August 16, 2006
12 planets.
They didn't want to hurt the feelings of Pluto-lovers, so they picked a definition for planet that would include Pluto, and, doing that, they let in 3 more rocks. The nonconformingly named 2003 UB313 (AKA Xena). Charon, which is a moon, which is annoying. And Ceres, ceresly. Wouldn't it have been pleasanter to just oust Pluto? Come on, scientists! If you want to make us feel good, make us feel good!
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27 comments:
If Charon gets to be a planet, why not Titan (bigger than Mercury or Pluto) or Ganymede? And if Ceres, why not Juno or Pallas? They're big asteroids too. This makes no sense!
Charon gets to be a planet because it does not revolve around Pluto, exactly. The two of them are a binary system, and both revolve around a center of mass that exists outside either body.
Because the center of gravity of the Titan/Saturn system is below Saturn's surface. The article mentions that this disqualies the moon.
And Ceres, ceresly.
Ann, you're a wag.
Dorothy Paker got nuthin' on you.
If they're including asteroids, then I vote for B612. Three active volcanoes, a rose, and a baobab tree it has a lot more going for it than Pluto.
Public relations. It's easier to get into the newspapers when you discover a planet in another solar system than if you discover a rock in another solar system.
"They didn't want to hurt the feelings of Pluto-lovers"
Damned degenerate Pluto-lovers, it's about time we locked 'em all up.
"Wouldn't it have been pleasanter to just oust Pluto?"
But what about Mickey and Goofy?
... sorry, couldn't resist...
I note that in the case of Ceres, it's not a promotion, it's a restoration. Ceres was considered a planet when first discovered and named.
I find the barycenter-under-surface-of-a-planet restriction unsatisfying. The reason is Jupiter -- the Sun-Jupiter barycenter is above the surface of the Sun. Logically applying the rule, then, would make Jupiter a Sun-level body in the Solar SYstem, not a planet-level body (for the same reasons the rule moves Charon from moon to planet).
In which case, there'd be 11 Solar planets, and four Jovian planets, the Solar-Jovian System.
Wouldn't it have just made a great deal more sense to just leave well alone? "Scientists debate Plutos planetary status; cancer still not cured." The very fact they're debating such a bizarre non-question suggests that there is fat to be trimmed from the astronomy department's budget.
Steven,
They did discount stars as candidates for planets, but good grab on how arbitrary the new set of rules would be under this proposal.
As a former astrophysics student, I wrote up my own feelings on this mess here, if anyone wants to get a rambling response to this ridiculous waste of researchers' time.
Dave Shuler wrote: Public relations. It's easier to get into the newspapers when you discover a planet in another solar system than if you discover a rock in another solar system.
FYI: Extra-solar planets that have been discovered are big, usually in the Jovian class. There is no debate about those planets, or their status. In fact, their immense size is that reason they can be discovered at all.
Steven wrote: I find the barycenter-under-surface-of-a-planet restriction unsatisfying. The reason is Jupiter -- the Sun-Jupiter barycenter is above the surface of the Sun. Logically applying the rule, then, would make Jupiter a Sun-level body in the Solar SYstem, not a planet-level body (for the same reasons the rule moves Charon from moon to planet).
No, Jupiter would not be a 'Sun-level' body, because it is not a star - no fusion at work in the core, and none in the past, either.
Simon wrote: Wouldn't it have just made a great deal more sense to just leave well alone? "Scientists debate Plutos planetary status; cancer still not cured." The very fact they're debating such a bizarre non-question suggests that there is fat to be trimmed from the astronomy department's budget.
No, it does not make more sense to leave well enough alone. The definition of "planet" has been poor ever since Galileo turned his telescope towards Juptier and discovered that it had satellites. I'm not sure that this new definition is terribly good (the 800K diameter and 1/12,000 the Earth's mass sound somewhat arbitrary), but some standardization of the definition would be very helpful.
As for the snide comment that "Scientists debate Plutos planetary status; cancer still not cured", I offer an even more snide comment. If your knowledge of science leads you to think that astronomers are (or should be) the folks working on a cancer cure, then perhaps you should take a few remedial classes on several subjects before offering an opinion on the budgets of astronomy departments.
JoeSchmoe, I read your proposed guidelines and it seems you're really hanging onto the gaseous atmosphere idea, saying that Pluto would still be included as a planet. According to these guys, it's not clear that Pluto has a gaseous atmosphere at all, although there is a lot of water ice present. In addition, saying that Mercury "supports" a gaseous atmosphere is also kind of a stretch.
I don't have a problem with the new guidelines per se. I am amused at the minor hissy fits this will cause, though -- lots of mnemonics will have to be updated, and a lot of kids' educational shows will become instantly wrong. I will be a little sad if the Blue's Clues Planet Song has to be retired... even my 4th-grader still hums it occasionally when asked to list all the planets in order.
Hey Joan,
Yeah, Mercury has what we call an exosphere, where the atoms never collide, so, by "definition" it's a gas. I told you I hate this stuff. I also think that we should boot Pluto straight out of there because it's orbit isn't even in the orbital plane of the solar system, which is why it's sometimes closer to the sun than Neptune. We used to think it was a captured comet, but, the planetologist should be the ones deciding what's a planet, not this ad hoc committee that's making all members vote on the question of new bodies being planets or not.
Hey, these guys are 'super serial' about this. And, icepick, don't some astronomers and/or astrophysicists regard Jupiter as a failed 'proto-star' or something like that? I.e., if it had been a bit bigger it would have ignited?
Icepick said...
"Simon wrote: 'Wouldn't it have just made a great deal more sense to just leave well alone?'
No, it does not make more sense to leave well enough alone. The definition of "planet" has been poor ever since Galileo turned his telescope towards Juptier and discovered that it had satellites."
The mere fact that the definition of what a planet is may well have been fuzzy for several hundred years, and perhaps that might suffice as an argument against naming a new body as a planet, but in no event does it rise to the level needed to displace - or even disturb - an understanding followed and widely understood since 1930. There are nine planets in this system, Pluto being one of them; if astronomers wish to change their criterion for subsequent admissions to that class, then they are more than welcome to do so.
Jorg:
Jupiter has been compared to a brown dwarf, but it's mass is (probably) too low to be classified as such. However, it is massive enough that it radiates more light energy (especially in the radio, microwave, and infrared wavelengths) than it receives from the sun. So, not a brown dwarf, although it's as big as one, but still a radiating body. Have I told you how much I hate this stuff?
While the barycenter of the Earth-Moon system currently lies about 900 miles beneath the surface of the Earth, tidal forces cause the Moon to slowly move away from the Earth, by a few centimeters per year. So in a few billion years the barycenter will rise above the Earth's surface, and the Moon will be promoted to planethood. Imagine the celebrations!
Gordie: Mickey is a mouse, Donald is a duck, Pluto is a dog. What's Goofy...?
Teddy: He's a dog, he's definitely a dog...
Chris: He can't be a dog, he wears a hat and drives a car...
Vern: Yeah, that is weird. What the hell is Goofy?
The mere fact that the definition of what a planet is may well have been fuzzy for several hundred years, and perhaps that might suffice as an argument against naming a new body as a planet, but in no event does it rise to the level needed to displace - or even disturb - an understanding followed and widely understood since 1930. There are nine planets in this system, Pluto being one of them; if astronomers wish to change their criterion for subsequent admissions to that class, then they are more than welcome to do so.
So Pluto is a planet because everybody says so? Brilliant.
"What's the definition of a planet?"
"A planet is any of nine celestial bodies that circle the Sun."
"Do only nine celestial bodies circle the sun?"
"No."
"Then what are the other things called?"
"Moons, asteroids, comets."
"So what makes them different than planets? Are they smaller than planets?"
"No, some of them are bigger than planets."
"Are they shaped differently than planets?"
"Some of them, but many have the same roughly sperical shape as a planet."
"Well then, do they go around the Sun in triangular patterns or something?"
"Not really, no."
"So why are planets planets, and not comets, asteroids, moons or whatnot?"
"Because everybody says they are planets."
"Why does everyone call them planets?"
... long pause ...
"Ours go up to nine...."
Astronomy, as taught by Nigel Tufnel....
"... 2003 UB313 (AKA Xena),..."
Cool, a planet for we fans of the Xena: Warrior Princess" show!
Jupiter . . . is not a star - no fusion at work in the core, and none in the past, either.
Right. But size and orbit are independent variables, and while it's not size-wise a star, it is orbit-wise an equal of the Sun in the same sense that, orbit-wise, Charon is an equal of Pluto.
Take two sets of variables.
The first is size of body, and that would give you a breakdown of stars (big enough for fusion), "middelos" (big enough to be gravitationally spheroidal), and "tinyos" (the rest of the stuff).
The second is "orbital barycenters", and the definitions would seem to be
Category 1: "none inside anything"; Category 2: "inside an object that itself belongs to the first category";
Category 3: "inside an object that itself belongs to the second category";
Category N: "inside an object that itself belongs to the N-1th category".
Under the proposed definition of "planet", it reduces to "middelo of orbital category 1 or 2". So why 1 and 2, but only 1 and 2?
Well, apparently only because if we limited it to orbital category 2, Jupiter would cease being a planet and become something else, while if we included 3 through N, the Moon would become a planet. So to preserve the status quo, we've got this definition that has no physical justification, or even excuse.
How about Quaoar and Sedna? I feel bad for them :I
I also think that we should boot Pluto straight out of there because it's orbit isn't even in the orbital plane of the solar system
There is no "orbital plane of the solar system". None of the 8 original planets share a common orbital plane. Their orbital planes just differ by a lot less than that of Pluto.
In any case, why should having a weird orbit disqualify Pluto? Why not, say, angle of rotation (Uranus is odd man out), or atmosphere (Mercury loses), or the presence of a solid surface?
Also, if orbit is the qualifier, Ceres would still make the list of planets.
Here's a special message to all who don't think Pluto should be a planet
Revenant:
Um, look here for a good description of how individual planets' orbital planes oscillate perpendicular to the solar system's invariable plane. The oscillations are so small compared to the scale of the solar system's size, that the invariable plane and average orbital plane are treated, for most intents and purposes, as equal. Unless you're actually measuring the oscillation, then I guess it's pretty important. I've mentioned, right, that I hate this stuff?
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