August 24, 2006 7:40 AM PDT

Pluto: And then there were eight

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January 25, 2006
Pluto has just been demoted.

The celestial body, long known as one of the nine planets of the solar system, will now be considered a "dwarf planet," the General Assembly of the 2006 International Astronomical Union ruled in a vote Thursday in Prague, Czech Republic.

Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus and Neptune will be defined as "classical planets."

Pluto

Three other bodies had been contending for planetary status as well: Ceres, the largest-known asteroid; "Xena," the nickname for 2003 UB313; and Charon, which has been considered Pluto's moon.

Ceres and "Xena" will now share "dwarf planet" status with Pluto. Charon, it has been concluded, will be grouped with "small solar-system bodies."

The IAU said in a statement on Thursday that the definition for planet is now officially "a celestial body that (a) is in orbit around the Sun, (b) has sufficient mass for its self-gravity to overcome rigid body forces so that it assumes a hydrostatic equilibrium (nearly round) shape and (c) has cleared the neighborhood around its orbit."

"More dwarf planets are expected to be announced by the IAU in the coming months and years,"a ccording to the IAU statement. "Currently, a dozen candidate dwarf planets are listed on IAU's dwarf planet watchlist, which keeps changing as new objects are found and the physics of the existing candidates becomes better-known."

About 2,500 members of the IAU, a community of astronomers from around the world, have been meeting since late last week to debate and vote on a series of resolutions that include definitions of solar-system bodies. The IAU General Assembly is held every three years. This session, four terrestrial bodies in particular have been the focus of the debate--the most prominent being Pluto, which was discovered in 1930.

Varying proposals from IAU members included referring to these smaller terrestrial bodies in different areas of the solar system as "planetoids" and "trans-Neptunian objects." Another proposal referred to the smaller objects as "plutonian objects." Yet another proposed the idea of a hierarchy of "planets," "dwarf planets" and "small solar-system bodies," according to the IAU. Still others wanted to keep Pluto as a planet but come up with alternatives for the other three.

IAU President Ron Ekers and other members of the IAU board are expected to hold a press conference Thursday on the final outcome of all the resolution votes in Prague.

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52 comments

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Bad Decision
I could write a long list of objections to this decision - but there is one very clear one - ask a school kid what they think about it.
As for the way the debate went - it started well, but then it became pure sophistry! Any decision was going to be arbitrary, lines have to be drawn somewhere.
A compromise to include Pluto, Xena and Ceres but not Charon was easy or can astronomers not do simple arithmetic? I can and here's a clue Barycentre or >50% Mass similar measurements different arbitrary line, there'd be no Planet Charon based on Mass, though personally if its round I'd have it - I'd even include Moons of other planets, but thats a whole other debate. As for the "'our Moon moving outwards and becoming a planet so what would we call it?' objection" (assuming the sun didn't expand first and we were still here several billion years from now to care)I suggest a good name would be "the Moon". I take it the "top" astronomers will now want to downgrade eighty or so elements from the periodic table because after all there are too many to learn, and some are more important than others, or how about the month of February, it acts very odd for a calendar month? Lastly the 'classical planets' are - and always will be - the Sun, the Moon, Mercury, Venus, Mars, Jupiter and Saturn - find another word smartasses!
In short have as many divisions of planets as required for clarity, but astronomers are supposed to be clever people (I would have thought so but apparently not), context is a wonderful thing.
Posted by eek10bears (1 comment )
Reply Link Flag
Bad Reasoning
You could also ask a school kid where babies come from and more often than not, you wouldn't get the correct answer. Including Pluto, Xena, and Ceres would mean adding dozens more, even if Charon were left out.

"Barycentre or >50% Mass similar measurements different arbitrary line, there'd be no Planet Charon based on Mass"

Maybe you can do simple arithmetic but you cant articulate a complete thought.

Also, it wouldn't be up to astronomers to downgrade the periodic table. The periodic table is quite straightforward. How many protons you got? 5? Ok, you are Boron. Astronomy and Astrophysics is quite a different subject. All in all, this is rather arbitrary. Just as there are terrestrial planets and gas giants, there are now dwarf planets. To get so worked up over an issue because you were taught in elementary school that Pluto was a planet is quite ridiculous.

I do agree that the word "Classical Planets" is not proper since it is the name given to all the non-stellar regular celestial-bodies that can be seen with just the naked eye. Maybe something like, "The Primary Nine" would work. Also, implying that a group of people are not clever because they won't define a word in such a way that would please people for the sake of tradition (rather for scientific reasoning) isn't very clever.
Posted by britt_brattany (1 comment )
Link Flag
Clearing the neighborhood
If Pluto isn't a planet because crossing the orbit of Neptune means
that it hasn't cleared its "neighborhood," why is NEPTUNE still a
planet?
Posted by gpskratz (1 comment )
Reply Link Flag
very good question
I'd be interested in hearing a very good answer - unfortunately I
don't have one myself.

Maybe because it's bigger? 8-)
Posted by Dalkorian (3000 comments )
Link Flag
possible "good answer"???
I replied to this comment yesterday claiming that I also was
interested in a good answer to this question. I may have found
one, I'll let you decide.

<a class="jive-link-external" href="http://stardate.org/resources/ssguide/pluto.html" target="_newWindow">http://stardate.org/resources/ssguide/pluto.html</a>

<a class="jive-link-external" href="http://news.nationalgeographic.com/news/" target="_newWindow">http://news.nationalgeographic.com/news/</a>
2001/02/0216_Pluto.html

Basically, it looks like the argument is that (most of) Pluto's
orbital path is within the Kuiper Belt (I hadn't realized this
before). Therefore, we're missing the real argument against
Pluto's planetary status - it's not because it crosses Neptune's
path but instead because there are other Kuiper Belt objects that
are also within Pluto's path.

Since Pluto hasn't got the "guts" to clear out it's "yard" (IE: there
are other Kuiper Belt objects in it's orbital path), it's been fired
as a planet.

Anyone have an argument against that claim? Please post links
as I have done above, I don't care how you "feel" about Pluto
(personally, I couldn't care less whether or not Pluto is a planet -
it's status won't put food on the table for me:)).
Posted by Dalkorian (3000 comments )
Link Flag
science
my science teacher taught me wrong?
Posted by chuckedward (1 comment )
Reply Link Flag
yup
Yes, your science teacher was an idiot and everything he/she
taught you is now suspect.

LOL.

Sarcasm aside, why are some people so attached to this little
iceball way out there? What difference does it really make if we
call Pluto a planet or not? Will people starve because of this? Will
people get fired and become unhirable? Will anyone DIE?

Besides, just last week they claimed there was 12 planets, not 9.
Now they have "adjusted" that to 8. Next week we might have 9
again, or maybe 10 even (go Xena go! - lol) ...
Posted by Dalkorian (3000 comments )
Link Flag
why
what are we not calling pluto a planet. does the science community have nothing better to do than take away our planets
Posted by firestarter (43 comments )
Reply Link Flag
because
You get to keep the first eight. The ninth is going towards taxes.
Posted by Seaspray0 (9714 comments )
Link Flag
Taken
No one has taken away any planets! In fact we've made the soalr system larger not smaller: you are forgetting that we've promoted Ceres and "Xena". Last time I checked 8+3 is more than 9.
Posted by kdconod (8 comments )
Link Flag
things change
get used to it
Posted by epiccollision (105 comments )
Reply Link Flag
But...
...the more things change, the more they stay the same. So you're saying Pluto is still a planet?
Posted by J_Satch (571 comments )
Link Flag
Wait a minute...
...I thought Pluto was a dog!
Posted by J_Satch (571 comments )
Reply Link Flag
Science must change. It is the way it works.
Science changes as greater information is gained and understanding evolves. Science is not set in stone like so many religons. Science is a living evolving understanding of our surroundings. The Pluto downgrade is great because it reflects the evolution of our understanding. Now we have Dwarf Planets and many objects in our solar system can also be better classified.
Posted by Stan Johnson (322 comments )
Reply Link Flag
Science?
It really doesn't have anything to do with science. It's just a bunch of geeks making an arbitrary descision. Science refers to the study of physical phenomenon; this has nothing to do with that. It's just a bunch of people's opinions. Obviously, we are constantly going to learn new things. But, arbitrary descisions are not science. For the sake of sanity and reasonableness, they should just keep Pluto as a planet and make the dwarf planet status for new stuff that meets the critera for that. The whole thing is just an ego trip for those who changed the classification. (Haha look at me, I downgraded Pluto--aherr aherr aherr)
Posted by MrHandle (71 comments )
Link Flag
Subject line:
Personally, I think it would be nice if they'd just left this whole
thing alone. How many years is it we've gone without a definition
for 'planet' and done just fine? 300 years? 400 years? 500 years?
Why can't they just keep doing it on a case by case basis or
something like they've done for however long?

Not that I think it matters for the general public. Those that want
to agree with the council of astronerds will change the way they
think of Pluto, those that want to think of Pluto as a planet will
continue to do so, not giving a rip if someone else says that
Pluto isn't a planet. Or doing it out of habit. I for one will
continue to refer to Pluto as a planet (and saying "whatever"
whenever someone tries to correct me).

As for Plutos moon, Charon, I don't get why that would be up for
consideration anyways.
It orbits Pluto. It's a moon.
Posted by Dr. B (91 comments )
Reply Link Flag
Regarding Pluto and Charon
Charon does not orbit around Pluto. Pluto and Charon orbit around each other.
Posted by Pablo_Corinthian (1 comment )
Link Flag
I agree
I agree with the last comment. If Charon orbits Pluto the Charon in a moon. Perfect sense.
Posted by swokjr (8 comments )
Link Flag
But.
That's no moon, it's a spacestation.

Ok, forgive me but it's friday afternoon before I go on vacation.
:D
Posted by Sboston (498 comments )
Link Flag
binary planet
well, charon doesn't exactly orbit around pluto, they orbit around eachother like a binary star would. thats why they were considering Charon
Posted by chipmonkey (2 comments )
Link Flag
They're just regrouping them...
That's what it sounds like anyway. Why not just teach the first 8 as "classical planets" and the 3 as "dwarf planets" geez, there will continously be planets added to our solar system.
Posted by PCCRomeo (432 comments )
Reply Link Flag
People who defend
Pluto as a planet are tools. I learned it as a planet and i like it that way... but guess what they are only changing the definition for themselves- astronomers- not you snivelling whiney people, simply so that they can communicate amongst themselves and mean the same thing. Lets face it none of you can define a planet, so they came up with something and you dont like it? Who cares!!!?!?!?

You are more than welcome to still call it a planet if you like.
Posted by volterwd (466 comments )
Reply Link Flag
get your head out of the 7th planet
What's with the personal attacks? You can call it a planet if you like but you would be wrong. The scientific definition is the only one that matters, no matter how many times that definition changes.
Posted by TucsonAlexAZ (53 comments )
Link Flag
Has the Pluto delegation objected yet? Sun refused to shine?
Wow, such an important decision, it affects the motion of all
bodies in the Solar system! How does the President of Mars feel
about this important decision? HELLO! A bunch of "scientists"
who know NOTHING about Pluto (or maybe some of them went
there and can claim something with certainty?) decided to
change the definition of the word they came up with in the first
place, completely arbitrarily. They travelled to three conferences
in very nice places to do so. They still know nothing and their
decision and nomenclature are still meaningless, but DAMN,
they have cool jobs for geeks whose top love affair is that with
Xena!
Posted by g_m (18 comments )
Reply Link Flag
Not to worry...
This "decision" was made by less than 10% of the astronomers in the world and backed by a small minority of the attending delegates who "snuck it in" (they oughta go into politics), so it's rather unlikely that it will stand up to the coming backlash simply because of the way it was done. Pluto is only "in the doghouse" temporarily.
Posted by GlennAl (25 comments )
Reply Link Flag
Pluto had to go
It never fit the standard pneumonic "Mr. Vem J. Sun" so astronomers kept forgetting it, which was very embarassing for them. Also, 8 planets matches up better with the "8-fold way" of high-energy physics and Buddhism. Plus, when Disney named Mickey's dog Pluto, he basically signed its death warrant (as a planet). Nobody took Pluto seriously after that. However, I think that astronomy could redeem itself by naming all new minor planets after cartoon characters. To inaugurate this new tradition, Ceres should be re-named Goofy and Charon re-named Donald. And instead of classifying them as "minor planets," which is very boring, they should call them "Mickey Mouse planets." Think how easy this would make it for schoolchildren to get good grades on tests.
Posted by dmm (336 comments )
Reply Link Flag
Absolutely
My thoughts exactly, like you read my mind! Also, the forum should have spent more time focusing on Uranus, and afterwards clear up that it's not the size of Venus, but how it orbits that matters.
Posted by Seaspray0 (9714 comments )
Link Flag
correction?
The game "Trivial Pursuit" claims that the Disney character Pluto was named before the planet. I checked Wikipedia and got the following: planet discovered in 1930; cartoon dog named Pluto that same year in honor of the planet.
Posted by dmm (336 comments )
Link Flag
This will cause DISNEY stock to take a hit.
At least that company that makes hair removing vibrators for women can quit holding it's breath... VENUS is still in.
Posted by disco-legend-zeke (448 comments )
Reply Link Flag
CHILL --- Dwarf Planet still means Planet --- Stupid People
It's a classifaction .... you sheep can be so dumb sometimes. ...
eom
Posted by Thomas, David (1947 comments )
Reply Link Flag
I agree
Just because they relabeled Pluto to Dwarf Planet, doesn't mean it's no longer a planet.

There are regular humans and dwarf humans, does this mean a dwarf is not human? Of course not.

What they've done makes perfect sense.
Posted by Mergatroid Mania (8395 comments )
Link Flag
It's the (who say so)
Who ever has the say so, Says it &#38; it becomes So.
Posted by Earl (60 comments )
Reply Link Flag
 

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