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.

What a pantload

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

Re:What a pantload

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

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.

Calimero

It's a stupid debate altogether. I image all the astronomers involved feel really good about themselves for making an impact. Why couldn't they leave well enough alone? Pluto will always be the ninth planet to me, despite Eris. Definitions be damned!

Re:

IMO classification can be a nice thing. It helps to reduce the clutter. However it seems that every now and then, something is discovered that 'refuses' to be classified.

Also, in Pluto's case, I think they should've made an exception for historical reasons. It should have remained the ninth planet while at the same time introducing a system for classifying objects. Every branch of science is riddled with exceptions, and it's nice for, for example, teachers to see their students get angry because there are s

Re:Calimero

I think this was a wise decision. You can't really aruge that "Pluto is not a plutoid", so maybe this will finally settle things.

Exceptions for historical reason serve no purpose other than confusing future students, and if that were our goal we would have elected Hillary, followed by Jeb, so that future students could be confused by the "Bush, Clinton, Bush, Clinton, Bush" line of presidents.

Oh, and Hail Eris, of course.

Re:Calimero

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:Calimero

Classyfing Pluto as a Plutoid is not silly. Classifying Jupiter as a gas giant is not silly. Classying Mars as a telluric planet is not silly, either. This is exactly what you pointed out when you said that classifications were useful to catalog objects orbiting other stars.
Now, what I think people are objecting to is the apparent lack of logic for the "planet" classification itself. You get objects as different as gas giants and telluric planets under the same umbrella, "planet". So, why not Kuiper belt objects ?
But regardless of what has been the actual ruling about Pluto, the main problem lies in the redefinition process itself. What is a tomato, a fruit or a vegetable ? For biologists, it's a fruit, for cookers it's a vegetable. Everybody gets on with it. Different names for different fields, it's not uncommon. It has been going for ages.
Now, what went through the mind of the IAU to think that the "planet" word needed a formal science definition ? The ambiguity of this word had been acknowledged for ages, and there was some disagreement among astronomers. They could just as well have kept on using accurate names, such as gas giants or kuiper belts objects. It's as if some day, the "International Biologists Union" decided it was a good time to formally define the word "bug". And ruled that only insects should be called bugs, and not arachnids.
Anyway, it's not a big deal.

Begging the question.

Classyfing Pluto as a Plutoid is not silly. Classifying Jupiter as a gas giant is not silly. Classying Mars as a telluric planet is not silly, either. This is exactly what you pointed out when you said that classifications were useful to catalog objects orbiting other stars.

You and GP are begging the question. Yes, classifications are "useful" to catalog objects orbiting other stars. But, what is the use of cataloguing objects orbiting stars, in the first place? What does it tell us? Does the classification of an object predict any properties of it that beyond those that were required to successfully classify it?

Two subpoints here:

1. You're committing a very common philosophical error, that I'll call ontological essentialism: the belief that there exists such a thing as a context-independent "correct" classification of things according to a given scheme. This error is leading you to think that there really must be a truth of the matter as to whether Pluto, as a thing in itself, is a "planet" or not.

   The response to this is that classifications aren't properties of things in themselves, but rather, are context- and purpose-dependent distinctions that people impose on them.

2. Astronomy is a natural science. Natural science is concerned with making predictions. The most natural use of classifications in natural science is, therefore, as a predictive apparatus: a classification has predictive value if, when you observe the properties of an object required to classify it correctly, you can use the classification to predict further properties that you did not observe.

   I've not seen anybody come even close to doing this for "planet." Once you observe all the things you need to observe to decide whether a celestial body is a planet or not, you're not in a position to predict anything else about the object.

   This doesn't mean that scientists can't use non-predictive classifications for genuinely useful means; non-predictive classifications can be quite useful for communicating with other people (if somebody says "planet," it may not allow you to predict a lot about the object, but it helps you guess what the other person may be talking about). But usually, those classifications don't really need to be very precise.

3. In any science, it pays to be skeptical about the validity of received vocabulary and classifications. I like the way one of my professors puts it: when faced with terms like "planet," it is often valuable to step back and, instead of seeing them as the names for distinct kinds of things, to see them as the names of distinct kinds of problems that the people who came up with the term were trying to solve.

   In this case, the problem is pretty simple. The ancients charted the movements of the lights in the night sky, and were concerned with formulating laws to explain their motion. The problem you hit right away when you start doing this is that a handful of those lights move in a manner that's very different from the vast majority of the others. Those weird, "wandering" ones are the so-called "planets," in the original sense. This goes back to point (1): the classification of some celestial objects as "planets" responds to the purpose of formulating and solving this problem.

   Guess what? We're not the ancients. We don't have their problems in explaining the motion of those things. We have super-powerful telescopes that show us all sorts of funny rocks in space that they could never hope to see, moving in all sorts of weird trajectories. We have a theory of Newtonian mechanics that explains their trajectories as a specific case of more general laws, without having to formulate laws of weird-space-rock-motion. Why are we keen at all to try to get a precise fit between what we see and their vocabulary? The reason we have problems with deciding whether something like Eris is a "planet" is because we know a lot more than the ancients did. Insisting too eagerly on the classification just demonstrates a failure to appreciate how very different and superior our understanding is.

Other solar systems?

*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?

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?

Also, it's patronizing. It's like trying to pass off Civil Unions as just as good as Marriage. You can try, but everyone sees through such cheap tricks.

Honestly, if you're just going to say no, say no. This is like saying "no, honey, you can't have a cell phone, you're only 12. but here, i got you this plastic cell phone that holds candy!"

Your daughter would be well within her rights to kick you right between the legs for excessive dickitry.

Re:Other solar systems?

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 [wikipedia.org] 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!

Just as good as "Alex and Nikki"

In college I knew a 'dancer' who had named her 2 breasts "Alex and Nikki"!
As I recall, they each had "...a near-spherical shape, but not enough for it to clear its orbit of its rocky neighbors..."
-I suppose naming them "Pluto and Eris" would have worked equally as well...

How irrelevant my past accomplishments

my award-winning 5th grade planet mobile becomes even more irrelevant.

Let me summarize

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?

Slight ommission

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.

The summary fails to mention one further requirement: For an object to be considered a true Plutoid, it must posses a "curiously strong" flavor.

Pluto on its way out?

First it got demoted, then given a brand new (and largely meaningless) title. I expect Pluto to get a pink slip any day now.

Re:Pluto on its way out?

Nah, they'll just stop paying it and let the problem work itself out naturally.

Galactic Lampoon's Summer Vacation!

Let's be honest here. We all know the reason Pluto was re-classified to throw off the Tom Tom of our, now lost, Galactic Overlords.

Galactic Overlords: "Tom Tom! Where is this "Earth"?!"
Tom Tom: "Make a left at the 9th Planet."
Galactic Overlord: "WTF?!?! There IS NO NINTH PLANET, Tom Tom!"
Galactic Overlord's Mother-in-law: "I told you, Rory! You should have made a right at Uranus! If you can't find a PLANET, HTF were you able to find my daughter's birth tube?!"
Galactic Overlord Jr.: "Are we there yet?"
Galactic Overlord: "Dammit! Don't make me pull over this Star Destroyer!"
Galactic Overlord Jr.: "I gotta pee!"
 

Re:WTF is Eris?

Eris, which measures about 70 miles wider than Pluto, is the farthest known object in the solar system at 9 billion miles away from sun. It is also the third brightest object located in the Kuiper belt, a disc of icy debris beyond the orbit of Neptune.

Re:WTF is Eris?

Eris, which measures about 70 miles wider than Pluto, is the farthest known object in the solar system at 9 billion miles away from sun.

Eris is not the farthest known object in the solar system. It is a member of the "scattered disk," a subclass of Kuiper Belt objects (KBOs). It is the largest scattered disk object (SDO) discovered so far, but by no means the farthest away. This [wikipedia.org] article has some nice diagrams that show the location of Eris relative to other known SDOs. There is another subclass of KBOs, called the "detached" objects, that are even further away. Sedna [wikipedia.org] is a member of this family.

Re:WTF is Eris?

IIRC it is a kuiper belt object that actually isn't on the same plane as the other planets. I think I actually recall it being found by accident because it isn't where we would expected it to be, most likely it is a captured object not formed by our suns accretion disk.

It is unlikely that any of the Kuiper Belt objects were captured from somewhere else. The Kuiper Belt is thought to have formed from the same accretion disk that formed the planets. However, it is thought that the original Kuiper Belt contained far more material than it does today, and that the objects were in more circular and coplanar orbits than we find them today. Due to an episode of giant planet migration, this original disk was scattered and depleted.

Many (but not all) of the observed dynamical features of the Kuiper Belt can be explained by giant planet migration.

What's in a name? A lot actually

Or in other words, what does the terminology matter?

Imagine if the former ninth planet had been named after Hemos, and then a class of similar objects given a derivative of that name. We'd have to put up with "Hemorrhoids circling Uranus" jokes until the heat death of the Universe.

Re:Earth too

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.