Pluto defines a Planet as being a Planet!

[MeteorWayne]

That's my question as well. The fact is, there WAS no definition before then. There were popular conceptions, common understandings, few of which agreed.

Was it the best definition possible? Probably not, but it was the first time an "official" definition had been laid out. It certainly sparked good conversation and thought leading up to the next attempt to refine it this year! :twisted:

 

[jakethesnake]

Let’s hope the IAU does a better job this time around…

 

[jakethesnake]

But you have yet to explain (at least to me) why you think it failed. Why is your posited definition better for scientific communication than one I'd support, or that the IAU would? Are you a research astronomer?

Actually I don’t think my definition is better than the IAU’s definition, I’m just saying that if you are going to pick an arbitrary definition of what a Planet is then Pluto is as good a place to start as any.

My personal belief is that the definition of a Planet should be based on solid science and the factors that cause celestial bodys to actually differ. Such as Gas Giants, or when a celestial body has enough mass to cause it to become spherical, or even more detailed geological aspects such as plate tectonics, which in effect would isolate the definition of a planet to only our solar system.

I think the IAU should leave their definition open ended, kind of a living document, adding to it as science adds resolution to our understanding of what differentiates these celestial bodies.

But for the love of God… not that if a planet has cleared it’s neighbourhood or not!

 

[Piratejoe]

When pluto was demoted to a dwarf planet I was pretty upset and Im still pretty mad over this. I know it's a silly thing to get so upset about but how the IAU demoted pluto was underhanded and unproffesional. How can I or my children take ANYTHING else they say or claim serriously when they have to resort to the childish games they pulled to get their definition of Pluto passed. If I remember correctly the people that were against pluto being a Planet waited untill most of the people that could vote on the subject were gone then the MINORITY of them got together and quickly passed the vote that got Pluto and other planets demoted. Now if im wrong please feel free to correct me.

I am very dissapointed with the scientific community of late, first their was the pluto travesty and recently the global warming information suppresions. If pluto is not a planet or global warming is real then why do some scientist feel the need to resort to suppressing the debate or having to resort to having votes when theirs nobody around to oppose you. If your right then so be it but let your argument stand on its own two feet with a honest back and forth on the matter. What they did to pluto was just wrong and in my opinion every one of the poeple that voted for Pluto being demoted should be kicked out of the IAU or another vote on what defines a planet should be held but this time with as many of the IAU members voting on the mattere as possible. What are the anti pluto scientists afraid of, a honest open discussion is always a good thing, but as things are they appear to have their way so are going to attempt to quiet the subject and claim the matter is settled.

It is FAR from over, mark my words things will explode when New Horizons arives and this debate flairs up again. Hopefully things will turn out better this time and all the need for backroom deals done away with.

 

[MeteorWayne]

I don't think it was as underhanded as you suggest. It's actually a difficult issue, and there was considerable debate and multiple proposals. In fact, there had never been a definition of what a planet was, so this was a first shot at setting a definition. Was it perfect? No, probably not.

I think a lot of the whining was from those who didn't agree, which you would expect. One of the most vocal of course was New Horizon's Principal Investigator, Alan Stern. As has been said, Pluto doesn't care, and it's still a darn interesting target as one of the largest of the Trans Neptunian Objects, and the archetype of the Plutino class of TNOs in resonant orbits with Neptune.

I think it's significant that the issue was not important enough to be readdressed at the 2009 General Assembly.

I'm sure it will come up again, and again there will be spirited discussion and an attempt to refine the definition.

BTW, just so you know, I'm in the Pluto is not a planet camp, for reasons I laid out in the lost archives of posts here. There are good, rational arguments to be made on both sides of the issue.

At the NJAA, my local astronomy club, the President and I have many spirited discussions as well, since he's on the Pluto is a Planet team. We'll do them at public nights, and we even gave a talk at a Mensa meeting where we debated it. We do it pretty lightheartedly, and take it as a serious scientific discussion, not the travesty of astronomical justice that it is so often portrayed as.

Besides, of course, I'm right :lol:

Wayne

 

[robnissen]

Surprisingly enough, I still like my definition of a planet. An object that orbits a star whose lower limit on mass is about the mass of Mercury and whose upper limit is where fusion begins about 13 times the mass of Juptier.

This definition is historically accurate from ancient times as all planets had mass >= to Mercury and <= Jupiter (which of course is less than 13X Jupiter) and when it was found that Ceres was dramatically smaller than Mercury it was dropped from the list of planets. Also, this definition is not solarcentric as it can be applied to any star system.

 

[BenS1985]

Maybe its me, but the taxonomy of planets is pretty poorly defined:

Planets
Dwarf Planets
TNOs
KBOs
Plutinos
Plutioid
Gas Giants
Terrestrial
and so on.

It seems that the general public has no idea what the differences are, especially since Pluto got knocked off the list of the Big-9.

I don't have a problem with Pluto not being in the classic definition of a planet. What I do have a problem with (personally) is where we draw the line, and how we classify an object. Ultimately, the taxonomy is pretty poorly defined. When it comes to elements, plants or animals, its pretty easy to define the differences between each major set and subset.

So I think the IAU really needs to sit down, and build a forward-thinking classification for objects in the galaxy. I would personally adopt a classification system similar to plants and animals. Something based on very general compositions, sizes, and properties that allows us to go forward with definitions for not only our solar system, but all others.

For example:

Body Type>Spheroid (planet), non-spheroid (cometary, asteroid)
Composition>Rocky, Gaseous (max pressure defines composition type)
Size> Major (>Mercury), Minor (<Mercury)

And so on. Special taxonomies could be added as our understanding of the solar system grows. We need a modular system, but one that has very strong reigns on what is and is not under classifications. It shouldn't matter if Pluto is in one classification or not, but that we have classifications at all....Which we really have a poor grasp on.

 

[MeteorWayne]

Well, you kind of defined the problem exactly. The general public wouldn't know a planet from a meteor from a comet from a star. Just look around at some of the posts here at SDC. And the SDC audience is FAR more educated and interested than the general public.

As I said, the IAU 2006 definition was the FIRST time the planet definition had been defined in any way.

Planets

Hydrostatic objects that have "cleared their orbits", admittedly a poorly worded definition.

Dwarf Planets

Objects large enough otherwise, but that are mere flotsam in the solar system. Yes, Even Ceres, the largest.

TNOs

Trans Neptunian objects, a clearly defined category which overlaps with Dwarf Planets above and other categories below

KBOs

Kuiper Belt Objects, again a clear category which overlaps with definitions above and below.

Plutinos

A specific subset of TNOs and KBOs with a specific (2:3) orbital resonance with Neptune. Like Pluto, the largest discovered SO FAR.

Plutioid

I think this category is worthless.

"Plutoids are celestial bodies in orbit around the Sun at a semimajor axis greater than that of Neptune that have sufficient mass for their self-gravity to overcome rigid body forces so that they assume a hydrostatic equilibrium (near-spherical) shape, and that have not cleared the neighbourhood around their orbit. Satellites of plutoids are not plutoids themselves.[1]"

It a reduntant reduntant repeat repeat of the more specific definitions above and below.

Gas Giants

Actually pretty specific to Jupiter, Saturn, Uranus and Neptune.

Terrestrial

Again, actually pretty specific to Mercury, Venus, Earth, and Mars.

 

[BenS1985]

Well, you kind of defined the problem exactly. The general public wouldn't know a planet from a meteor from a comet from a star. Just look around at some of the posts here at SDC. And the SDC audience is FAR more educated and interested than the general public.

As I said, the IAU 2006 definition was the FIRST time the planet definition had been defined in any way.

Planets

Hydrostatic objects that have "cleared their orbits", admittedly a poorly worded definition.

Dwarf Planets

Objects large enough otherwise, but that are mere flotsam in the solar system. Yes, Even Ceres, the largest.

TNOs

Trans Neptunian objects, a clearly defined category which overlaps with Dwarf Planets above and other categories below

KBOs

Kuiper Belt Objects, again a clear category which overlaps with definitions above and below.

Plutinos

A specific subset of TNOs and KBOs with a specific (2:3) orbital resonance with Neptune. Like Pluto, the largest discovered SO FAR.

Plutioid

I think this category is worthless.

"Plutoids are celestial bodies in orbit around the Sun at a semimajor axis greater than that of Neptune that have sufficient mass for their self-gravity to overcome rigid body forces so that they assume a hydrostatic equilibrium (near-spherical) shape, and that have not cleared the neighbourhood around their orbit. Satellites of plutoids are not plutoids themselves.[1]"

It a reduntant reduntant repeat repeat of the more specific definitions above and below.

Gas Giants

Actually pretty specific to Jupiter, Saturn, Uranus and Neptune.

Terrestrial

Again, actually pretty specific to Mercury, Venus, Earth, and Mars.

Yes, some of them have well defined characteristics, such as terrestrial and gas giants - I'm not arguing using those definitions are wrong. However, how do we use characteristics in the taxonomy of planet classifications? Where do TNOs fit? KBOs? Plutinos? Can you define Plutinos around another solar system? Those are the questions, IMO, that need answered by the IAU before they started hacking off what is and is not a planet. I think the way they did it was haphazard, and a shame for astronomy.

 

[MeteorWayne]

"Where do TNOs fit? KBOs? Plutinos? Can you define Plutinos around another solar system? Those are the questions, IMO, that need answered by the IAU before they started hacking off what is and is not a planet. "

What is so hard to Understand?

TNO:

http://en.wikipedia.org/wiki/Trans-Neptunian_object

A trans-Neptunian object (TNO; also written transneptunian object) is any object in the Solar System that orbits the Sun at a greater distance on average than Neptune. The Kuiper belt, scattered disk, and Oort cloud are three divisions of this volume of space.

Is that difficult to understand?

KBO:

Kuiper Belt Object:

http://en.wikipedia.org/wiki/Kuiper_Belt_object

"The Kuiper belt (pronounced /ˈkaɪpər/, rhyming with "viper"),[1] sometimes called the Edgeworth-Kuiper belt, is a region of the Solar System beyond the planets extending from the orbit of Neptune (at 30 AU) to approximately 55 AU from the Sun.[2] It is similar to the asteroid belt, although it is far larger—20 times as wide and 20–200 times as massive"

Is that difficult to Understand?

Plutino:

The term Plutino was never intended to describe extrasolar planets, nor was the IAU definition of a planet. It was intended to describe OUR solar system.

http://en.wikipedia.org/wiki/Plutino

In astronomy, a plutino is a trans-Neptunian object in 2:3 mean motion resonance with Neptune. For every 2 orbits that a Plutino makes, Neptune orbits 3 times.

By it's explicit definition it only refers to OUR solar system!

Is that hard to understand?

And BTW, I don't think Plutino included in the IAU planet definition; it's just the logical description of such objects in our solar system, which decribes the class (of some 20 objects) where Pluto is the largest example so far.

MW

 

[Fallingstar1971]

Planet:

The word planet came to us from a Greek element meaning “passively drifting, wandering, or roaming”

So in a way, EVERYTHING is a planet.

So the question isn't whether or not it is a planet. The question now is what "type" of planet. Pluto has a lot of the same characteristics as a comet. A comet very well could just be an ice asteroid. Both are "Planets" according to the original definition. But one type is a comet, another an asteroid, Moons can remain moons.

But even under that criteria, Pluto would have to be thought of as an inactive comet. (I have to admit it would be AWESOME to watch Pluto and Charon fire up as comets. Although that would probably spell the end for Earth. The SUn would have to be considerably stronger in the output department for that to happen, and the closer planets? would be fried)

HOWEVER on the other hand, nothing in the solar system is "passively drifting, wandering, or roaming”
Everything is gravitationally bound to the Sun or another body bound to the Sun and orbits can be calculated and predicted. No wandering or roaming there, so now NOTHING is a planet.

So I have to ask, what difference does it make? They will remain long after we are gone. Im sure that another race in another time will have a completely different approach. Perhaps the term "Planet" should be dropped as antiquated and a new word dreamed up. Perhaps the word Tenalp. That will teach those crazy greeks for inventing words that nobody can agree on!


Star

 

[Mobiusfiftyseven]

What I want is for Dwarf planets to be consitered planets, but only Dwarf. What im trying to say is call them planets, but just have them as a new class of planets.

 

[MeteorWayne]

That's exactly what they are.

 

[Mobiusfiftyseven]

People seem to make it not sound that way though, like being a dwarf is like being dead...

 

[Piratejoe]

It's not so much that Pluto got demoted even though I disagree with that opinion, its HOW it was done. Having one camp pass their views on what a planet is with only 424 members out of what 9000 members voting on it? Thats not even 5% of the total IAU membership! Many poeple will not like it but if the Majority of the body votes on the three proposed whats a planet and this version still stands then ok, the I's have it but as it stands right now it WAS underhanded.

Always ask yourself how would I feel, So how would the people happy with the current IAU's planet definition have felt if things were reversed. "On the last day of the IAU convention 424 IAU members stayed and voted on a what defines a planet. With their contriversial vote not only is Pluto still a planet but the solar system has several new planets with Charon and Xena with many more expected" I can tell you, ya'll would be up in arms screaming that definition does not stand since the majority did not vote. As things stand right now things are in the Anti-Pluto's a planet camps favor so they are going to try and blow this issue off and hope things die on thier own. However the only fair way to silance this issue once and for all is for the dang IAU to sit down and come up with something the majority agree's on.

 

[Valcan]

So we are all in agreement. Pluto is a planet and shall be called such from now on no changing science books needed.

Case closed tell the rest of the scientific comunity the debate is over.

 

[MeteorWayne]

No we ain't. Pluto isn't a planet, it's just a large KBO, specifically a plutino

 

[TheNative]

I think it was right to reclassify Pluto, I'm just not sure if I agree with the way it was reclassified. I think there needs to be a better system of planet classification. Here's my take on it.

Planet - Any body that is spherical due to it's own gravity and less massive than a star.

Planet subtypes

Major Planet - Orbits a star and also clears it's orbital path.
Major Planet subtypes - Gas, rocky, etc.
Gas planet subtypes - hot jupiter, saturn-like, neptune-line, etc.

Minor Planet- Orbits a star and does not clear it's orbital path.
Minor Planet subtypes - Rocky (asteroid), Plutino, etc.

Rogue Planet - Does not orbit a star.

Proto Planet - Orbits a star and has yet to and is projected to clear it's orbital path.

Planetoid - Not a planet. Any body too small to become spherical under it's own graity.
Planetoid subtypes - Asteroid, Meteoroid, Comet, KBO, etc.

This sort of method of classification would allow us to add in new types as they are discovered. Basically a system akin to the classification of plants and animals. I also think this could clear any animosity over Pluto, as it allows it to be a planet, just not a major planet. We would need to change from saying "there are 8 (or 9) planets in the solar system" to saying "there are 8 major planets in the solar system, and many minor planets."

 

[MeteorWayne]

Tonight on NOVA:

The Pluto Files
Take a cross-country journey with Neil deGrasse Tyson to explore the rise and fall of America's favorite planet.
Tuesday, March 2 at 8 pm

http://www.pbs.org/wgbh/nova/pluto/

To check local listings:

http://www.pbs.org/wgbh/nova/airdates.html

 

[MeteorWayne]

Emily Lakdawalla's TPS blog on the episode:

http://www.planetary.org/blog/article/00002364/

Found this excerpt interesting and VERY true:

"I know that numerous Pluto researchers were filmed for it, and it's clear they roped in numerous celebrities as well, including Jon Stewart and Stephen Colbert. Before you roll your eyes at that, I feel I should say that Stewart and Colbert do more and better coverage of space science on their satirical news shows than the "real" media do. Colbert especially is clearly a huge fan of space exploration and frequently mentions the goings-on of space missions both human and robotic in his roundups of the news at the top of his shows."

 

[MeteorWayne]

I must say, the NOVA episode left me shaking my head in wonder about what the big stink about.

In it, Alan Stern, the PI of the New Horizons mission, who screamed like a cat who had it's tail stepped on about the alleged "demotion" of Pluto, repeatedly used the term dwarf planet to describe Pluto. This is EXACTLY what the IAU resolutions adopted!!

http://www.iau.org/public/pluto/

"The IAU therefore resolves that planets and other bodies, except satellites, in our Solar System be defined into three distinct categories in the following way:

(1) A planet (note 1) is a celestial body that
(a) is in orbit around the Sun,
(b) has sufficient mass for its self-gravity to overcome rigid body forces so that it assumes a hydrostatic equilibrium (nearly round) shape, and
(c) has cleared the neighbourhood around its orbit.

(2) A "dwarf planet" is a celestial body that
(a) is in orbit around the Sun,
(b) has sufficient mass for its self-gravity to overcome rigid body forces so that it assumes a hydrostatic equilibrium (nearly round) shape (note 2),
(c) has not cleared the neighbourhood around its orbit, and
(d)is not a satellite.

(3) All other objects(note 3),except satellites, orbiting the Sun shall be referred to collectively as "Small Solar System Bodies".

Notes:
1 The eight planets are: Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, and Neptune.
2 An IAU process will be established to assign borderline objects to the dwarf planet or to another category.
3 These currently include most of the Solar System asteroids, most Trans-Neptunian Objects (TNOs),comets, and other small bodies."

Clyde Tombaugh's daughter had no problem with the AMNH display (when she visited it with Neil), though she did comment she wished it "was a little bigger"

 

[NateEvans]

pluto for planet hood

 

[NateEvans]

Aparently a planet must be large enough to sustain its own orbit now they call it a dwarf planet along with haumea eris(xena), ceres , and makemake

 

[MeteorWayne]

pluto for planet hood

Well that certainly added a lot to this resurrected discussion

 

[MeteorWayne]

Aparently a planet must be large enough to sustain its own orbit now they call it a dwarf planet along with haumea eris(xena), ceres , and makemake

Your terminology is incorrect. Any object in a solar orbit can maintain it unless acted on by other forces; that's basic Newtonian physics.

What you are probably referring to is the poorly worded part of the IAU resolution referreing to "clearing the orbit", not maintaining it.

Here's the text of the IAU resolution:

The IAU ... resolves that planets and other bodies, except satellites, in our Solar System be defined into three distinct categories in the following way:

(1) A planet is a celestial body that (a) is in orbit around the Sun, (b) has sufficient mass for its self-gravity to overcome rigid body forces so that it assumes a hydrostatic equilibrium (nearly round) shape, and (c) has cleared the neighbourhood around its orbit.
(2) A “dwarf planet” is a celestial body that (a) is in orbit around the Sun, (b) has sufficient mass for its self-gravity to overcome rigid body forces so that it assumes a hydrostatic equilibrium (nearly round) shape, (c) has not cleared the neighbourhood around its orbit, and (d) is not a satellite.

(3) All other objects, except satellites, orbiting the Sun shall be referred to collectively as “Small Solar System Bodies.”

....

As I have often stated, I feel the concept is in the right direction, but hopefully the wording will be improved in the future.

Wayne