'Yes, Pluto Is a Planet' (sfgate.com)

schwit1 quotes a Washington Post perspective piece by the authors of a new book about Pluto: The process for redefining planet was deeply flawed and widely criticized even by those who accepted the outcome. At the 2006 IAU conference, which was held in Prague, the few scientists remaining at the very end of the week-long meeting (less than 4 percent of the world's astronomers and even a smaller percentage of the world's planetary scientists) ratified a hastily drawn definition that contains obvious flaws. For one thing, it defines a planet as an object orbiting around our sun -- thereby disqualifying the planets around other stars, ignoring the exoplanet revolution, and decreeing that essentially all the planets in the universe are not, in fact, planets.

Even within our solar system, the IAU scientists defined "planet" in a strange way, declaring that if an orbiting world has "cleared its zone," or thrown its weight around enough to eject all other nearby objects, it is a planet. Otherwise it is not. This criterion is imprecise and leaves many borderline cases, but what's worse is that they chose a definition that discounts the actual physical properties of a potential planet, electing instead to define "planet" in terms of the other objects that are -- or are not -- orbiting nearby. This leads to many bizarre and absurd conclusions. For example, it would mean that Earth was not a planet for its first 500 million years of history, because it orbited among a swarm of debris until that time, and also that if you took Earth today and moved it somewhere else, say out to the asteroid belt, it would cease being a planet.

To add insult to injury, they amended their convoluted definition with the vindictive and linguistically paradoxical statement that "a dwarf planet is not a planet." This seemingly served no purpose but to satisfy those motivated by a desire -- for whatever reason -- to ensure that Pluto was "demoted" by the new definition. By and large, astronomers ignore the new definition of "planet" every time they discuss all of the exciting discoveries of planets orbiting other stars.

Comments

What about Neptune

[meerling]

Pluto and it's moons are a pretty significant set of objects, and they cross Neptunes orbit, so does that mean Neptune is no longer a planet since it sure as heck hasn't "cleared it's zone" ?

Re:Yes, that was actually the point

[Solandri]

The IAU isn't an official body with any authority other than what they have taken on themselves. And if they are going to let historical politics cloud scientific thinking, they certainly aren't going to speak for me. I'd like to see some textbook publishers take a stand too.

The thing is, if you don't accept the IAU's authority, then whose authority are you going to accept? Textbook publishers? They're one notch above those scammers who sell you the "right" to name a star.

The IAU's membership is over 12,000 professional astronomers, which as best as I can tell is a pretty good percentage of the people with careers in astronomy. The next largest professional group is the American Astronomical Society, with about 7,000 members all in the Americas. Their stance on the issue is decidedly neutral.

In the end, the definition of a planet is merely semantics. What's important is that whatever definition you decide to use is functional, allowing generalized statements to be made easily without running afoul of the terminology. In that respect, I don't have a problem with the division between "planet" and "trans-Neptunian object" and dwarf planet. They are different enough and the terms selected for them, although not perfect, are definitive enough to make statements and issue papers about them without tripping over the semantics.

*shrug*

[aepervius]

The classification does not change anything truly, but frankly the IAU kerfuffel DOES have a point : People want to keep Pluto out of sentiment. When you point them there is then more than 100 planet to add if Pluto is a planet, THEN they go back to the "but-this-is-what-i-learnt" BS defense. The IAU definition might not be 100% good, but some of the objection to it are stupid. Like the one it does not apply to other solar system. That one is frankly stupid , change the grammar to "its star" and bam, problem solved (and frankly when I read the definition the first time I read it that way too). I think that simply a lot of people cannot emotionally let go of that pluto-named TNO and will do anything including CT about not giving credit. Pretty much avoid recognizing that Pluto as a planet was pretty damn only an accident due to detection as opposed to a real definition. Just looking at the ecliptic should give IMO a hint.