So, what is a planet?

[Quicksilvre]

Many of you know that the International Astronomical Union is meeting right now, and on Thursday, they are going to vote on a new definition of the world "planet." The recent (in the last 10-15 years) discovery of lots of Pluto- and almost-Pluto -sized objects in the solar system beyond the orbit of Neptune. All of the eight classical planets (Mercury to Neptune) will maintain their status, but Pluto is not nearly as secure.

The currently drafted plan (planet = anything round and more than 800km across that orbits the sun) keeps Pluto as a planet and adds

Chiron (Pluto's biggest moon, to be added because of its orbit around Pluto)
Ceres (the biggest asteroid in the asteroid belt)
2003 UB313 (farther from the sun than Pluto and a hair larger)

On top of all that, there are a bunch of other things that may or may not be classified as planets, depending on what else astronomers find out about them. Most of them have just numbers for names, so far.

CNN article

Space.com article

Caltech article

What does the Lounge think? As icky as its name is, 2003 UB313 is bigger than Pluto, and orbiting the sun, so it seems silly not to include it. I doubt many people would want to change their idea of the solar system, though.

[New001]

I really don't have a strong care either way, but I would rather see Pluto go away than add those three from that definition. I also don't mind the 9 there are now, if only because that's how it's been for years. I'm not sure whether I'd want it to stay the same or drop Pluto, though.

[pvn]

Wait, if Charon is to be classified as a planet, why not Luna or Titan, both of which are much, much bigger?

[New001]

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Wait, if Charon is to be classified as a planet, why not Luna or Titan, both of which are much, much bigger?

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I think because Pluto and Charon would be classified as a binary planet, where Luna or Titan are clearly moons.

[pvn]

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Wait, if Charon is to be classified as a planet, why not Luna or Titan, both of which are much, much bigger?

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I think because Pluto and Charon would be classified as a binary planet, where Luna or Titan are clearly moons.

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Ah. Was that in one of the linked articles? I only read the caltech one.

[LadyWrestler]

I want this settled right now!

#1. Pluto and Charon: Whichever is bigger is the planet. Call the other a moon, darn it! We are NOT having any double planets in this solar system!

#2. Add 2003 UB313 if it is larger than the larger of #1, and give it a decent name!!! Geez!

#3. Ceres: No! It is an asteroid!

#4. No way any of those other pretenders are getting in this planet club, period.

#5. 10 planets! 10 is a good number, a very gooood number! [img]/images/graemlins/smile.gif[/img]

[New001]

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Wait, if Charon is to be classified as a planet, why not Luna or Titan, both of which are much, much bigger?

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I think because Pluto and Charon would be classified as a binary planet, where Luna or Titan are clearly moons.

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Ah. Was that in one of the linked articles? I only read the caltech one.

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I'm not sure, I heard it sometime in the last couple days. Just verified it with Wikipedia.

[Sykes]

The reason that Charon is not a moon of Pluto is because Charon does not rotate around Pluto.

[Bjorn]

Aperently a descision was taken yesterday by world astronomers to demote Pluto and leave the solar system with eight planets. From what I understand the descision was made in quite a controversial way as well on the last day of the conference when a lot of delegates had allready left etc.

Either way I'm not entirely comfortable with this beeing an issue simply for the profesional astronomical comunity. Clearly a lot more people than that will be affected (at least philosophicaly) by what the outcome will be.

I for one whould much prefer to live in a planetary system with 10+ planets than one with just 8.

What do you guys think? Is this a desicion best left to a rather small "clique" of professional experts or should it be refered to a wider public?!?

/Bjorn

[jstnrgrs]

I think it ought to be, anything that orbits the sun is a planet. Moons should be considered part of their planet system, so in the case of pluto, it may be a two bodied planet (and the earth would be too for that matter). There might me millions of pieces of dust that would techinaclly be palnets in this defination, but I don't see a problem with that because any size criteria is arbitrary. If they want, they can pick a number and say that anything larger is a major planet. I don't care what number they pick, but I would recomend using the size of the whole planet system (including moons) since that is what ends up having an effect (on everything else) anyway.

The whole discussion is pretty silly, and doesn't make any difference anyway.