Twelve -- Count 'Em -- Twelve Planets

[billroper]

Well, at least we will have twelve planets and probably more soon if the current IAU proposal to define a planet (more or less) as a spherical body that orbits the sun is voted in. I think the definition is being a bit too inclusive. Something like Ceres or Pluto that is part of the orbiting rubble collection probably shouldn't be a planet.

Comments

[madfilkentist]

Calling Charon a planet just seems weird at first glance, though there is a logic to it.

But the analogy to stars doesn't seem to hold up well. Alpha Centauri is called a triple star system, not a double star system with a planetary star, even though Proxima Centauri is thought to orbit around the other two. If the nomenclature for star systems was applied to planets, I don't think there would be anything that qualified as a planet.

[blueeyedtigress.livejournal.com]

Hmm. If Pluto/Charon gets some sort of twin planet designation, then so, rightly, should Terra/Luna.

Calling Ceres a planet is like calling a feather a bird -- which SF author was it who referred to the asteroid belt as "the bones of Lucifer"? So if we just get around to saying, "yes, there was a planet there, it was retroactively named Lucifer, it was at the gravitational crack-point of this system, planet go boom", then we no longer have to worry about re-designation of roughly-round rubble ....

[billroper]

The center-of-mass for the Terra/Luna system is inside the Earth, as opposed to Pluto/Charon which is outside of Pluto. So Luna's a moon and Charon's a planet by these definitions.

Apparently, Lucifer never got its act together, so Ceres isn't a planetary explosion remnant so much as a large piece of the debris that couldn't coalesce to form a full-sized planet in that space.

[blueeyedtigress.livejournal.com]

Ah, the definitions must have modified on me. Thanks for the clarification!

[min0taur.livejournal.com]

Well, if you consider that both Jupiter and Pluto are (or were, in the century I come from) both considered planets -- and that the actual definition of what a planet *is* has been kind of informal for quite a few centuries, maybe what we got here is a conceptual growing-pain that goes along with the increased rigor encouraged by improved observational technology. I don't mind if we end up with "more" planets in our system; kinda makes me feel like I changed cosmic neighborhoods after all (in the solar system I come from, there was only one ringed planet), even without m'damn spaceship. All ya gotta do is move ahead in time, even if ya gotta walk. Of course, what'll *really* be interesting is when we find objects that meet all the criteria for "planet" and throw in some other attributes (say, of "star" or "comet" or "creature") just for fun.