Pluto is no longer a planet

Factual Questions
21

[QUOTE=Diceman]
From what I’ve read, only about 5% of the 10,000 or so professional astronomers worldwide actually voted on this issue. (Apparently, there was no provision for electronic voting, so you had to be physically present at the convention to vote.)
[/quote]

According to its website, the International Astronomical Union has about 8,800 individual members, of which 2,500 attended the recent General Assembly at which the resolution was passed. It is not clear exactly what the vote was (or who is eligible to vote). What is the source of your figure?

At this point, I think it’s very unlikely that Pluto will regain the status of a full planet. Whatever new definition is arrived at is pretty certain to be tailored to exclude it.

22

[QUOTE=Colibri]
At this point, I think it’s very unlikely that Pluto will regain the status of a full planet. Whatever new definition is arrived at is pretty certain to be tailored to exclude it.
[/QUOTE]

I’m not sure why you say “tailored to exclude it”.

But I don’t think there is any definition that allows our solar system to have 9 planets. However you tweak the definition, either we have a dozen or more planets (e.g. the original draft definition), or we have 8.

23

[QUOTE=scr4]
I’m not sure why you say “tailored to exclude it”.

But I don’t think there is any definition that allows our solar system to have 9 planets. However you tweak the definition, either we have a dozen or more planets (e.g. the original draft definition), or we have 8.
[/QUOTE]

Yes – if Pluto is a planet, then I don’t think there’s any possible way to exclude “Xena”, which is larger and in a similar orbital situation (except that it doesn’t orbit around the centre of mass between itself and a smaller companion). So you could write a definition which would make “Xena” a planet, but exclude Pluto, but you couldn’t go the other way round.

So how about “My very excellent mother just sent us nice xylophones”?

24

[QUOTE=scr4]
I’m not sure why you say “tailored to exclude it”.
[/QUOTE]

I think it is pretty obvious that the phrase “cleared the neighborhood of its orbit” was tacked on specifically to exclude Pluto (as well as Ceres and the other “dwarf planets.”) This seems rather artificial to me (as well as being rather unclear). Other criteria could probably also be formulated to yield just the eight major planets, but the IAU General Assembly was perhaps seeking a “quick and dirty” defintion that would avoid expanding the list of planets to 12.

It seems to me that the IAU did not want to admit more than nine planets (at least if the others are Pluto-like); as you say, the choice is either between eight and more than nine, so Pluto has to go.

25

And here’s the kicker - even the major planets haven’t “cleared the neighborhood around their orbit.” What about the trojan asteroids? The apollo asteroids? In another thread, someone said that these didn’t count since they’re in gravitational equilibrium with the planet whose orbit they share, but still, they’re there and they haven’t been cleared. Are Jupiter and Earth not planets then too?

Rather a strange definition. I agree with **Colibri’**s “tailored to exclude Pluto” idea.

26

[QUOTE=Snickers]
And here’s the kicker - even the major planets haven’t “cleared the neighborhood around their orbit.”…
[/QUOTE]
The neighborhood is a mess!

CMC fnord!

27

[QUOTE=Snickers]
What about the trojan asteroids? The apollo asteroids?
[/QUOTE]

I’d argue that they are gravitationally bound to the respective planets.

28

[QUOTE=Colibri]
According to its website, the International Astronomical Union has about 8,800 individual members, of which 2,500 attended the recent General Assembly at which the resolution was passed. It is not clear exactly what the vote was (or who is eligible to vote). What is the source of your figure?

[/QUOTE]

This story says that only about 300 attendies actually voted. An article that I can’t find now used the 500 figure, and another article says “a few hundred” voted. Unless these articles are all way off-base, the “voter turnout” was abysmally low. I suspect that the fact that you had to go to Prauge to even have the option of voting probably had a lot to do with that.

How’s this for a better solution: instead of talking about “planets” and “dwarf planets,” have the categories be “Major Planets” and “Minor Planets.” Both major and minor planets could legitimately be considered planets, but we’d still get to keep the warm fuzzy feeling that the 8 classical planets are something special. After all, they’re not just planets, they’re major planets.

Under my scheme, a planet would be any solar object that directly orbits a star, is not a star itself, and has enough gravity to pull itself into a round shape. (This is what most people have in mind when they imagine a planet, after all.) A major planet would be one that “is large enough and has sufficient gravity to have cleared (via impact, capture, or ejection) any objects in its oribal neighborhood that are within an order of magnitude of the planet’s mass.” This means, simply, that there is not else like the planet nearby. The order-of-magnitude requirement is so that small asteroids or comets won’t stop a planet from being “major,” but anything else of comparable size would. This will allow Pluto, Sedna, “Xena,” and Ceres to not qualify as major. A minor planet would, by definition, be any planet that is not gravitationally significant enough to have dealt with the competition.

While we’re at it, lets just shorten the term Kuiper Belt Objects to “Kuipers.” And lets specify that asteroids and Kuipers are small solar bodies, to settle the issue of where Ceres is simultaniously an asteroid and a dwarf/minor planet. (No.)

29

I’m wondering why we can’t just call everything that orbits a star a “planet”, and then just recognize that there are millions of them everywhere? It’s not like it matters what the hell you call something, it is still just a big rock orbiting some gigantic nuclear reactor. School kids could still be taught that there are a few big, important planets that we should remember and pay attention to, so nothing really would change on that front, except kids would realize early on that the solar system is not just nine planets and the sun.
Even in high school I knew that the only reason we called Pluto the ninth planet was because an American discovered it, we were exited, and once we figured out it really was just a minor bit of space debris it was too late. So if this definition sticks I won’t be too sad to see Pluto go. I always liked having a planet with the same name as a cartoon dog, though.

30

[QUOTE=DrCube]
I’m wondering why we can’t just call everything that orbits a star a “planet”, and then just recognize that there are millions of them everywhere?
[/QUOTE]

Did you catch the Perseid Planet Shower a couple weeks ago? Most of the planets raining down through earth’s atmosphere were the size of a grain of sand, but some were as big as your fist!

31

If you look at the ratio of masses of the primary object (alleged planet) and the masses of all other objects in the same orbital zone, there is a clear distiction

(see table 1 on page 17)

Brian