Vinnie

How many of you think pluto should be classified as a planet? If so, why?

Vinnie

fando

I don't see why classification is important. Pluto doesn't care how we label it, it's simply a chunk of ice and rock going about its merry orbiting business.

I've never understood the strong debate of celestial body classification. There is a whole continuum of masses to study and discover. Having artifical classification schemes that are strongly influenced by the nature of our solar system can only keep us from visualizing all the posibilities.

Just my 2 grams of starstuff.

Abacus

I don't think it should be classified as a planet. Even under an arbitrary classification system, the current dividing line between planet and non-planet doesn't make sense. I remember reading about ice-bodies being found farther out that are a good fraction of the size of Pluto. It wouldn't surprise me if someday one was found which was bigger. Would we classify that as a planet, or not?

I don't know if the kind of orbit it takes is a consideration, but Pluto's orbit is pretty funky. Not only is its orbit highly eccentric, but its orbital plane is tilted way off axis from the other planets (about 17 degrees from earth's orbital plane).

But I'm not an astronomer, so I probably don't know what I'm talking about.

ishalon

Why shouldn't it be?

And why are the other planets orbits' on a plane?

beausoleil

The solar system formed from a roughly spherical cloud collapsing. Because the cloud was rotating, it couldn't just collapes to a point. To conserve angular momentum it collapsed to an accretion disk, which fed material in to the central star. The planets formed in this disk - that's why they now orbit close to a common plane.

Zimyatin

A resident of Jupiter would have a laugh at us earthlings trying to kick Pluto out of the planetary club.

Abacus

Heh! Of course, everything orbiting the sun from Jupiter on down to the smallest dust particle is really nothing but a collection of debris, considering that 99% of the mass of the solar system is concentrated in the sun.

Major Billy

For one, it's too small- smaller than our Moon even. It's also made of ice, not rock like the Earth, or gaseous like the outer planets. Pluto is in fact a Kuiper Belt object, comet-like objects that have irregular orbits in the Solar System outside the planet's orbits.

ishalon

thanks, fairly simple to get (i need to do some reading on astrology)

[Edit: typo]

[ July 13, 2002: Message edited by: ishalon ]</p>

Asha'man

In the August 2002 Sky and Telescope, I read a very reasonable proposal for the definition of a planet, provided by S. Alan Stern and Harold F. Levison.

Paraphrased, the idea was to define a planet by mass alone, and proposed an upper and lower limit based on the following: The body must be low enough mass that at no time, past or present, can it generate energy in its interior due to any self-sustaining fusion reaction. The body must be massive enough that its shape is determined primarily by gravity rather than mechanical strength or other factors like surface tension or rapid rotation.

This definition seemed to make a great deal of sense to me, and allows Pluto to remain a planet. We would have to re-classify a few of the larger moons as planets as well, but that doesn’t bother me much.

An alternate definition was also suggested. Essentially, a body is a planet if it “dynamically important to the system in which it is found.” This means an object, orbiting a star, that has cleared away its neighboring planetesimals through gravitational interactions. This additional definition might allow us to make a category for things that have the mass of a planet, but are really moons orbiting a larger planet.