But it can pretend to be a planet!*

[astra_nomer]

I've been getting kind of tired about all the news stories about thousands of astronomers meeting in Prague to determine whether or not Pluto is a planet, as if that's the only thing that will happen at the IAU meeting this week. So it's kind of a relief to hear what the actual news is, which is that the IAU is proposing to create a new class of planet, "dwarf" planets as they've been dubbed by the media.

To summarize, there would be the 8 "classical" planets.

The dwarf planets would include Pluto, Ceres (the largest asteroid), 2003 UB₃₁₃ (Xena), and Charon (Pluto's moon). Furthermore, there would be a class of object called plutons that include all of the above except asteroids.

Except there's already a name for the class of objects that characterize plutons, which is "Kuiper Belt objects." Is is just an issue of size in that case?

What about the Earth's moon and the Galilean satellites, which are all bigger than Pluto?

Really, I think the only people who care about planet nomenclature are schoolchildren and Michael Brown, the discoverer of 2003 UB₃₁₃, who would much rather be known for discovering a planet rather than a large Kuiper Belt object.

I think this quote by Geoff Marcy sums up my own attitude quite nicely:

“I am not attending the I.A.U. meeting, nor do I care about the outcome of any vote about whether Pluto and Xena are ‘planets.’ ”

*This is what DS1 would tell you about Pluto if you asked him about it, prefaced by the statement, "Pluto is a Kuiper Belt Object."

Comments

[jamess-fox.livejournal.com]

Ceres is not a pluton, or a Kuiper belt object. As for Charon, the reason they're putting it in is that the barycenter of the Pluto-Charon system lies outside Pluto, thus, they argue, Pluto and Charon are 'double planets', rather than Pluto being the planet and Charon the moon.

[chenoameg.livejournal.com]

I think they just need to get us excited about Kuiper Belt Objects, and we can start naming all of them, so that will make everyone happy.

More planets, bah.

[rms10.livejournal.com]

I'm really unhappy with including Ceres and the KBOs into one category of dwarf planets. Composition should play a role in the categorization, and not just size.

I like promoting Charon, though, since the center of gravity of the Pluto-Charon system is actually between them. Calling Charon a moon is not quite accurate there.

[firstfrost.livejournal.com]

People who study Pluto also care about whether Pluto is officially a planet or not. :)

[gigglefest.livejournal.com]

* aww, that's all cute and impressive! I guess I shouldn't be surprised, but still.

[marcusmarcusrc.livejournal.com]

I note Michael Brown has an op-ed in the nytimes. 3/4 of the op-ed sounds very reasonable, and seems to be an argument for "Yeah, Pluto might not be a real planet, but heck, maybe Australia isn't a real continent either (or maybe Greenland should be), and we just let some things be because it was that way historically."

Then he ends his op-ed by talking about how 2003 UB313 should totally be a planet, but not any of these other posers, thereby totally undermining the rest of his argument.

(To be honest, I've always kind of felt like gas giants and rocky planets should be split into two separate categories, but I guess that's a totally different discussion)

[arcanology.livejournal.com]

A good spanking for everyone who actually cares will sort this thing right out.

[visage.livejournal.com]

So, is there a non-arbitrary definition that'd include the 8 and exclude the rest?

"Pluto and Charon are a double planet because the center of mass is between them" would mean that Earth/Luna is a double planet system as well, right? (Earth's approximately 100 times more massive than the moon; the distance between the earth and moon is approximately 400 times the earth's radius. Assuming I've got my numbers right...)