[SunkenCiv]

"To Pluto And Far Beyond" By David H. Levy, Parade, January 15, 2006 -- We don't have a dictionary definition yet that includes all the contingencies. In the wake of the new discovery, however, the International Astronomical Union has set up a group to develop a workable definition of planet. For our part, in consultation with several experienced planetary astronomers, Parade offers this definition: A planet is a body large enough that, when it formed, it condensed under its own gravity to be shaped like a sphere. It orbits a star directly and is not a moon of another planet.

[SunkenCiv]

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IAU definition of planet:

The definition of “planet” set in 2006 by the International Astronomical Union (IAU) states that in the Solar System a planet is a celestial body that:

1. is in orbit around the Sun,
2. has sufficient mass to assume hydrostatic equilibrium (a nearly round shape), and
3. has “cleared the neighbourhood” around its orbit.

A non-satellite body fulfilling only the first two of these criteria is classified as a “dwarf planet”, which is not a type of planet, while a non-satellite body fulfilling only the first criterion is termed a “small solar system body” (SSSB). Initial drafts planned to include dwarf planets as a subcategory of planets, but because this could potentially have led to the addition of several dozens of planets in the Solar System, this draft was eventually dropped. In 2006, it would only have led to the addition of three (Ceres, Eris and Makemake) and the reclassification of one (Pluto). The definition was a controversial one and has drawn both support and criticism from different astronomers, but has remained in use.

According to the definition, there are currently eight planets and five dwarf planets known in the Solar System. The definition distinguishes planets from smaller bodies and is not useful outside the Solar System, where smaller bodies cannot be found yet. Extrasolar planets, or exoplanets, are covered separately under a complementary 2003 draft guideline for the definition of planets, which distinguishes them from dwarf stars, which are larger.

Reasons for the debate:
Before the discoveries of the early 21st century, astronomers had no real need for a formal definition for planets. With the discovery of Pluto in 1930, astronomers considered the solar system to have nine planets, along with thousands of smaller bodies such as asteroids and comets. Pluto was thought to be larger than Mercury.

In 1978, the discovery of Pluto’s moon Charon radically changed this picture. By measuring Charon’s orbital period, astronomers could accurately calculate Pluto’s mass for the first time, which they found to be much smaller than expected.[1] Pluto’s mass was roughly one twentieth of Mercury’s, making it by far the smallest planet, smaller even than the Earth’s Moon, although it was still over ten times as massive as the largest asteroid, Ceres.

In the 1990s, astronomers began finding other objects at least as far away as Pluto, now known as Kuiper Belt Objects, or KBOs.[2] Many of these shared some of Pluto’s key orbital characteristics and are now called plutinos. Pluto came to be seen as the largest member of a new class of objects, and some astronomers stopped referring to Pluto as a planet.[3] Pluto’s eccentric and inclined orbit, while very unusual for a planet, fits in well with the other KBOs. New York City’s newly renovated Hayden Planetarium did not include Pluto in its exhibit of the planets when it reopened as the Rose Center for Earth and Space in 2000.[4]

Starting in 2000, with the discovery of at least three bodies (Quaoar, Sedna, and Eris) all comparable to Pluto in terms of size and orbit, it became clear that either they all had to be called planets or Pluto would have to be reclassified. Astronomers also knew that more objects as large as Pluto would be discovered, and the number of planets would start growing quickly. They were also concerned about the classification of planets in other solar systems. In 2006, the matter came to a head with the measurement of the size of 2003 UB313. Eris (as it is now known) turned out to be slightly larger than Pluto, and so was thought to be equally deserving of the status of ‘planet’.[3]

http://en.wikipedia.org/wiki/2006_definition_of_planet

[b4its2late]

I vote it is.

[Lucius Cornelius Sulla]

That definition would include Pluto plus one or more other members of the Oort cloud plus Ceres in the Asteroid Belt, making for 11 or more Solar planets.

[Lancey Howard]

No, Pluto is a dog.

[GregoTX]

Someone is claiming they have obtained Plutos Birth Certificate, and it says Pluto is a planet.

[Zeppo]

It certainly is, that is if the Plutonian delegation to the IAU has any say in the matter...

[Billthedrill]

Heck, I dunno, but probably not. I mean, Pluto goes around the Earth just like the Sun does, and we don’t think of the Sun as a planet. ;-)

[BuffaloJack]

PLUTO is a planet!
It always has been and always will be.
No group of liberal dweebs can change that.

[Conan the Librarian]

A Rose by any other name is still a rose. Does it matter what we call the comet-like object called Pluto?

Not really. Pluto is still a comet, and member of the Kuiper belt, even if decide to call it a planet.

I suggest ‘The Pluto Files’ by Neil Degrasse Tyson.

He puts the whole argument into plain English.

If Pluto was anything other than an inanimate object, the name may matter to it. But, it’s a snowball in space. It has no feelings. Most people couldn’t find it in the sky, even if they had a telescope big enough to see it.

It’s the same thing as Hubble. We are so busy fawning over Hubble like it is a living thing, that we waste time and money and risk the lives of astronauts trying to keep it in space, instead of putting up the next generation of telescope already and letting that hunk of space junk just finally burn up.

[wildbill]

Everyone knows he’s Mickey’s dog. Has the scientific world gone mad?

[SunkenCiv]

Was the Pluto Vote Anti-American?
by Robert Naeye
Sky & Telescope
September 5, 2006

The short answer to this potentially explosive question is "I don't know." ...While there is no proof for the accusation in the title above, three leading American planetary scientists told me last week that they keenly sensed a strong anti-American component in the IAU vote... These astronomers, who do not wish to be named for fear of backlash, charge that at least some of the astronomers used the Pluto vote as a way to "stick it" to the United States for its perceived domination of the IAU in past years, and to protest the invasion of Iraq... In going against the DPS endorsement, the IAU essentially delivered a slap in the face to the largest organization of planetary sciences in the world -- whose membership happens to be predominantly American. A petition that circulated last week among a partial list of DPS members, and which calls for a revised definition of "planet," attracted more than 300 signatures. But I was struck by the fact that only a handful came from scientists outside the US. Regardless of what one thinks of Pluto, the wording (and not necessarily the intent) of the IAU's accepted definition is deeply flawed, as I pointed out in my blog entry on August 24th. It boggles my mind that hundreds of intelligent, well-informed astronomers actually voted for it. It deliberately excludes extrasolar planets, and because it specifies that a planet is a celestial body that "has cleared the neighborhood around its orbit," a literal interpretation would boot out Earth, Mars, Jupiter, and Neptune.

[Brett66]

Apparently Pluto was demoted based on the 3rd criteria:

3. has “cleared the neighbourhood” around its orbit.

But maybe Neptune should be demoted, after all, it didn’t “clear the neighborhood” of Pluto.

Pretty silly and arbitrary, I always thought they should set a diameter limit at Pluto’s diameter and classify anything equal or larger than that a planet.

This would give them a clear definition instead of a silly “cleared the neighborhood” criteria.