Astronomers Debate Status of Pluto and Xena

[VT-16]

I wish they'd expand on the moon-definition while they're at it. Some of the criticism is assosiated with the notion that if spherical objects smaller than some of the moons in our system get to be planets, they should be planets as well.

I suggest a new term for moons that fit the criteria: satellite planets.
Another distinct subdivision of the planet-term.

[General Trelane (Retired)]

I'm sorry, but anything the size of Ceres, or with the physical characteristics of Pluto is NOT a planet.

OK, I'll point out the obvious. . .Pluto currently IS classified as planet (notwithstanding those who circumvent due process and arbitrarily declare that it is not). I'm not saying that it will remain classified as a planet, but for now it is. Therefore, something with the physical characteristics of Pluto (Pluto, in this case) certainly can be a planet.

What you meant to say was, "I'm sorry, but in my opinion, anything the size of Ceres, or with the physical characteristics of Pluto should NOT be a planet." And in the process, you demonstrate the problem in this debate--everyone has their own opinion on what should and should not be a planet. Some adhere to their position with a rigid dogmatism, and no one definition will please everybody.

[GrandMasterTerwynn]

I'm sorry, but anything the size of Ceres, or with the physical characteristics of Pluto is NOT a planet.

the KBO's (including Pluto) are big comets. If you brought them close to the sun, they'd lose there mass as there surfaces melted and were blown away.

Frankly, if you brought any planet close enough to the Sun, it would lose mass as its surface vaporized and was carried away by the solar wind. This is a fairly stupid way of disqualifying a body from planethood.

As for Ceres, it's to small.

Mercury, or possible the Moon, should be the lower limit for the size of a planet, if in orbit of a star.

This is entirely arbitrary. Ceres may be small, but it's a full third the mass of the asteroid belt. Its next most massive competitors have something like a third of its mass (and it masses more than several of the next largest asteroids in the belt combined.) Ceres also massive enough to have internally differentiated, so it has a crust, a mantle (albeit an icy one,) and a rocky core.

If we're going to start making arbitrary definitions, we should at least have them make some sort of geological sense. And, as irksome and unromantic as it may be, the proposed definition does make a certain amount of sense. Now mind you, Ceres just barely sneaks in as it happens to share space with a lot of other bodies, but it's a Doberman in a pack of chihuahuas.

[drachefly]

Around a tiny Red Dwarf, certain objects would be large enough to clear other objects out of their orbits, yet be too small to become spheres.

Should such objects be planets?

Even the most feeble red dwarf stars will have an appreciable fraction of Sol's mass. There's nothing that would prevent them from forming planetary systems with objects that would be satisfactorily spheroid planets of significant size.

Suppose it was formed in a low-metal region. Suppose it was first-and-a-half generation. Not much rock around, but some.

[GrandMasterTerwynn]

Around a tiny Red Dwarf, certain objects would be large enough to clear other objects out of their orbits, yet be too small to become spheres.

Should such objects be planets?

Even the most feeble red dwarf stars will have an appreciable fraction of Sol's mass. There's nothing that would prevent them from forming planetary systems with objects that would be satisfactorily spheroid planets of significant size.

Suppose it was formed in a low-metal region. Suppose it was first-and-a-half generation. Not much rock around, but some.

Then you could probably end up with a gas giant, like the oldest known extrasolar planet which formed nary a billion years after the universe started. And unless you had an incredibly sparse dust disc surrounding the newly born red dwarf, even a metal-poor planetary system should form worlds like Ceres, the icy/rocky moons of Jupiter and Saturn, or even Vesta-like bodies. All of which are certainly large enough to form spheres and possibly undergo internal differentiation. And, I suspect, you can't have too sparse a dust disc. Too little material, and it's arguable it would be blown off into interstellar space by the new star's stellar wind, before it had a chance to form more than scattered debris.

[drachefly]

Ah, but would they sweep their region clean?

[CaptainChewbacca]

I'm betting that in the future the solar system will be classified into "Major Planets" and "Minor Planets".

It would be fine for me.

[Lord Zentei]

I'm betting that in the future the solar system will be classified into "Major Planets" and "Minor Planets".

It would be fine for me.

As long as someone can define what the definition of "minor" and "major" is.

[CaptainChewbacca]

Probably the "inner 8" planets, though some might want to cut out mercury. For that, you could just do a straight size-line.

[Lord Zentei]

Probably the "inner 8" planets, though some might want to cut out mercury. For that, you could just do a straight size-line.

Mercury is a hell of a lot bigger than Pluto, Xena or Charon. Combined.

[General Trelane (Retired)]

. . .Ceres just barely sneaks in as it happens to share space with a lot of other bodies, but it's a Doberman in a pack of chihuahuas.

Perhaps we should rename it Cerberus!

[GrandMasterTerwynn]

. . .Ceres just barely sneaks in as it happens to share space with a lot of other bodies, but it's a Doberman in a pack of chihuahuas.

Perhaps we should rename it Cerberus!

Nope, that name is already taken.

[Molyneux]

Probably the "inner 8" planets, though some might want to cut out mercury. For that, you could just do a straight size-line.

Umm...don't you mean "Inner 9", unless you want to exclude Neptune? Ceres is smack-dab between Mars and Jupiter.

[McC]

Also, we would officially have a planet "Xena" and I don't know if I want to give Sam Raimi that kind of power.

This is from the locked thread on this topic, but I wanted to respond to it. Xena is not an official name -- this body has not yet been given an official name. The article you posted says as much:

Brown dubbed the body Xena after the television series about a warrior princess, but it is officially known as ``2003 UB313," and has not been given a permanent name.

[CaptainChewbacca]

Thank God. I was afraid it was official.

[General Trelane (Retired)]

. . .Ceres just barely sneaks in as it happens to share space with a lot of other bodies, but it's a Doberman in a pack of chihuahuas.

Perhaps we should rename it Cerberus!

Nope, that name is already taken.

I'll avoid replying like Count Floyd (who had to explain his "Have a Nice Day" bumper-sticker joke).

[Molyneux]

. . .Ceres just barely sneaks in as it happens to share space with a lot of other bodies, but it's a Doberman in a pack of chihuahuas.

Perhaps we should rename it Cerberus!

Nope, that name is already taken.

Ceberus, then?

[Mange]

Space.com writes that a counter proposal has been put forward which would demote Pluto to a non-planet status (or a "dwarf planet"). This new proposal seems, imho, to be quite ambigous. Article at Space.com.