Well, not new, really, but newly defined perhaps. The leaked decision is causing a bit of a stir in the astronomical community, which might lead to further changes, but for now it looks like a “planet” is something massive enough for its own gravity to collapse it into a sphere, and that also orbits a star and not some other planet. What’s more, Charon and Pluto appear to be slated to become a double-planet rather than a planet and its satellite. Perhaps the center of gravity of the Pluto-Charon system is such that neither really dominates, and hence they both orbit the sun on more-or-less equal footing. Ceres, perhaps formerly known as the largest asteroid, is getting the nod, and 2003 UB313, a KBO bigger than Pluto, may also make the cut. I’m guessing Quaoar and other large KBOs are also strong candidates. There could be dozens of “planets” out there orbiting our sun!
Now I know this isn’t a done deal yet, but it does appear to be a distinct possibility. So what do y’all think? Are you ready for Ceres to be the fifth planet, and Pluto, Charon, and “Xena” to be the 10th, 11th, and 12th, respectively? Ready for even more than that, as would be likely if this becomes official? Are you going to get a headache trying to remember all the new planets? Do you even think this is a good idea, or does it sound wacky? This should be a fun discussion!
This is an incredibly pussy decision. Not the woman kind: the manly man cowering behind a desk kind. This whole extra layer of confusion is being added in for the purposes of NOT demoting Pluto from planetary status… and all based on what, exactly?
If astronomy were some sort of administration voted into office by kindergardeners, I could see the point. But they are bowing to the pressure of, it seems, a bunch of kooks who spend their time obsessing about the fate of Pluto! WHO CARES. Just demote the damn thing out of planet status and be done with it. Let the “Save Pluto” campaigns rage at nothing for no purpose.
Geez: you’d think federal funding depending on the classification or something.
I must admit, I thought Pluto was bound to get the axe, simply because any rational scheme that includes it would also have to include at least “Xena”, and probably Quaoar, Ceres, and what is likely to be a swarm of other large bodies in the Kuiper belt. When you consider that the mass of Jupiter is around two times greater than all the other mass of the Solar System combined (not including the Sun, of course), one could reasonably argue that only the gas giants are “planets” and the rest is essentially rocky debris.
I really thought there would be some kind of hexapartite scheme they’d settle on with clearly delineated catagories (mostly of in order of AUs from Sol):
Rocky Planets: Mercury, Venus, Earth, and Mars.
Gas Giant Planets: Jupiter, Saturn, Uranus, Neptune
Asteroids: All the rocky and/or metallic stuff out there equal in size or smaller than Ceres and not a moon.
Kuiper Belt Objects: Pluto, Charon, “Xena”, Quaoar, etc.
Comets: Icy things in highly elliptical orbits that can grow those pretty tails, and which might otherwise be KBOs, or, more likely…
Oort Cloud Objects: All the primordial stuff way the heck out in a roughly spherical cloud around the Sun that’s also a source of comets. There might be some big chunks of whatever out there, barely within the grasp of the Sun’s gravity, almost a light-year away, or maybe even a little more.
Instead they’ve basically got the above scheme, but one of 3 and a boat-load of 4 get lumped in with 1 & 2 because they’re spherical.
I’m absolutely ok with that as long as they give that one a real name - you know, one that isn’t based on a trashy TV series. If that name remains, I’ll petition for renaming Jupiter to “That ruby-collecting skull from the Conan series.”
I didn’t see any particular problem with continuing on with no technical definition for planet. There is no cutoff in nature for “planetness” that I can see, at least at the small end. There are a few dozen distinct, individual objects in our solar system, no matter what you call them. Titan and Io are no less interesting than Mercury or Uranus simply because they orbit planets rather than are planets.
I agree that this proposed definition feels like a way of coming up with a set of rules that doesn’t change too much but justifies calling Pluto a planet while simultaneously attempting to mollify the anti-Pluto crowd with the whole Pluton thing (which is already not good given that “pluton” already has a geological meaning).
A lot of the arguments I’ve heard over the last few years in favor of defining what a planet is have been based on the idea that the public would be confused without a definition for planet, particularly given the frequent discoveries of large KBOs recently. I don’t know that I buy that at all.
I will admit to being a bit tickled, though, since a paper I originally submitted on the asteroid 1 Ceres was revised and sent back in today with “planet Ceres” in my new title.
(On preview, what Loopydude said. And I’m thinking of the name Khaos for UB313…)
I’m agin’ it. Look, first, if we redefine what a planet is, we’ll have to come up with new mnemonics. I mean, we all know “My Very Educated Mother Just Served Us Nine Pies”, or some variant. Why change that?
Secondly, Charon, “Xena”, Quoaor, etc., are pretty pitiful sizewise. I mean, Mercury’s big next to them. I know, you can say the same thing about Pluto, but it’s already considered a planet and is named after a major Roman god, so there’s no harm in letting it stay. Beside, there’s that mnemonics issue if we demote Pluto. But the line has to be drawn there.
I think the definition makes a lot of sense. There are two aspects to it:
(1) Size. Too big, and you’re a star. Too little, and you’re just a lump of rock. However, if Ceres is in, then I think that Pallas and Vespa are in too.
(2) Orbit. You have to be orbiting round a star, and not round a planet. So the Moon and Ganymede are out, because they are satellites – and Charon is in, because it doesn’t orbit round Pluto, but around a point in between them.
Any definition has to be arbitrary to a certain extent, but this is less than any alternative that I’ve heard. And it gives us one really interesting object: the only known double planet, the Pluto-Charon system.
“Xena” will definitely get renamed. In keeping with tradition, I’d like to see the name Persephone used. Just another mythological underworld name; baby, it’s cold out there.
Cripes, I ought to read my own cites better. This is stated clearly in the article, clarifying that a “moon” is part of a star-orbiting system where the center of gravity is inside of the largest member of that system.
One could argue that the Moon is a planet since both it and the Earth orbit around a common point. Of course this point is in the Earth’s crust, but not at the core.
Still inside the Earth, though, so the definition of moon for the Moon holds. No gravitationally-bound system has members that orbit precisely around the center of the largest member, though some, like the Jovian system, are going to be pretty close.
(Wouldn’t that be embarassing though! The Moon redesignated a planet! “No, son, the Moon’s not a moon. I know it’s called the Moon, but it’s a planet! Well, I don’t care if you think it’s stupid, that’s just the way it is!”)
Except much of modern science IS perforce reviewed “by committee”. The fundamental objection would be the committee shoehorned the definition in order to “Save Pluto” in an act of science by public opinion, or science by cultural reference.
But part of the problem is that “planet” did not have an objective definition – it was always pretty much based on common usage and appearance rather than a concrete technical criterion. Originally a movable star, later refined to a naked-eye visible celestial object orbiting the center of your solar system, under which definition in Ptolemaic astronomy it was Sun, Moon, Mercury, Venus, Mars, Jupiter, Saturn; then it became a large visible celestial object in primary orbit around the Sun, in the Copernican/Galilean system Mercury, Venus, Earth, Mars, Jupiter, Saturn; THEN it became* a celestial object in primary orbit around the sun, that by size and orbital characteristics seems comparable to the six objects previously referred to as such,* which was what they ran with for 200+ years and by the comparability criterion excluded Ceres, but left Pluto just this side of the borderline for long enough to acquire cultural standing (a lot of what was initially observed as characteristics of a reasonably-sized “planet” out there may have been really combined characteristics of the Pluto-Charon double, mistaken for a single larger object, plus errors of observation at such range.)
So at least now there would be a set definition… if a bit broader than some would like.
