Pick a Definition, Already!

As an astronomer, I don't know why astronomers are so hung up on this. Or, rather, I do. It's not because astronomers are hung up on it, but it's becuase the general public wants a clear, cut-and-dried definition of what a planet is. Unfortunatley, it's just not so clear. All those objects are what they are. I think it's clear that the classification system that gave us nine planets is wanting.... Unfortunately, there is a lot of public pressure, not pressure from astronomers, to keep Pluto as a planet.

The reason that astronomres are hung up on this is because people in the general public pay attention to it. Can you imagine what a mess there would be if the general public understood the whole issue of observers and measurement in quantum mechanics?

There are other messes in astronomy classification as well, but generally we just run with them and don't worry about them, becuase the public and media aren't aware. Type I and Type II supernovae started out as a pure observational distinction, based on a seemingly good criterion: the presence or absence of Hydrogen lines in the spectrum. At the time, the physics of the supernovae weren't well understood. Now, we know that some Type I supernovae are more like Type II supernovae than they are like other Type I supernovae, so we have Ia, Ib, Ic, etc. I tend to call them "core-collapse" and "thermonuclear" supernovae, because that expresses the physics. If the public were aware of and cared about this classification, there'd be a lot fo bruhaha as well.

Phil Plait already has made the argument that we're just getting hung up over semantics. There is some real science behind all of this -- what sorts of bodies formed in the Solar System, and how are they different from the other sorts of bodies that formed? -- but it's turned into politics and lobbying.

-Rob

Sorry Rob, but you astronomers obviously have some criteria for what is and isn't a planet. If there's a general sort of rule, with some exceptions, just tell people and go back to star gazing.

Now, I'm not cool with calling the oversized asteroid a planet. Yet. I mean, all of the planets in our little corner of the galaxy started life as a ring of debris orbiting our little star, and coalesced over time, so I expect in a little time, we can expect the same from the ring of debris separating the little planets from the monsters to do the same, yes?

Of course, some day Jupiter and Saturn will have less rings and more moons for the same reason if we can believe you hippies. We know you just star at the sky for hours because you got baked.

I refuse to read any more about this nonsense until astronomers pull their heads out of their asses and start talking about Rupert.

it's becuase the general public wants a clear, cut-and-dried definition of what a planet is.

Isn't this an issue with the long-held belief that definitions are cut-n-dried in ALL the sciences?

Consider "Species" - once, under the age of reason and Linneus, a clear cut concept - we all just *knew* what a species was. Today? Nobody knows a damn thing. Every limit we try to put to distinguish between species has examples in nature that violate that limit, be it isolation, shape, inter-species reproduction, sterility (or not) of intra-species reproduction (in plants even more than animals), etc, all conspiring together to make it impossible for the word "species" to have any universal meaning in science.

So too, planets. New discoveries cause new associations and patterns to be seen, and in those patterns, Pluto is less of a "planet" than it was all those years ago when compared with the others.

So either the definition of Planet changes (the current proposal), or we continue to debate the classification of Pluto (and friends).

In either case, tradition is lost because no matter what, there won't be 9 planets anymore. And this again goes to the problem of the layperson in science. the layperson expects things that science discovers to be constant, that once science has said X, then X is always true. science has no such hangups (though individual scientists can be blindsided by hangups they didn't recognize, hence peer-review).

PS - Dennis: I too keep insisting we call it Rupert. It's been named, its been described by effectively a futurist exactly as it ended up being discovered, so go with the name the man who predicted it (granted, with more fancy than fact) gave it.

"Xena" indeed... At least when the asteroids got named for rock and synth musicians, there was some talent involved.

Honestly, this is why physicists sneer at astronomers. Not only do they use dumb units, and have the axes backwards on most of their graphs, they spend too much time fussing about with names. They're almost as bad as those damn biologists.

That's because the things we study are complicated, unlike the simple, boring things you physicists worry about ;-)

As for backward axes -- well, you got me there. (The only excuse is the sheer antiquity of astronomy: we're still using "units" invented over two thousand years ago.)

My favorite goofy plots are from the X-ray astrophysicists, who like to plot energy versus energy. (As in "energy received from source" vs. "energy of photons.")

Sorry Rob, but you astronomers obviously have some criteria for what is and isn't a planet.

Oh, there are lots. But there sure isn't a single, unambiguous set of criteria that every astronomer would agree on. What's more, many astronomers are like me-- we don't really have much of an invested interest in it, but we do recognize that if Pluto is a planet, then lots of other things (including, probably, Ceres) are also planets under any rational science-based definition. If those other things aren't, then Pluto isn't.

But, honestly, it doesn't really matter to me what the official nomenclature is, so long as we continue to learn more about what the things are and how they formed, etc.

The term "planet" has meant different things throughout history. There have been windows of time when it seemed that there was a clear, unambiguous definition that had some things in and some things out. Until the last couple of deacdes of the 20th century, we were in one of those windows of time. Right now, it's clear that there is not a simple, obvious definition that will make everybody happy... and insisting that we have one, or trying to force one, just makes a mess.

-Rob

Pet peeve about "Xena". That's just a nickname the discoverers have been using in the press because 2003UB313 is boring to non-astronomers. They actual permanent name they've suggested has not been revealed to the public, and won't be until it is voted on. For all we know, it may actually be Rupert.

The answer is simple.

Write a definition to fit the eight objects almost everyone agrees are planets. Then add an exemption for any objects traditionally regarded as plenets prior to the enactment of the new regulation...

:)