12 Planets

[den]

Congratulations Pluto for being confirmed into the Planet club! And congrats to Charon, UB313 and Ceres on your promotions!

HOORAY!

Comments

[the-gneech.livejournal.com]

Except I thought that Charon orbited Pluto, which would make it a moon.

-The Gneech

[nekura-ca.livejournal.com]

Actually, because of Pluto and Charon's relative sizes, they orbit a common barycenter (http://en.wikipedia.org/wiki/Center_of_mass#Barycenter) point outside of both planets, so neither one really orbits around the other. It's been reclassified as a double planet system, which I think is really neat.

[(Anonymous)]

So Pluto and Charon are more like a bola than a yo-yo. That makes sense.

[nekura-ca.livejournal.com]

Yeay, cogratulations *throws confetti*

It's about time they got around to finally deciding on the status of all the new objects they've been finding. I like the definition that they have, although I can see some problems with it.

My thinking is, anything large enough to have other objects orbiting it is more then just another chunck of rock. I'm interested to see what happens with EL61.

I'm also very happy that "Xena" is not on the list of names submitted for consideration for the official name of UB313.

[dewhitton.livejournal.com]

I think Xena should be on a list of prohibited names or something.

EL61 will be interesting to classify.

[http://users.livejournal.com/crossfire_/]

The proposal hasn't been ratified yet (IIRC, the official vote is on the 24th). There's a great deal of politicking about this particular issue; people feel very strongly about it.

I haven't quite decided where I stand on the issue. My instinct is that we need to trash the word "planet" and come up with new and different words to describe the various things out there, but I know that'll never happen.

[dewhitton.livejournal.com]

I think the word came from Greek, meaning "Wanderer" and was used to refer to the plantes visible before Telescopes were invented. By that definition, Saturn is the furthest-most planet; everything else is not visible to the unaided eye.

[lostwanderfound.livejournal.com]

My thinking is, anything large enough to have other objects orbiting it is more then just another chunck of rock.

It's not really significant from a definitional point of view. Quite a lot of comets and other small thingies have bodies orbiting them (to at least the same degree that Charon "orbits" Pluto; ie, barycenter above the surface), and there's no real reason why we can't have a planet without any satellites.

The definition they appear to be going with is that anything massive enough to be pulled into a globular form (at least roughly) by its own gravity gets called a planet, unless it's big enough to drive fusion, in which case it's a star.

(this makes small Brown Dwarfs the remaining categorisation problem: big planets, small stars, or a category all their own?)

Incidentally, it seems likely that one of the major factors in not kicking Pluto completely out of the planet category was political, not scientific: it's easier to get research funding to investigate a planet than it is to investigate a "Trans-Neptunian Object".

[nekura-ca.livejournal.com]

I was just thinking that as a sufficient condition, rather then a necessary condition. It doesn't rule out moonless planets. I was thinking if an object has a strong enough gravity field to hold a stable moon within it's Hill Sphere, it's more then a small asteroid.

Cometary debris clouds are not stable, and are either blown off, creating the tail, or fall back to the surface as the comet heads back to the outer solar system.

The definition also includes the condition that it's orbiting a star, so brown dwarfs are still "up in the air" as it were ^_^

That, and it's a lot easier to change the definition, then to admit that they've be wrongly calling it a planet for the past 75 years.

[starcat-jewel.livejournal.com]

You are correct. The classical planets (which include the sun and the moon) are called that because they "wander" across the sky against the background of fixed stars.

[torakiyoshi.livejournal.com]

I hope the planets dont have abola! Imagine, the first fatally diseased planets... yipes!

Congrats to Pluto, and thanks for the link, Batty!

Have teh best

-=TK, space geek

[torakiyoshi.livejournal.com]

Do you read 365 Tomorrows? Check out this... rather unfortunate... prediction of the future (http://www.365tomorrows.com/08/15/the-mythical-princess/). Can you figure out who the 20th Century princess is?

Have teh best

-=TK

[nekura-ca.livejournal.com]

Ok, after finding this list of asteroids with satellites (http://www.johnstonsarchive.net/astro/asteroidmoons.html), I guess it's a little more common then I thought. Interesting stuff. Obviously it's not sufficient ^_^

[acelightning.livejournal.com]

[lostwanderfound.livejournal.com]

Oh, and also (obviously), has to not be a moon, which thanks to Charon, now appears to mean: globular object orbiting a planet with a barycenter below the surface.