Pluto Gets Consolation Prize, Will Thumb Nose at Astronomers Forever

Pluto is the ninth planet in our solar system. In our planetary mythology, it is the ninth planet, it is small, far away, cold, and there is an important cartoon dog named after it. But astronomers decided a while ago that Pluto is not a planet. That throws everything out of balance. Nine Planets is not just some number (nine, in this case) and the word "planets." It is a balanced equation, an iconic formula. Like the Holy Trinity. Or the Ten Commandments. Or the Three Stooges. Can you imagine a world in which there are only two stooges?

Well, Pluto has been given a kind of compromise .... a fully inadequate one ... but also a kind of honor.

From now on, Pluto is a Plutoid.

Plutoid is the word that will be coined to refer to the so called 'dwarf planets." So pluto gets status above asteroid. And, Pluto takes a special place as the root of the term Plutoid. Pluto is to Plutoids as Kleenex is to Kleenex.

This decision was made by the International Astronomical Union (the group that makes sure astronomers get paid above minimum wage, etc.)

Are you surprised that this has happened? So is everyone else.

"Most of the people in astronomy and planetary science community had no idea this was going to come out," said Hal Weaver of the Johns Hopkins University Applied Physics Laboratory. Weaver called the process that produced the new definition "sort of outdated, outmoded, archaic."

"In this day and age of transparency and mass communication, it seems a bit strange that such an important pronouncement would come out with so few people knowing about it, and, apparently, with no serious attempt to vet this with more people in the community," Weaver said.

Well, that guy obviously was not invited to the party...

This is only going to get more complicated. For instance, what do you do with a heavenly body like Ceres. It is large enough to be a planet if Pluto is a planet. So maybe it is a plutoid (which is not an asteroid). But it is siting right there in the freakin' middle of the asteroid belt.

Controversy will continue about this issue until astronomers come to grip with the fact that there is no clear expectation of discontinuity from a grain of dust to a massive gasseious planet. Or maybe there is, but you are not going to find this discontinuity at the size scale that includes the dust particle and, say, The Earth. Sure, there are differences in how these non-star solar system components act, like there are differences between clay silt and sand particles on the surface of Earth. But the differences are more nominal then they are boundary-like.

Astronomers: Pluto is a planet. Get over it.


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Astronomers: Pluto is a planet. Get over it.

Hear, hear!

By themadlolscientist (not verified) on 12 Jun 2008 #permalink

In the IAU Assembly where Pluto was demoted there actually more than one votes regarding its status: First one (number 5A) was that are Pluto, Eris and Ceres and their kind "dwarf planets"? The result was YES. (5B) Are these "dwarf planets" a subset of planets (a backdoor vote for pro-Pluto-is-a-planetists, who are partially to be blamed for "planet" in "dwarf planet"). Result: NO (actually this vote was the one that demoted these objects*). (6A) Is Pluto the prototype of a yet-to-be-named category of trans-Neptunian objects? YES. (6B) Are these objects to be called "plutonian objects"? NO.

Because of (6A) and (6B) this group was left without a name. That was fixed now, so this is not a new definition except for the additional odd constrain that a plutoid must have an absolute magnitude less than +1.

* Yes, objects. When people talk about Pluto's demotion, they usually neglect the fact that Pluto is only one of its kind, there are many such objects and probably more to be found.

The reasonable possibilities were (1) an unknown number [dozens] of planets or (2) eight planets. The members of the IAU had the good sense to choose the latter. The third choice, "there are nine planets, including Pluto, because my schoolbook told/its always been so/it's my favorite planet" was, well, stupid.

The wording of the resolution was unfortunate (it was written in a great haste), but the basic idea was good: planet is a large object (enough to be round) primarily orbiting the Sun and not a member of a population of similar objects. On the other hand the dwarf planets are fascinating worlds on their own right and not just debris so a new term for mid-sized objects was very appropriate.

Even though I don't count Pluto, Eris, Ceres, 2005 FY9, 2003 EL61, Sedna, Quaoar, Orcus, Varuna, Ixion, ... as true planets, it doesn't mean that I dislike them. In my opinion, Pluto for example is far more exciting object than some of the "proper" planets such as Mercury.

By Dunkleosteus (not verified) on 12 Jun 2008 #permalink

It seems almost foolish to try having one word for covering bodies as different as Jupiter and the Earth. That's the legacy we get for picking our words before we know what these objects really are. Curse you, pre-telescopic astronomers! The word planet is like a bedsheet which isn't quite big enough to cover all the discoveries we've made. Stretch it one way, and it'll slip off the other end. . . .

Personally, I liked the interim plan which would have given us 12 planets instead of 8 or 9. But any way you slice it, we know of more than twenty times more planets outside our solar system than in, and new exoplanets keep popping up.

What's truly ridiculous is that according to the IAU, dwarf planets are not in fact considered members of the populations which they would appear (in a naive viewpoint) to be members of: Ceres is NOT an asteroid.

As for blindly asserting "Pluto is a planet. Get over it." - this is ridiculous. From a solar system dynamics point of view (which seems to be the sensible way of defining which planets are more important on the scale of a planetary system), Pluto exerts far less influence than the other major planets. It is part of a population of similar objects in similar orbits (despite the IAU's somewhat crazy attempt to define things otherwise), unlike the other eight planets. So it would seem sensible not to regard Pluto as a major planet.

On the other hand, if you're interested in planetary differentiation, you might want to consider large icy objects like Pluto, and maybe some of the moons of the gas giants... similarly, it seems fairly sensible (from a planetary geology point of view) that the Moon, plus Jupiter's moons Io and Europa should be considered terrestrial planets.

If demoting Pluto from the list of major planets makes people have to learn a version of the solar system that isn't stuck in the 1930s, then so much the better. Complaining about people who adhere to somewhat antiquated views about how the diversity of life has come into being, while simultaneously trying desperately to hold on to an old view of the solar system that is inconsistent with more modern data seems a tad hypocritical, no?

"Or the Three Stooges. Can you imagine a world in which there are only two stooges?"

umm... That may not have been the best analogy you have ever made, Greg.

Personally, I still prefer hijacking the term created by sf author Wil McCarthy (for asteroids customized as luxury habitats/space yachts) and dubbing the medium-sized orbital bodies "planettes".

And there were at least five Stooges - what are they teaching in the schools these days?!?

By Pierce R. Butler (not verified) on 12 Jun 2008 #permalink

But, there were only ever three stooges at a time. Moe and Larry founded the trio along with comedian Curley. When Curley died of a heart attack they invited an old friend of theirs, Shemp to take Curley's place. When Shemp died of a heart attack Moe and Larry brought in comedian Joe Romita, Curly Joe. Unfortunately, by the time Curly Joe became part of the team Moe and Larry were getting a little too old to carry on as they had before, while Joe developed health issues and ballooned in weight. This changed the dynamic, and Larry decided to hang it up before it all went to shit on them.

Ah, they just should have grandfathered Pluto into the planet club.


I can't imagine what was eating the minds of the IAUoids when they decided that Plutoid was not a planetoid.

Nine planetoids! Perfetoid! The asteroids and the androids throughout the Cosmoids Rejoice!

Pythagaroid and Platoid are rolling in their Gravoids.

Those IAUoids must have been having a bad time with their hemorrhoids!

Any android will tell them of course there's nine planetoids.

It's the music of the Spheroids!



P.B: My point exactly! They were, indubitably, the THREE stooges. Yet there were five of them (ounting Shemp and Curly). (Like Alan Said).

M_Fox: My point exactly!

So we should call them "The Nine Planets" even if there's only eight, or if there's twelve?

By that logic, shouldn't we call them "The Five Planets"?

They were "The Five Planets" for much longer than they were "The Nine".

Janie: My point exactly!

Both five and nine are magic numbers. Eight is not.

Ok, you win, silly boy.

I'm not feeling much like putting up a dazzling display of witty repartee today, so put an asterisk beside this victory of yours.


Quite frankly, I think Mercury has gotten pretty uppity lately. Let's demote it too. Seven is most definitely a magic number.

Odd numbers seem more likely to "magic" than even ones. I wonder why that is? Six is definitely magic, though.

In all honesty, I think Pluto deserves the demotion. It's just a largest Kupier Belt object left.

It's just a largest Kupier Belt object left.

I'm not even sure that's accurate. Don't we know of a bigger one already, and suspect there may be thousands more?

Well, I was annoyed by your capitalization in the line "Pluto is to Plutoids as Kleenex is to Kleenex." Shouldn't that be "Pluto is to plutoids as Kleenex is to kleenex"? Or is Kimberly-Clarke still suing people who don't capitalize their product name, so to disguize knuckling under to the capitalists (and for the sake of symmetry) you capitalized "Plutoids" too?

By whomever1 (not verified) on 13 Jun 2008 #permalink

RE: Two Stooges

I can certainly imagine a world in which two stooges occupy them White House.

Oh wait, I don't have to imagine.