posted
I just heard a report on the radio that said they'd decided, rather than to exclude Pluto, to be more inclusive. So the official definition of a planet (put loosely, one with sufficient gravity to be round) now allows for Pluto. . . And Xena. . . And Ceres. . . And, also, bizarrely, Charon (Pluto's moon). Surely the definition should exclude planets not actually in orbvit around the sun?
So, fear not, we're not down to eight planets, we're up to twelve. With more on the way. We've gone from living in the Mirror Universe, to living in the Firefly 'verse!
(I tried to find a news report online, but all I found was that Bruno Kirby has just died of Leukaemia. That's sad. Perhaps they should name a planet after him)
posted
This is just the proposal for the definition. It hasn't been voted on just yet, but seeing as its the only proposal, I'd wager it's just a matter of time.
quote:From the IAU website: A planet is a celestial body that (a) has sufficient mass for its self-gravity to overcome rigid body forces so that it assumes a hydrostatic equilibrium (nearly round) shape, and (b) is in orbit around a star, and is neither a star nor a satellite of a planet.
However, in all of ten seconds, I have discovered a fatal flaw in this definition.
quote:From the IAU website: For two or more objects comprising a multiple object system, the primary object is designated a planet if it independently satisfies the conditions above. A secondary object satisfying these conditions is also designated a planet if the system barycentre resides outside the primary. Secondary objects not satisfying these criteria are "satellites". Under this definition, Pluto's companion Charon is a planet, making Pluto-Charon a double planet.
Ergo, because the Pluto-Charon center-of-mass lies outside Pluto, Charon technically orbits the Sun.
Now follow this logic:
The Sun-Jupiter center-of-mass lies outside the Sun. Therefore, Jupiter does not orbit the Sun. Therefore, Jupiter is not a planet.
Discuss.
-------------------- "Kirito? I killed a thing and now it says I have XPs! Is that bad? Am I dying?"
-Asuna, Episode 2, Sword Art Online Abridged
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Cartman
just made by the Presbyterian Church
Member # 256
posted
Pluto (the primary) satisfies A and B, so is called a planet.
Charon (the secondary) satisfies A, but not B, yet is designated as if it also satisfies B because of extra condition C, so is called a planet as well.
Thus we have the weird definition that a planet is any object for which the expression (A && (B || C)) or equivalently ((A && B) || (A && C)) [where the second operand is obviously out of place] evaluates to true. Someone at the IAU needs a course in basic propositional logic...
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Cartman
just made by the Presbyterian Church
Member # 256
posted
You know, I think what the IAU definition is supposed to imply is that it depends on how you define the "primary" and "secondary" objects in a system. The primary gets called a planet if (A && B) is true, but the secondary only if ((A && B) && C) is true, if I'm interpreting "a secondary object satisfying these conditions is also designated a planet if the system barycentre resides outside the primary" right. But by that logic, Charon shouldn't be a planet, while the IAU says it is in the same passage... ARGH.
-------------------- ".mirrorS arE morE fuN thaN televisioN" - TEH PNIK FLAMIGNO
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posted
You're right. Charon (the secondary) does not satisfy these conditions, because it is not in orbit around a star (condition B). But perhaps what they mean is that Charon ISN'T in orbit around Pluto, they're both orbiting around a point in space (the barycentre).
posted
And, to add further brilliance - this idea, that a planet needn't orbit the sun per se but could join similar planets in orbiting around a central point/external barycentre (which itself orbits the sun) makes the multi-planet system in Firefly a lot more possible! I'd like to see Balaam have another crack at his 'verse map in these terms. . .
posted
Meh, the only reason that Charon isn't orbiting Pluto entirely is because Pluto is too damn small to hold its own position. The reason they both orbit a barycenter is probably because Pluto got knocked out of position when it captured Charon.
THEY'RE ALL JUST DAMN PLANETOIDS, DAMMIT!
-------------------- “Those people who think they know everything are a great annoyance to those of us who do.” — Isaac Asimov Star Trek Minutiae | Memory Alpha
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quote:Originally posted by MinutiaeMan: Meh, the only reason that Charon isn't orbiting Pluto entirely is because Pluto is too damn small to hold its own position. The reason they both orbit a barycenter is probably because Pluto got knocked out of position when it captured Charon.
Incorrect. The barycenter is just a fancy way of saying "center-of-gravity". The barycenter is outside of Pluto because Pluto isn't much bigger than Charon.
Which brings me back to my point: If Charon is now considered a planet because the Pluto-Charon barycenter is outside Pluto, shouldn't Jupiter be considered, uh, something else because the Sun-Jupiter barycenter is outside the Sun?
-------------------- "Kirito? I killed a thing and now it says I have XPs! Is that bad? Am I dying?"
-Asuna, Episode 2, Sword Art Online Abridged
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posted
Interesting side note - Ceres was originally called a planet after its discovery in 1801 until about 1850. What caused astronomers to change their minds was simply the discovery of more asteroids� a lot more.
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posted
Yipe! Did anyone notice on this page (last question at the bottom) that if this passes as-is, we would have 12 planets to start with, and possibly 24 total that we know of today? Those last 12 aren't being immediately passed (several are larger than Ceres) I think because we don't yet know enough about them to be sure.
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posted
Yep. Pluto was called a planet because they thought it was unique. Now it's obviously not unique. But now, astronomers seem to be going in the opposite direction.
I have to say I'm disappointed and annoyed, but not surprised, to see the IAU trying to keep Pluto's status as a planet. I'm just really shocked they want to consider Ceres a planet again, too. That's just crazy talk!
My dad asked an interesting rhetorical question as an analogy for this issue: "Just what marks the difference between a child and an adult?"
Also, to all those nutcases who want to keep Pluto as a planet because it's the only planet discovered by an American, I'd like to point out that Oog the Caveman, who lived in the vicinity of Nome, Alaska, was actually the first to notice the planet we now call Mars. Except that he called it Oogaboog.
-------------------- “Those people who think they know everything are a great annoyance to those of us who do.” — Isaac Asimov Star Trek Minutiae | Memory Alpha
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Shik
Starship database: completed; History of Starfleet: done; website: probably never
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posted
Personally, I've always considered Pluto & Charon to be trojan planets. But I'm weird.
if I were on the naming board for the IAU, I would totally submit names from Firefly.
-------------------- "The French have a saying: 'mise en place'—keep everything in its fucking place!"
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quote:Originally posted by MinutiaeMan: I have to say I'm disappointed and annoyed, but not surprised, to see the IAU trying to keep Pluto's status as a planet. I'm just really shocked they want to consider Ceres a planet again, too. That's just crazy talk!
I think you've summed up my position pretty well, too. I was really expecting that they would adopt the first of the three suggestions, that would make everything bigger than Pluto a planet, so that we would have a total of ten right now. But I never imagined that they'd go with the second suggestion (the "roundness" one)! Take it from me, I'm a science teacher! Kids can't even remember nine planets, let alone dozens!
-------------------- "Kirito? I killed a thing and now it says I have XPs! Is that bad? Am I dying?"
-Asuna, Episode 2, Sword Art Online Abridged
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