Pluto: No Longer A Planet

Looks like they are already making "Honk is Pluto is still a planet" bumper stickers.

The new definition of a plant reads:

"a celestial body that is in orbit around the sun, has sufficient mass for its self-gravity to overcome rigid body forces so that it assumes a ... nearly round shape, and has cleared the neighborhood around its orbit."

Maybe I'm wrong, but that seems to imply that Neptune doesn't qualify either.
Can someone explain this?

How far will they go? Will we end up in several years time, that the only "planet" in our solar system is the one that supports intelligent life?

Intelligent life?? Which planet would that be? Certainly not the one I am on, where more print pages are devoted to Brittney Spears and Michael Jackson than any of the numerous real issues facing us.

I'm sorry if there was any misunderstanding. I of course meant Mars.

Quote: "Maybe I'm wrong, but that seems to imply that Neptune doesn't qualify either. Can someone explain this?"

I do not understand why you say it implies that Neptune does nor qualify. If it is because Pluto sometimes dips inside Neptune's orbit (so Neptune has not "cleared the neighborhood around its orbit"), then I think you read a bit too much into the definition. All planets have some asteroids/comets crossing their orbital paths, so then that clause cannot rule out Neptune alone. The clause is presumably there to rule out asteroid Ceres and Kuiper belt objects as planets.

If Neptune were tough enough to be a REAL planet, then would it not have sucked in Pluto to 1.) merge with its own mass, or at very least, 2.) forced pluto to become its moon? It seems that the inability to "clear its neighborhood" is the only failure, on Pluto's part, to maintain its planethood. But it seems to have "cleared its neighborhood" as well as other planets. Not every comet or asteroid that flies past Earth gets sucked in after all.

The debate reminds me a little of the difference between the english units pound feet (torque) and foot pounds (work). Many engineers use the terms very loosely, much to my consternation. But most knowledgeble engineers at least know the difference between the concepts, even if they use the terms loosely. Then there are others, who haven't a clue, and in using the terms loosely, come up with calculations that are pretty muddy, or just plain wrong.

For me, I think I'll continue to call Pluto a planet, and hope that people will figure it out in context. The hardcore astonomers may be as disappointed in me as I am in people who say pound foot when they mean foot pound.

I'm defending Neptune's position, because, gee... we don't want to lose another planet, do we?

As for Pluto, its an oddball and probably belongs to the Kuiper belt objects. Neptune fits nicely into the Titius-Bode law distance for planetary spacing, have a nice near circular orbit more or less in the plane of the ecliptic, etc. But then, that's not in the new definition! Oh well…

If you do not know the Titius-Bode law for planetary spacing, read about it in a download from my web page: Articles.

The 0 in the Bode "law" makes me squirm. The law would be far more elegant if it started with 1. In my view, if Fibonacci gets 10 points for his series, Titius and Bode only get 6 or 7 for theirs.

This is darn near entirely off topic, but a couple years ago, I walked the "thousand meter solar system" with my kids and others. It is one thing to say, and intellectualize, that earth is the size of a peppercorn on such a scale. It is another to actually do the walk, laying out these tiny planets in vast space. I'd recommend it to anyone. (Pluto, incidentally, is the size of a dot made by a ball point pen, and to see the 8" sun from there, you need binoculars.)

Even further off topic: One cannot do the walk and hold onto the notion that the earth is the center of things (even in out tiny solar system). In my country, there are those who believe that not just the earth, but Washington DC itself, is the center of the universe. I think they need to take the thousand meter walk.

The solar system appears to have an order. We have the rocky planets that formed close to the sun, the asteroid belt that was debris caught between the suns pull and jupiter/saturn/neptune forming and so could aggregate, and the gas giants. Beyond that objects could only aggregate so far, not to their self-gravitation limit used by the IAU to create their definition of a planet. I agree with them. There is the term of Trans-Neptunian object that has been battered around since god knows when. When many objects were found around pluto such as Orcus they called them "Plutinos" (yeah, stupid name. What are us astronomers like!) but then the Kuiper belt objects were discovered, first with (15760)1992QB1. Add in all the recent "planets" found, and it pulls pluto into disrepute. Plus pluto's orbit doesn't follow the solar plane. At times its even closer that neptune. Just to say finally that I see your point: there are too many organisations. Soon we may be in a debate between whether (90377)Sedna is a Kuiper Belt or an Oort Cloud Object!

Actually my point is that the classification is arbitrary. How is Mercury more qualified to be a planet then Pluto? Why isn't the moon a planet and the Earth Moon system a double planet system? No, this new definition is as arbitrary as the old one and brings nothing to the table. What benefit do we gain from downgrading Pluto? Nothing. No benefit. How many years will be wasted on this debate? Too many. In the end this was a self important group making an inconsequential decision that is of little to no benefit to anyone.

Point taken. "Planet" is simply a word that people can attach whatever meaning to that they wish. I suppose its a personal thing to some people that they have always known Pluto as a planet and will always consider it so, therefore the IAU holds no authority to the public. Aw well bless let the little group have their pacifier. Better they spend time discussing this that trying to classify anything new - they're awful at that. I still think its not a planet though :)

It just goes to show, astronomers are people too. I like the cold dark matter idea – the observed reality of the universe completely fails to match the theories, so 'cold dark matter' is 'invented' – not discovered, because it's cold and dark and you can't directly observe it – and low and behold! The theory is saved! Any other scientist would be pilloried for this sort of thing, but it seems to work for cosmologists.

Reality has not changed very much. Pluto is still a planet as the word is understood by 99.99% of English-speaking people and I very much doubt whether Pluto is worried about how a group of scientific bureaucrats describe it. All that has happened is that we have been told that we may not call it a planet because that is now politically incorrect. I rather enjoyed the Yahoo reference to Ceres being a planet in the 1800s - how much has it shrunk since then? It should be fun watching the Academie Francaise reacting to being told by a small group meeting in Prague that they must change the definition of a French word... I suppose the next step is that I shall be told I may no longer call the object which I used to dig my father's garden when I was a boy a spade since it is not big enough to meet the new definition.

Pluto demoted. Do they really think its a good idea to piss off the god of the underworld, the god of death itself? It also rules volcanoes and atomic energy. Retribution may be swift!

Excellent point, I didn't even consider the fact we are basically offending one of the most powerful of the greek gods. I hope he realizes my post was satirical, though "king of the underworld" doesn't exactly scream sense of humor.