto."

But "Ways to classify planets by physical characteristics are also under consideration," so I think the discussion of such characteristics, in this thread, is appropriate.

And Happy New Year!

<font size=-1>[Fixed formatting]</font>

<font size=-1>[ This Message was edited by: GrapesOfWrath on 2002-01-01 05:20 ]</font>

David Hall
2002-Jan-01, 02:25 PM
How about this. Instead of a dual classification system like we've been discussing for Pluto, we create a multi-layered system. We could classify objects something like this:

A: Large (Planetary) objects
Those that qualify under the planetary rules above

1) Large rocky bodies (Earth, Mercury)
2) Large gaseous bodies (Jupiter, Neptune)
3) Large icy bodies (Pluto, other large TNO's if found)
4) Other categories if found necessary (Hot Jupiters?)

B: Small (Planetoid) objects
Those that don't fall under the rules above.

1) Moons (Titan, Charon, The Moon)
2) Small rocky bodies (Asteroids)
3) Small icy bodies (Comets, Kuiper Belt Objects)
4) Other categories as necessary


Of course, these are just off the top of my head. It would take real experts to fix up a working system. Other sub-categories could be made and cross-categorization may also be possible. But this has the advantage of defining planets by both composition and orbital mechanics, while still leaving them open for inclusion with other objects. Pluto can retain its planetary status, but also still be included or considered as an icy Kuiper Belt object when the need arises.

Really, it's just a formal reworking of what we're doing already. Well, whaddayathink?



_________________
David Hall
"Dave... my mind is going... I can feel it... I can feel it." (http://www.occn.zaq.ne.jp/cuaea503/whatnots/2001_feel_it.wav)

<font size=-1>[ This Message was edited by: David Hall on 2002-01-01 09:41 ]</font>

Simon
2002-Jan-01, 03:47 PM
Hmm... Trans-Neptunian Object is a very fuzzy term...

I personally think Pluto could be classified as both a Kuiper Belt Object and a planet, I'm just fine with that. And I also think we should get a probe there before making any certain decisions about it.

And I believe I read a space.com article that said that NASA had decided to send a probe to Pluto and gotten funding, but didn't give a launch date. I may be mistaken there.

Hmm... maybe it's not only important to define what a planet is, but what it isn't? That's just a thought...

David Hall
2002-Jan-01, 05:23 PM
Well, as far as I can see, it's all still in budgetary limbo. The Pluto-Kuiper Express mission was basically cancelled, and NASA has been forced to scramble around looking for alternatives. The latest info I found was this one from May:

http://www.space.com/missionlaunches/missions/pluto_budget_010504.html

Something tells me that nothing promising has turned up since then. What with Congress stamping down on the budget, I don't see much hope for the near future. Only $500m for the entire mission? And it has to be launched by 2004? I don't see how it can be done with anything like the necessary thoroughness and quality needed. All we could get for that kind of money is a quick fly-by anyway.

I still think it's worth going in any case, even if we miss the 2004 deadline. Even a fly-by would tell us about 50x more about it than we know now. We still won't be able to get there before 2012. Ugh, I'll be an old man by then.

David Hall
2002-Jan-01, 05:31 PM
Speaking of which, I have a question for all you science-types out there. What about using the ion drive as developed for Deep Space 1?

Let's say we put up a probe with a drive that gave similar acelleration to DS1 and there's enough propellant to get there.

If we have constant acelleration, how long would it take to get there? I'm thinking both of a one-way, point-and-shoot fly-by, and an acellerate/turnaround/decellerate controlled insertion mission. If it's much quicker/cheaper/more convenient than previous missions, I don't see why it shouldn't be a top priority for NASA to get it working.

ljbrs
2002-Jan-02, 01:59 AM
All good posts!! I have trouble copying and pasting more than one post, but I have read all of them carefully.

I have not been able to access the IAU site to check out just what they have been doing. I get a bad (blank) connection which has forced me to re-enter BA several times. Obviously, I have not kept in touch with what they have been doing about Pluto in recent months. However, I am willing to go along with whatever the IAU does, since I am not a scientist, but merely a scientific cheerleader.

The idea of multiple categories for planets (and for all of astronomy/astrophysics, if such facilitated scientific study), makes really good scientific sense to me.

All of you who are posting in this thread make a lot of good sense, and I really do not have any personal preference, one way or the other about the outcome for Pluto. I only thought it was a good topic for discussion. I really can understand all sides of this controversy, and for that reason do not have any personal preferences.

Now, about ion engines... From the little I know about them, I think they might be just great for long journeys. But you all know much more about these things than I do. I know next to nothing about rocket propulsion and would fall flat on my face if I were to attempt to offer any advice at all.

Thanks for all of the input. I shall try the IAU site again when it is easier to access. I have had a link to it for some time, but neither the links offered here, nor my own link worked tonight. Perhaps the IAU astronomers are recuperating from New Year's parties....

ljbrs /phpBB/images/smiles/icon_smile.gif

GrapesOfWrath
2002-Jan-02, 03:08 AM
All the nine planets would be considered planets under my proposed scheme, and no other known body qualifies. Some of the TNOs that have been discovered might qualify.

Without each criteria, some objects would be classified as planets:
1) Identical twin stars
2) Charon, the moon of Pluto
3) Ceres
4) Our own moon
5) A baseball travelling through distant space

Some objects that would not be classified as planets under this scheme, but probably should be:
If Pluto and Charon were identical in size to Earth, they would not satisfy number 2.

So, how would we get around that?

ToSeek
2002-Jan-02, 01:55 PM
On 2002-01-01 12:23, David Hall wrote:
Well, as far as I can see, it's all still in budgetary limbo. The Pluto-Kuiper Express mission was basically cancelled, and NASA has been forced to scramble around looking for alternatives. The latest info I found was this one from May:

http://www.space.com/missionlaunches/missions/pluto_budget_010504.html



Some of my colleagues at APL are hard at work on this mission. Don't tell us nothing's happening!

30 Nov. 2001 - NASA taps APL for Pluto mission (http://www.jhuapl.edu/public/pr/011130.htm)


_________________
"... to strive, to seek, to find, and not to yield." - Tennyson, Ulysses

<font size=-1>[ This Message was edited by: ToSeek on 2002-01-02 08:56 ]</font>

David Hall
2002-Jan-02, 03:16 PM
Thanks TS. Good link. I'm glad to see there's still some hope.

Now, just so you all understand, I never meant to imply tthat the people at NASA and all it's related sections weren't trying. I was always sure that they're sweating blood to get missions out there. As much as you or I want to see it done, people with an actual career-stake in the projects would be twice as dedicated. And I support them 110%.

No, what worries me is what they're up against. Narrow-mided bureaucrats, budget-minded congressmen trying to grab more of the pie for their own pet projects and power schemes, and risk-adverse types worried about giving money to a "risky" or "futile" endeavour with no concrete or guaranteed payback. Especially when it'll take a decade to deliver. Things like this tend to fall pretty low on the funding totem-pole. I really feel for the NASA folks.

So, now they're hoping to get the New Horizons mission (I liked the PKE name better) launched in 2006, with a planned arrival date as 2016!! or later. Yeesh. I have to wait another 15 years to see Pluto, and that's IF they manage to get it up on time. Once again, it all comes down to the funding.

And whoohoo! I see that they have a Mercury orbiter planned too! I remember hearing something about it before, but this is the first time I've had clear info on it. MESSENGER, launching in 2004 and orbiting in 2009 (Why so long to get there?). Still a long way away, but within this decade at least. /phpBB/images/smiles/icon_smile.gif

Russ
2002-Jan-02, 04:08 PM
What I don't understand in all of this discussion is why everybody keeps refering to Pluto being "demoted" from being a planet. That is a misnomer. Actually, Pluto is up for reclassification. Reclassification is different than demotion. When you get re-ranked from Sergent to Private, THAT'S a demotion, the oppocite of a promotion. When you say that object is not a jet fighter it's a meatloaf, THAT's a reclassification.

With all that in mind, Pluto is being reclassified not demoted.

Lets us all pertend dat we is edakated gud an talk rat. /phpBB/images/smiles/icon_wink.gif

ToSeek
2002-Jan-02, 04:35 PM
On 2002-01-02 11:08, Russ wrote:
When you say that object is not a jet fighter it's a meatloaf, THAT's a reclassification.


But just try to convince a fighter pilot that's not a demotion. /phpBB/images/smiles/icon_wink.gif

ToSeek
2002-Jan-02, 04:40 PM
On 2002-01-02 10:16, David Hall wrote:
No, what worries me is what they're up against. Narrow-mided bureaucrats, budget-minded congressmen trying to grab more of the pie for their own pet projects and power schemes, and risk-adverse types worried about giving money to a "risky" or "futile" endeavour with no concrete or guaranteed payback. Especially when it'll take a decade to deliver. Things like this tend to fall pretty low on the funding totem-pole. I really feel for the NASA folks.

So, now they're hoping to get the New Horizons mission (I liked the PKE name better) launched in 2006, with a planned arrival date as 2016!! or later. Yeesh. I have to wait another 15 years to see Pluto, and that's IF they manage to get it up on time. Once again, it all comes down to the funding.

And whoohoo! I see that they have a Mercury orbiter planned too! I remember hearing something about it before, but this is the first time I've had clear info on it. MESSENGER, launching in 2004 and orbiting in 2009 (Why so long to get there?). Still a long way away, but within this decade at least. /phpBB/images/smiles/icon_smile.gif


I agree that funding is still a serious issue. So far all that's allocated is something like $30 million, which is about 10% of what's needed. Meanwhile, the Bush administration and the OMB seem to be against the mission for unfathomable reasons.

JPL for once had the better name for the mission: POSSE, or Pluto and Outer Solar System Explorer. Actually, I think they should rename it Tombaugh.

As for why it takes so long for MESSENGER to get to Mercury, I think it has to do with it taking more delta-V to orbit Mercury than to orbit Jupiter. So there are a bunch of flybys before it loses enough velocity to be able to get into orbit. The actual first encounter with Mercury is in 2007.

GrapesOfWrath
2002-Jan-02, 04:46 PM
On 2002-01-02 11:08, Russ wrote:
With all that in mind, Pluto is being reclassified not demoted.

Lets us all pertend dat we is edakated gud an talk rat.

1) It is not being reclassified either, as that IAU link made clear. Not yet, anyways.
2) Some people see it as a demotion, that may be part of the emotional involvement. There are no hierarchies or chains of command in the solar system, it is true, so there is no such thing as a business or military demotion in this case, but I can certainly see the analogy. A "planet" is a much more impressive term than an "object."
3) Science can and should reserve the right to change its classification--but it should also be more circumspect in its pronouncements. (Thirty years ago, families were told to have their infants sleep on their bellies--probably resulting in thousands of infant deaths per year, since recent advice to have them sleep on their back has greatly reduced infant mortality.) In the case of Pluto, is there a real need to change? What is that need?

bup
2002-Jan-03, 02:28 PM
On 2002-01-01 22:08, GrapesOfWrath wrote:
All the nine planets would be considered planets under my proposed scheme, and no other known body qualifies. Some of the TNOs that have been discovered might qualify.

Without each criteria, some objects would be classified as planets:
1) Identical twin stars
2) Charon, the moon of Pluto
3) Ceres
4) Our own moon
5) A baseball travelling through distant space

Some objects that would not be classified as planets under this scheme, but probably should be:
If Pluto and Charon were identical in size to Earth, they would not satisfy number 2.

So, how would we get around that?



Well, before I answer your final question, I think the 'approximately spherical' should be refined to 'approximately spherical because of its own gravity.' That gets rid of the baseball, even without #5 (> 200 km), and would get rid of a really, really big balloon.

Getting around two planet-sized things locked in orbit? What about this:
One of your criteria (I think) was - primary gravitational influence is a star or brown dwarf. What about, "any gravitationally influential body, other than a star or brown dwarf, cannot have the center of gravity between the two bodies inside the other body."

I'm not sure if that makes our own moon a planet, but it would Charon. Hmm. Something in that direction though.

Also, the criterion about the gravtitational influence should allow for a planet orbiting a twin star system, or star-brown dwarf combo.

Jim
2002-Jan-03, 04:39 PM
Thanks to ToSeek for the recent news about the Pluto mission.

I tend to agree with Angry Raisin's list of planet definers, although I'd increase the diameter to 2000km. This includes Pluto but excludes the asteroids and the KBOs/TNOs.

Frankly, I like having Pluto as a planet. No special scientific reason behind it, although GoW's list would provide some.

My feeling is that anyone who wants to demote Pluto from planethood status must be willing to foot the bill to catch up to the Pioneer probes and "correct" the plaques.

Russ
2002-Jan-03, 07:18 PM
But just try to convince a fighter pilot that's not a demotion. /phpBB/images/smiles/icon_wink.gif


Yeah, but I bet the pilot would be greatful he didn't try to fly off and chase the charlies on a meatloaf. /phpBB/images/smiles/icon_biggrin.gif That'd make a Katchupy mess on his G-suit. /phpBB/images/smiles/icon_frown.gif

GrapesOfWrath
2002-Jan-03, 07:31 PM
The problem with using "spherical because of gravity" is, no one is sure just how big that has to be.



On 2002-01-03 09:28, bup wrote:
Getting around two planet-sized things locked in orbit? What about this:
One of your criteria (I think) was - primary gravitational influence is a star or brown dwarf. What about, "any gravitationally influential body, other than a star or brown dwarf, cannot have the center of gravity between the two bodies inside the other body."

I'm not sure if that makes our own moon a planet, but it would Charon. Hmm. Something in that direction though.
Actually, that is the criteria number four from my list! The moon/Earth center of mass is inside the Earth, the Charon/Pluto center of mass is not inside Pluto.

ToSeek
2002-Jan-03, 07:41 PM
I was wondering about going back to the original, Greek definition of planets as wanderers (planetes) in the sky. Could visibility be a criterion? Is Pluto visible from Neptune? Are any of the asteroids visible from Mars?

(Actually, I'm deciding that this isn't a very good criterion, but I'd still be interested in answers to my questions.)

The Curtmudgeon
2002-Jan-03, 08:00 PM
I've got no business even being in this discussion, but reading all the other posts about how one distinguishes what's out there in the ether I've come up with a set of daffynitions that works for me, albeit I'm willing to accept that it might be too naive for real working astronomers:

A planetary object is any orbiting body whose primary is a star (or possibly brown dwarf, I'm open-minded about that); a moon is any orbiting body whose primary is a planetary object. A planet is a planetary object which does not share its general orbit (note: not specific orbit, since each asteroid has its own peculiar orbit) with other planetary objects; a planetoid is a planetary object which shares a general orbital area with other planetary objects (i.e., other planetoids)--moons don't count for this distinction (i.e., a planet can have moons without them making it a planetoid).

Thus the denizens of the Asteroid Belt and the Kuyper Belt both classify as planetoids, and the only distinction is "inner belt" v. "outer belt". Pluto/Charon are planetoids by this definition.

The reason I say I don't really belong in this discussion is that I don't know/understand enough about the whole zoo of other "thingies" floating around out there. Are there other "Trans-Neptunian" bodies besides Pluto/Charon and the Kuyper Belt? P/C doesn't come anywhere close to the Kuyper as I understand it, so if the only usefulness of the TNO designation is to group P/C with the KB then I'm agin it, as Granny would say.

I also realise that my classification doesn't do real good with non-belted asteroids, such as cross the Earth's orbit or Jupiter's Trojans. Come to that, a strict application of my definition to Jupiter would make it a planetoid, too, due to those very same Trojans, so I guess some sort of size distinction is necessary as well (i.e., one huge planetary object sharing its orbit with a bunch of smaller critters is a planet and the small junk are planetoids, whereas they're all planetoids if they're all close to the same size [within one order of magnitude, say]).

Well, as I say it's just an amateur's opinion. (I'm deprecating it mainly because the more I think it through myself, the less impressed with it I am.)

The (still orbiting the eggnog) Curtmudgeon

GrapesOfWrath
2002-Jan-03, 09:28 PM
On 2002-01-03 15:00, The Curtmudgeon wrote:
A planetary object is any orbiting body whose primary is a star (or possibly brown dwarf, I'm open-minded about that); a moon is any orbiting body whose primary is a planetary object. A planet is a planetary object which does not share its general orbit (note: not specific orbit, since each asteroid has its own peculiar orbit) with other planetary objects; a planetoid is a planetary object which shares a general orbital area with other planetary objects (i.e., other planetoids)--moons don't count for this distinction (i.e., a planet can have moons without them making it a planetoid).
I thought about the Jupiter Trojans as a counterexample before I got to that part of your post, but I'm still wondering about our own moon. What do you mean by "primary"? If you mean, the object that has the strongest gravitational pull upon it, then the moon's primary is the Sun. Then, by your definition, the Earth and moon would both be planetary objects.

And don't hog the eggnog. I want some too.

Donnie B.
2002-Jan-04, 12:39 AM
I wonder if it might be useful to incorporate the idea of "sweeping" an area clear of small objects in the definition of a planet. After all, except for the asteroid belt, the inner solar system is relatively clear of small objects (okay, sure, there are NEAs and such, and the occasional comet, but they're pretty rare).

Also, does our definition have to consider the early stages of a planet's formation? Does a blob of molten rock undergoing heavy bombardment still qualify as a planet, or do we need a separate classification?

ToSeek
2002-Jan-04, 02:42 PM
On 2002-01-03 16:28, GrapesOfWrath wrote:
Then, by your definition, the Earth and moon would both be planetary objects.


Certainly if our Moon were on its own, it would clearly qualify as a planet, as would some of the moons of Jupiter and Saturn.

SeanF
2002-Jan-04, 03:08 PM
I'm seeing a potential major motion picture here -- The Astronomer Who Went Up A Planet But Came Down A TNO. What do you think? Anybody wanna volunteer to play Tombaugh? /phpBB/images/smiles/icon_smile.gif

Seriously, though, I'm wondering what prompted TPTB to consider reclassifying Pluto in the first place. From the discussions on this board, there is obviously no clear-cut official definition of a "planet." Was the reclassification originally proposed simply because they felt Pluto didn't "fit" with the other eight planets, rather then that it didn't meet some established objective criteria?

If the former, I think it can be dismissed on its face. Now that we're starting to detect and catalog bodies orbiting other stars, we shouldn't let the characteristics of the eight (or nine) major bodies orbiting our own star determine our universal nomenclature, should we?

So, until somebody comes up with valid arbitrary criteria for determining "planethood" that everybody can accept, things should just stay the same, shouldn't they?

Granted, some will dismiss for personal reasons any criteria which excludes Pluto, but it seems that others would probably dismiss criteria which doesn't just because of the subjective feeling that Pluto shouldn't be included . . .

Just my two cents . . .

GrapesOfWrath
2002-Jan-04, 03:15 PM
On 2002-01-04 09:42, ToSeek wrote:
Certainly if our Moon were on its own, it would clearly qualify as a planet, as would some of the moons of Jupiter and Saturn.

No, I meant that under those criteria, both would be planetary objects, but not planets.

SeanF
According to the Sky and Telescope article (http://www.skypub.com/sights/moonplanets/9905pluto.html), Marsden has been trying to change the classification of Pluto for twenty years. I'm still not certain why.

John Kierein
2002-Jan-04, 06:10 PM
I think the companions orbiting the various asteroids, like Ida, are called moons. So, I don't think a moon has to orbit a planet.
http://antwrp.gsfc.nasa.gov/apod/ap990807.html

ljbrs
2002-Jan-05, 09:49 PM
If everything out there is a planet (or a star), then science will go out the window, and we all will be back to the mysticism of the ancients. Witness the problem of going from a flat Earth to an Earth-centered universe, then to a Sun-centered universe (and finally to a universe without a center). There are folks still alive who believe in an Earth-centered universe (perhaps even in a flat Earth), and there are some people who still believe that the Sun is the center of it all. People HATE CHANGE. We now are faced with an accelerating universe and there are folks who get abdominal cramps over that one, as well. Whatever scientists do will not change the facts of the universe. There will be future scientists who come along to add some previously missed data and that will ruin a lot of people's lives in their having to cope with change.

It does not matter what scientists call anything. The whole idea of classification is to facilitate the study of nature and of nature's laws. If everything is deemed to be a planet, then science must be thrown out the window and we will be back living like the ancients with all of their superstitions.

I grew up in a family with a history of science and got used to scientific change as a given. To me, scientific change is absolutely exhilarating!

ljbrs /phpBB/images/smiles/icon_smile.gif

GrapesOfWrath
2002-Jan-06, 11:15 AM
I don't think anyone is suggesting that we call everything a planet, we're just trying to consider what would be good criteria for the definition of planet. That seems to be the crux of the issue.

Classification is basic to science, there's no doubt about that, but there are a lot of issues to discuss. Just look at the clad wars over in biology.

ljbrs
2002-Jan-06, 08:54 PM
I don't think anyone is suggesting that we call everything a planet, we're just trying to consider what would be good criteria for the definition of planet. That seems to be the crux of the issue.

Classification is basic to science, there's no doubt about that, but there are a lot of issues to discuss. Just look at the clad wars over in biology.

I AGREE.

However, this *Pluto/Charon* business seemed to have been traumatic for many stargazers, et al., in recent years, and I think that it ought to be a marvelous subject for discussion here. Also, as you might note, I tend to be pretty stubborn about some things. This is not meant to mean that I am correct, but only that I am exceedingly stubborn. I am capable of change, but never quote me on that.

Perhaps if the astronomers had been (in the past) more particular in their designations, this problem would never have occurred to bother so many people. Astronomy is perhaps the most ancient of the sciences, so many bad habits have been produced by ancient astronomers and their descendants.

One possible criterion in categorizing a planet of the Sun might be that such planet would need to have developed together in the plane of the other major planets (in the thought-to-have-been primordial disk of our young Sun). I think that there is a need for careful designations. Moons should not be considered as planets. Late-coming additions to the planetary designations might have a hyphenated title to show this new classification.

Classifications of astronomical objects pertain to science and not to popularity polls. When an astronomical object is found to have been mistakenly named as one kind of object but is later found actually to have been another kind of object, scientists should stick to scientific methods and reclassify the object. Perhaps there needs to be a reclassification of all objects for scientific purposes only. Those same objects should be able (by the public) to be called whatever the public would wish to call them. Of course, this would most likely end in confusion (mixed with intense anger and fisticuffs) for everyone concerned.

Science evolves as it grows. I do not think that astronomy could be called a science if arbitrary rules prevailed in the science of astronomy itself which would never be followed (for instance) in physics. But physics is a relative newcomer (once considered a *natural philosophy*), particularly when considering some of its most recent discoveries.

Perhaps we should leave it up to the astronomers to make these decisions and go along with them if they make good sense. Tradition has no place in science. Remember the earth-centered universe and the problems involved where burning at the stake was (tragically) a probable punishment for challenging tradition (i.e., as in the case of Giordano Bruno). Astronomy has both serious and casual adherents. Professional astronomers cannot possibly please them all. The problem here, I think, is that there are so many astronomy lovers, casual, amateur, and professional (along with astrophysicists and cosmologists who are often off in a world of their own). Change is catastrophic to some people where astronomy is more like a religion than a science. I find change exhiliarating -- always have and always will. However, most people (understandably) seem to abhor change.

Now, I am not here specifically criticizing anyone. I just think that perhaps it is time for astronomers to be permitted scientifically to develop theories concerning these matters. Not being a scientist, myself, I shall leave that up to the scientists. I also think that controversy can be enlightening for all. Perhaps astronomers should keep all changes *under wraps* to avoid frightening everybody else. But *the truth will out*, eventually.

ljbrs /phpBB/images/smiles/icon_biggrin.gif /phpBB/images/smiles/icon_smile.gif /phpBB/images/smiles/icon_wink.gif


P.S. I stubbornly refuse (incorrectly, despite the cries of horror by the punctuation police) to put commas and periods inside of parentheses, unless such commas and periods are a part of the quotation. /phpBB/images/smiles/icon_biggrin.gif /phpBB/images/smiles/icon_wink.gif


<font size=-1>[ This Message was edited by: ljbrs on 2002-01-06 16:31 ]</font>

GrapesOfWrath
2002-Jan-07, 02:11 AM
On 2002-01-06 15:54, ljbrs wrote:
Perhaps we should leave it up to the astronomers to make these decisions and go along with them if they make good sense.
Well, so far, it appears that they've decided to not reclassify Pluto. Some of the links I read show that there is disagreement even amongst astronomers--but the bottom line is that the reclassification did not happen.

Pluto was once considered to have much more mass than it appears to have now. It hasn't shrunk, we just know more about it. If it had as much mass as it was once thought, we probably wouldn't be having this discussion--the orbit plane would not matter. Of course, the reason that it hasn't been reclassified is because it still has an order of magnitude more mass than the next closest object of the proposed type.

ToSeek
2002-Jan-07, 01:50 PM
On 2002-01-06 21:11, GrapesOfWrath wrote:
Of course, the reason that it hasn't been reclassified is because it still has an order of magnitude more mass than the next closest object of the proposed type.


Things could get interesting if we ever find a Kuiper belt object bigger than Pluto....

GrapesOfWrath
2002-Jan-07, 03:09 PM
Exactly. But until that time...

Until a couple years ago, Pluto was closer to the Sun than Uranus, for twenty years. That's as close as it gets. It's mean distance from the Sun is 5.9 billion km, but it was closer than 4.5 billion km. In a hundred years, it'll get out to 7.3 billion km, and be two magnitudes dimmer. What else could be out there? It may take a while to find out.

The Curtmudgeon
2002-Jan-07, 09:15 PM
On 2002-01-03 16:28, GrapesOfWrath wrote:
...I'm still wondering about our own moon. What do you mean by "primary"? If you mean, the object that has the strongest gravitational pull upon it, then the moon's primary is the Sun. Then, by your definition, the Earth and moon would both be planetary objects.

But the Sun isn't the body which the Moon directly orbits--it only orbits the Sun because the Earth does and it's orbitting the Earth. No, I wasn't thinking in terms of gravity so much as "geo"metry, if you'll excuse the planet-centric term here. I realise that orbits are elliptical not circular, and the "primary" isn't at the centre of the orbit but does (as I understand it) occupy one focus of the ellipse.



And don't hog the eggnog. I want some too.


We can be eggnog-planetoids in the same orbit. Anyone else in the Eggnoid Belt? /phpBB/images/smiles/icon_lol.gif

The (found a local place with great eggnog ice cream, too /phpBB/images/smiles/icon_smile.gif ) Curtmudgeon

GrapesOfWrath
2002-Jan-07, 10:47 PM
On 2002-01-07 16:15, The Curtmudgeon wrote:
But the Sun isn't the body which the Moon directly orbits--it only orbits the Sun because the Earth does and it's orbitting the Earth. No, I wasn't thinking in terms of gravity so much as "geo"metry, if you'll excuse the planet-centric term here. I realise that orbits are elliptical not circular, and the "primary" isn't at the centre of the orbit but does (as I understand it) occupy one focus of the ellipse.
The moon does orbit the Sun directly. The path of the moon around the Sun, if you were to draw it on a graph paper, is always convex.

And, for the Sun and Jupiter for instance, the center of mass is outside of the Sun, so the Sun doesn't even contain the focus of Jupiter's orbit.

GrapesOfWrath
2002-Oct-01, 11:48 PM
The August Sky and Telescope has two articles that discuss planet classification. The first is by Denise Kaisler, The Puzzles of Planethood, (p.32), and the second is by Alan Stern and Hal Levison, Toward A Planet Paradigm, (p.42).

Kaisler discusses mass and cosmogony as boundary markers for planethood, and points out that we already use mass to differentiate between stars and brown dwarfs. Some people believe that about 13 Jupiter masses should draw the line between brown dwarfs and planets. Others believe that cosmogony (the way the body formed) should be a factor.

University of California-Berkeley planet hunter Geoffrey W. Marcy is said to favor this definition: "A planet is an object that has a mass between that of Pluto and the deuterium-burning threshold and that forms in orbit around an object that can generate energy by nuclear reactions." She says Berkeley brown-dwarf specialist Gibor Basri favors: "A planet is a spherical non-fusor born in orbit around a fusor." A fusor is any body that fuses either hydrogen (stars) or deuterium (brown-dwarfs).

Kaisler points out that neither definition would apply to IPMOs (isolated planetary-mass objects), but I suppose the acronym takes care of that. /phpBB/images/smiles/icon_smile.gif

Stern and Levinson say they intend to publish their work in a future volume of the Transactions of the International Astronomical Union. In their opinion, a definition of planet should have the following qualities: 1) be based upon easily observed characteristics, 2) be quantitative, 3) be robust to new discoveries, 4) classify uniquely, 5) be context independent, 6) be uniquely deterministic, 7) involve the fewest possible criteria. In addition, it is desired that it be backwards compatible.

They analyze the possibilities, and conclude that a planetary body must be defined by an upper limit on size (low enough that it at no time had slef-sustained fusion reaction) and a lower limit (massive enough that its shape is determined primarily by gravity).

They claim that these criteria would include 22 of our solar system bodies--the four giants, the four inner rocky ones, seven moons, Pluto and Charon, 2 of the known Kuiper Belt Objects, and 3 asteroids (Ceres, Vesta, and Pallas). However, one of my previous posts (http://www.badastronomy.com/phpBB/viewtopic.php?topic=326&forum=2&start=8) had links that disputed the sphericity of the asteroids.

Then, they define a planet as a planetary body bound in an orbit around a single or multiple-star system. So, our solar system would have about 14 planets, they say (which would include Pluto). They go on to make other distinctions (unbound planet, planetary-scale satellites, double planets).

I'd like to consider my definition (http://www.badastronomy.com/phpBB/viewtopic.php?topic=326&forum=2&start=1) with regards to their criteria. Mine fail their number 5, for one, as they go on to explain that it means "An object's classification should not depend upon the nature of other bodies in its vicinity." However, they violate that one themselves, when they talk about a planet as being in orbit around a star.

<font size=-1>[Got rid of /phpBB/images/smiles/icon_cool.gif smilie]</font>

<font size=-1>[ Fixed url ]</font>

<font size=-1>[ This Message was edited by: GrapesOfWrath on 2003-03-10 14:06 ]</font>

moving_target
2002-Oct-02, 12:18 AM
I found this a while ago
What pluto has to say about KBO (http://www.brunching.com/morepluto.html)

just in case you need a small diversion from serious disscusion /phpBB/images/smiles/icon_smile.gif

Jim
2002-Oct-02, 12:35 PM
I love it!

So, the definition of "planet" should also include attitude?

P: I'm a planet. Read my lips. Pla-net. You got a problem with that?

**: I was just making a point.

P: I've got a point to make. Bite me.

Doodler
2002-Oct-07, 09:13 PM
Seven moons?
1)the Moon
2)Io
3)Europa
4)Ganymeade
5)Callisto
6)Titan
7)Triton

I think they missed a few (in no particular order):
/phpBB/images/smiles/icon_cool.gifUmbriel
9)Ariel
10)Miranda
11)Oberon
12)Titania

Each of them has a lot of similar characteristics with the aforementioned qualifications. Miranda holds its spherical shape as demonstrated by the folds in its surface indicating it had broken up and reformed over time. Another of the moons has evidence of ancient tectonic movement that occurred before the deep freeze set in.

On there own they'd be candidates on par with Pluto for planetary rights. And here's one for everyone to roll around in their mind too. Would a spherical body in orbit around a Brown Dwarf be a moon or a planet? And would that vary if the Dwarf were a stellar companion or a solo body? And what if, by some odd chance, that a lone brown dwarf where to turn up with a gas giant companion the size of Uranus or Neptune? Would that be a minor binary or a Star/planet? Keep in mind, large gas giants have been found up to 17Mj and Brown dwarves start around 30-40 Mj, its entirely possible that a co-orbital pair could be found. If memory serves, there have been a number of planet sized bodies found free floating in the Orion nebula. Such a pairing is outside possible. The definition of what a planet is or isn't (the core of the topic here) has a lot of room to grow. Why would not Pluto be a planet to the KBO's when the Earth and the other inner worlds are planets to the Asteroids? Where is the threshold? How can we attach such a narrow definition on a class of objects that have such awesome variation? Maybe we need to separate planets by type? Silicate Planets (Mercury, Venus, Earth, Mars), Gas Planets (Neptune, Uranus, Saturn, Jupiter and their extrasolar cousins), Sub-stellar planets (Brown Dwarves for those that can't fathom them as stars), and ice planets (Pluto and other massive KBO's)

We seem to be trying to package an awful lot into one word. Why not reclassify the lot of them if we want to do it to one? Create specific definitions for each type of planet, then the controversy over whether its a planet or not becomes a question of what its composition and size/shape relative to other objects of its class.

_________________
Never discount a possibility, always charge full price - HB Marketing Philosophy

<font size=-1>[ This Message was edited by: Doodler on 2002-10-07 17:16 ]</font>

kilopi
2003-Mar-10, 07:04 PM
On 2003-03-10 15:40, Kaptain K wrote:
I *think* you're still missing a /quote in there somewhere to distinguish the old post from the new addition. /phpBB/images/smiles/icon_smile.gif
Argh. I wondered where that post got off to when I tried to fix the original--I finally did it but I had no idea what had happened. Thanks for the heads up.

<font size=-1>[ This Message was edited by: kilopi on 2003-03-10 15:59 ]</font>

Kaptain K
2003-Mar-10, 08:40 PM
I *think* you're still missing a [/quote] in there somewhere to distinguish the old post from the new addition. /phpBB/images/smiles/icon_smile.gif

Yisrael Asper
2004-Apr-11, 08:22 PM
Petition called Create more Planetary categories and keep Pluto

http://www.petitionpetition.com/cgi/petition.cgi?id=6891
Petition to

Alan Boss, boss@dtm.ciw.edu, Head of the 13-member IAU group charged
with defining the word planet.

Whereas...The definition of the word planet has undergone many
changes starting with the supposedly nonfixed stars and sometimes
including the sun and moon. All this when it was thought that the
earth was the center of the universe. Such was the case with the
asteroids where the original definition was the minor planets between
Mars and Jupiter and so the first asteroid discovered Ceres was
called for want of a better term a planet and was dropped as a planet
when it was seen that it was really a member of a hitherto unknown
class of objects. Pluto too is a member of a hitherto unknown class
of objects and so like Ceres before it being the first of its kind
discovered it was called for want of a better term a planet just as
other galaxies were called nebulas and considered a part of our
galaxy when people did not know what they were. None of these
definitions are wrong it is just that they have added too our
language and in some cases are preserved only as archaic definitions.
People are used to many definitions in dictionaries sometimes they
are even when abstruse enough counterintuitive. People are used to
even only some definitions being shown in some dictionaries. Surely
since people only need a scientific definition of a planet in order
to not get confused about what laws apply but are used to the
classifications of planets in our Solar System as being a matter of
conventional rules beyond that, as witnessed by the continual
acceptance of Pluto and the historical evolutions of the term planet
within our solar system there is certainly no harm in keeping Pluto
as included among the planets as people can justly feel as they do
that there is scientific justification for the inclusion of Pluto
even when going beyond the usual characteristics of a planet that one
would look for. The gravitation of the planet Neptune was not enough
to explain disturbances in the orbit of the planet Uranus and so
under the mistaken assumption that there was a planet X that could
explain such disturbances it was predicted where that planet would be
and so was discovered Pluto. In the same way as our definitions of
the term planet has evolved as newer definitions for objects have
arisen but the older definitions are employed at times as well so let
it be with Pluto and perhaps it will more than just occasionally be
employed but continue to be in plain usage. The various definitions
proposed for the term planet are just part of what people already
think of as various definitions that at times they use for the term
planet just scientifically spelled out and would never be taken as
more. There should therefore be more categories of planets. This will
increase scientific description and accuracy. Their should be a
category called "Planetary Asteroid" which would include Ceres
because it is planet shaped and could even encompass Pluto if Pluto
is an Asteroid. Their should be planets called "Wandering Planets"
and "Far Distant Solar System Planets." All the planets except for
Pluto should be standardized for the universe in terms of their
definitions.

I, the undersigned, therefore petition the IAU to broaden the
definition of the term planet in accordance with the above with this
broadening preserving the full planetary status of Pluto.

Sincerely,

milli360
2004-Apr-11, 10:56 PM
The gravitation of the planet Neptune was not enough
to explain disturbances in the orbit of the planet Uranus and so
under the mistaken assumption that there was a planet X that could
explain such disturbances it was predicted where that planet would be
and so was discovered Pluto.
I don't think that, was, exactly, how, Pluto, was, discovered.

Welcome to the BABB.

Brady Yoon
2004-Apr-11, 11:04 PM
I think we should refer the planets, asteroids, comets, etc all as objects. Classification shouldn't be so organized-there isn't always a fine line between what's something and what's not.

Yisrael Asper
2004-Apr-11, 11:49 PM
"Yisrael Asper wrote:
The gravitation of the planet Neptune was not enough
to explain disturbances in the orbit of the planet Uranus and so
under the mistaken assumption that there was a planet X that could
explain such disturbances it was predicted where that planet would be
and so was discovered Pluto."

>I don't think that, was, exactly, how, Pluto, was, discovered.

>Welcome to the BABB.

Thanks for the welcome BABB. What is the part that you feel is not exactly how Pluto was discovered. All planets really have disturbances and maybe Uranus' disturbances were not big enough at all for a planet X really and Pluto isn't exactly where it was predicted it should be, nothing is. Still this minus the now known fact that Pluto is not Planet X is the story behind Pluto's discovery.