IAU Classifies Pluto & Eris As "Plutoids"

Kligat writes "The International Astronomical Union has decided that Pluto and Eris should be classified as "plutoids," alongside their 2006 classification as dwarf planets. Under the definition, the self-gravity of a plutoid is enough for it to achieve a near-spherical shape, but not enough for it to clear its orbit of its rocky neighbors, and the plutoid orbits the Sun beyond Neptune." Reader FiReaNGeL links to a similar story at e! Science News.

Comments

What a pantload

[Savior_on_a_Stick]

How they are classified means what to whom? Someone needs their grant pulled for gross misuse of time.

Re:What a pantload

[Jugalator]

I'd normally say it's about what to teach the kids and what's not as important -- a definition makes it easier to draw the line. However... This isn't about planets anymore, but plutoids. I think that moves more into the realms of advanced astronomy rather than schoolbooks, and then the definitions also matter less besides to split up things into smaller tables. :-p

Re:What a pantload

[Skye16]

As an aside, I think it silly that they're no planets solely because their barycenter does not lie inside of them. Do binary stars get classified as "Starloids" because their barycenter is between them? I didn't think so.

Of course, as I said below, it's all arbitrary anyway. It is inevitable that someone will be bitching about something no matter what definition we use.

Re:What a pantload

[Cecil]

Um, no, they're called "binary stars", which if you read the damn post is exactly what Rei is saying Pluto and Charon should be called: "binary (insert-appropriate-term-here)"

Rei even said it doesn't matter what you call them. Do you want to call them "binary planets"? Go ahead, from what Rei said in the post it's fine. All Rei said is that they should be prefixed "binary", just like stars are prefixed "binary". And I agree, they should be.

Other solar systems?

[Steve Max]

*sigh*
The new definition of "planet" was quite good. Clear, straight to the point, and easy to apply to any object. Now, they add a new category that applies only to our solar system?

Okay, we won't be seeing objects this small on other star systems, but the point remains. We are already at a time when we know these objects should exist in many other places in the universe. The classification shouldn't depend on their position inside our solar system, it should be generic enough that we won't have to change it (again) when we see one of those around Alpha Centaurii. I thought this was the single most important thing to come out of the previous discussion about what should be considered a "planet".

Re:Other solar systems?

[Jugalator]

As ridiculous it may seem, I'm pretty sure that this celestial body class was invented in some sort of weird attempt to satisfy people that didn't want Pluto to lose its planetary status.

"Now, it's at least a plutoid. Happy?"

Yes, from a scientific POV, it's pure bullshit, of course.

Re:Other solar systems?

[AstrumPreliator]

The new definition of "planet" was quite good. Clear, straight to the point, and easy to apply to any object. Now, they add a new category that applies only to our solar system? You do realize that the 2006 IAU definition of a planet requires a body to orbit the sun to be considered a planet, right? There are only 8 planets in the universe according to the definition at this time. You can follow the references back to the IAU's site for confirmation if you want.

Not only that but the third requirement is NOT easy to apply to an object. Assuming for a minute that the IAU definition of a planet required it to orbit a star, not the sun, it would be near impossible to ascertain whether or not the third criterion has been satisfied for potential planets in other star systems.

While I'm on a bit of a rant, anyone notice that Ceres isn't included in this new definition? Ceres is the third dwarf planet (by the IAU definition) if you don't know, it's orbit is in the asteroid belt. So Ceres, Pluto, and Eris are all dwarf planets. However, Pluto and Eris get to be Plutoids for being beyond Neptune. Good for them. I'm not sure how it's useful to classify trans-Neptunian dwarf planets again just so they can exclude Ceres, but I'm sure there's a reason that's definitely not arbitrary!

Re:Other solar systems?

[spacemandave]

Pluto is nothing if not very different from every other planet or that matter all the known bodies in the solar system. Except for the Plutinos, which are similar to Pluto in that they are all in 3:2 mean motion resonance with Neptune. Plutinos are themselves just one of several collections of resonant Kuiper Belt objects (the "Twotinos" at the 2:1 resonance being another). The resonant population is just a subclass of the Kuiper Belt, which itself contains other large objects like Eris, Sedna, and many more.

Pluto the 2nd largest of the as yet discovered Kuiper Belt objects. It is also the largest Plutino. In addition it is the 2nd largest known dwarf planet. I'm not sure why Pluto needs yet another classification category. It is certainly not justified on grounds of uniqueness.

Re:Calimero

[StDoodle]

Yeah, leave all that pesky "classification" and "definition" nonsense to hard sciences like Astrology and leave our fuzzy-wuzzy Astronomy alone!

P.S. Hail Eris!

Blaphemy!

[neuromancer23]

"This space intentionally left blank" - Principia Discordia

Let me summarize

[Bryansix]

They didn't do any more research. Nothing scientific was done. No more information was found out or cataloged. Nothing interesting happened. Just a bunch of people with too much time on their hands gave yet another name to a celestial body that orbits the sun. Frankly, who cares?

Earth too

[Anonymous Coward]

Earth should be classified as a dwarf planet as well because it hasn't cleared its orbit of rocky neighbors either.

Re:Earth too

[sznupi]

By saying this you (and people agreeing with you - yes, you know who you are!) show you didn't put any effort into understanding what "clearing neighbourhood" in planet definition means.

Specifically, it doesn't say that no other bodies in vicinity are present, but that all of them are dominated by gravitational influence of a planet. And that's definatelly the case with Moon and near Earth asteroids. But not with Pluto - it's in orbital resoncance with Neptune.

I actually really like this definition, fairly precise, universal, and avoids waking up one day in a Solar System with 20 or 30 planets, once we start discovering more Pluto-like objects. But somehow we have this nonsence of people attaching sentimental value to the notion of Pluto beeing a planet, which makes the whole deal unpopular.

And BTW, I don't like this latest "plutoids" thing; looks more like PR stunt. Definatelly doesn't really resolve anything, and if /. summary is to be trusted, is specific to our system.

Re:Earth too

[mangu]

I didn't know there was a hard limit of 10 planets in a solar system

There's no hard limit as a number, but there has to be some limit, otherwise every dust particle that orbits the sun should be classified as a planet.

I think the current definition is pretty good. Although I feel some sympathy for Pluto, I feel it's not quite right to classify a small body whose orbit intersects the orbit of a gas giant as a planet.

The irony of it all is that Pluto would never have been considered a planet if it wasn't for some error in observations that led people to believe its perturbation of Neptune's orbit to be much greater than it really is.

Re:Earth too

[sznupi]

You have to draw the line somewhere, especially if there's a chance that we'll end up with a lot more than 30 (it shows the signifance of given object for the Solar System as a whole vs. the significance of a lot of objects as quite homogonous group). For example, Ceres was ALSO initially considered a planet...right until the point when we started to discover the rest of asteroid belt.

All signs on heaven (and...only on heaven ;P ) hint that Pluto is simply a similar "first", discovered by chance because it was back then close to eclyptic and close to predicted position of Planet X (Uranus/Neptune - like object predicted by perturbations in Neptune orbit - later measurements shown them to be non-existent)

Re:Calimero

[vajaradakini]

No, definitions of planets are important if you're looking for them elsewhere and wish to classify the objects you find orbiting other stars. Besides, even as a first year astronomy student five years ago I knew Pluto wasn't a planet, they only made it official recently (and properly defined planets).

This plutoid business is silly though and only serves as some sort of consolation prize to the people who still wish that planets weren't actually defined and Pluto could still be considered among them. I mean, unless we're actually going to be applying this standard to objects we find around other stars (which I think would be silly, but then I'm not a planetary astronomer... so who knows).

I suspect that this has something to do with the upcoming international year of astronomy, which is all about getting the public excited about astronomy, semi-reversing Pluto's demotion (which appears to have been unpopular among non-astronomers) seems to be good for this.

Re:What about Ceres?

[kfort]

Yeah, I just question the decision to include 'clear the orbit' in the definition for a planet, which is what started this whole mess. If they had just stuck with the simplest definition of hydrostatic equilibrium (round shape) they could upgrade Ceres, keep Pluto, and deal with Eris. I think it would be a lot more exciting to have new planets than this constant squabbling over the status of Pluto

In other news

[whoami-ky]

Pluto officially defined as Pluto.
Eris officially seen as similar to Pluto.

Who really gives a flip?

There are objects out there of every size shape and configuration possible.

Nope - Not Happy - Pluto is a Planet to me

[gadlaw]

In the realm of things that don't matter except that I've been told for more than 40 years that Pluto is a planet then told by some 'Congress of Ass- tronomers' that it's not - screw those smug smirking bastards. I saw the Nova episode and hate every one of those ass-tronomers who happily conspired and worked on the planet demotion by vote. It's a planet and some power tripping douchebags can't vote otherwise. Now I hate this crop of Ass-tronomers.

Re:plutoids

[Tr3vin]

mickey: hey pluto, didja hear that i'm divorcing minnie? pluto: i don't blame you - i always thought she was a little crazy mickey: CRAZY?!? she's fuckin' goofy!! Pluto doesn't talk...

Re:Calimero

[Convector]

Should we also have made an exception for Ceres for historical reasons? It was thought to be a planet for some 50 years after its discovery until whole bunches of asteroids were discovered.