It's official: IAU says Pluto is a "plutoid"

[Trido (Justin)]

Next time I won't even bother.

[luvmybourbon]

We could call pluto a "claytons planet" planet when it not really a planet!

[renormalised (Carl)]

You'd be surprised at the number of astronomers who don't take any notice of what the IAU said about this matter. When you consider it was only voted upon by 250 or so delegates to the IAU Conference, and there's over 10000 professional astronomers worldwide, many of whom disagreed with the ruling, it was a bit much for the IAU to go and pronounce their decision.

Quite frankly, I think their criteria for the decision make no sense. On the basis of what they used, you could say there are no planets in the Solar System, because none of the planets fit the criteria.

Look at it this way... if they found a chunk of rock and ice out there as large as the Earth (which is always on the cards), what would you call that?? A Plutoid??!!!........hardly. That would be ridiculous. It'd be a planet, pure and simple.

[TrevorW]

Oh drats how do you think Mickey, Donald and Goofy are going to feel about this.

[stephend]

over 10000 professional astronomers worldwide

That's more than I would have thought. Where does that figure come from?

Things like this aren't usually decided by a vote; you'd expect it to be thrashed out at length in journals. Maybe it was?

[renormalised (Carl)]

Originally Posted by stephend

That's more than I would have thought. Where does that figure come from?

Things like this aren't usually decided by a vote; you'd expect it to be thrashed out at length in journals. Maybe it was?

Came from a press release of the IAU's about their decision. Nope, the whole shebang was done at the conference. They had 3 discussion panels and the usual side discussions, but that was where it was done. Then, after most of the guys went home, it was put to the vote, with about 250-300 delegates who were left there voting on it. There may have been references to changing Pluto's status in some journal papers, but no real knock em down, thrash it out discussion.

[Geoff45 (Geoff)]

Originally Posted by stephend

I think you are suggesting the whole thing needs to be renormalised?!

One perspective that might help is to imagine that Pluto's orbit was between Venus's and Earth's. If that were so, is it conceivable that someone would say "Venus is a planet and so is Earth but Pluto is not"?

.

If Pluto's orbit was between Venus and Earth, it might be a planet, if Ceres was between Venus and Earth it might be a planet and if my auntie had balls she would be my uncle.
A small object that is the major body in its neighbourhood obviously is different from a small body that is one of many similar objects in similar orbits.

By the way, why is nobody getting uptight about the fact that Eris is not a planet. It's bigger than Pluto and it has a satellite, so if people want to include Pluto, then they also have to include Eris, or is there some "logic" which gets around this?

[Trido (Justin)]

Logic does not come into this situation. There are those that passionately believe that Pluto is a planet and those that agree that it is too different to fall under the same category.

[stephend]

small object that is the major body in its neighbourhood obviously is different from a small body

Actually, if my hypothetical near-Earth-orbit Pluto enjoying the classification "planet" was moved out to Pluto's present orbit, it would be, by definition, exactly the same. Its neighbourhood changes, granted.

why is nobody getting uptight about the fact that Eris is not a planet.

I think it's just that Eris was discovered recently, while Pluto has been around all of our lifetimes. You're right, the logic is the same.

The discovery of Eris and a couple of other planets or plutoids of similar size has raised the spectre of a possible endless series of smaller and smaller planets, which has produced a cold sweat on many a brilliant brow. But necessity, the mother of invention, bless her, borrowing from taxation departments, has come up with the answer: a cut-off point.

Of course, to put a kilogram figure to it might sound pompous and arbitrary, so mass has been re-defined as "ability to clear one's neighbourhood" (not something we should aspire to).

The folly of this seems to me three-fold:
1) You'd never get a dinosaur to vote for it, nor any human who has an inkling of how likely we are to be smashed by one of the thousands of near-earth-orbit asteroids constantly whizzing past our neat, cleared corner of space.
2) IAU is careful to say their definition does not apply outside the solar system. That's because when we find planets orbiting other stars we haven't got a clue how clear their neighbourhoods are. Unfortunately, the same applies to the outer reaches of the solar system.
3) Clearing your neighbourhood takes time. Thus if we accept the definition, all we can say is that Pluto is presently not a planet, but may be when it has done some more clearing. This will at least amuse the angels.

These disputes arouse a herd instinct in all of us. They can descend into pure emotion. I object to the word logic being held up and waved like a talisman by either side. If you have a view, work it out, then write it out.

[Geoff45 (Geoff)]

I think one of the main problems in the IAU definition of a planet is the one that refers to "clearing the neighbourhood". Quite obviously, no planet has completely cleared its neghbourhood. That's partly why we see meteors. Even mighty Jupiter has the Trojan asteroids in its orbit. However, the situation with the first eight planets out from the sun is quite clearly different to the situation in the Asteroid belt, which is what I think the IAU were trying to capture. The problem is where do you draw the line? This is what I think needs to be clarified.
The situation beyond the orbit of Neptune is again different but similar to the asteroid belt and so IMO the objects there are distinguished from the currently recognised 8 planets and so deserve to be classed differently.

As for plutoids--it makes sense. In fact, more sense than asteroid: asteroid (star-like), plutoid (pluto-like). It may even sound natural in 20 years time.
Geoff

[skeltz (Rob)]

What !!!..i thought pluto was a cartoon character

[Chrissyo (Chris)]

Originally Posted by ghsmith45

Even mighty Jupiter has the Trojan asteroids in its orbit.

I think the idea is that the Trojan asteroids exist where they exist because of Jupiter. Similarly with other 'trojan asteroids' around other planets, corkscrew asteroids, etc.

It seems to me that there is a fair distinction between the asteroid belt/Kuiper belt (where Ceres and Pluto/Eris are found respectively) and the sample of other objects that can be found interacting with the planets.

"Having cleared its orbit" isn't a very clear definition, but I think it does make sense.

[Trido (Justin)]

I think the clearing its orbit thing refers to the bombardment that the planets underwent during its early evolution. These still occur because there is always junk coming into and out of the inner solar system, but no where near to the extent that it used to. When you look at close by objects, dating has put heavily cratered areas in the vacinity of several billion years of age whereas the less cratered areas generally show that geology or other unusual things have renewed the surface of the object.