... doesn't always come around.

At least one of my "on this day" sources (later reliably corroborated by, what else?, a Google search) tells me that it was on this day, precisely one year ago (in 2005) that scientists discovered a (or should that be "the"?) tenth planet orbiting around the sun. There still (or perhaps "again of late") seems to be a debate over whether or not Pluto actually is a planet, or instead only a very large Kupier Belt Object (KBO). That being the case, has whoever authorized the formal reporting on the discovery of a tenth planet definitively determined that the ninth planet is actually what it's claimed to be?

Apparently not. Though the debate goes on, it seems that neither side in the astronomical community wants to force the other side's hand. Determining whether Pluto is or isn't a planet rests on determining precisely just what a planet actually is, and a definitive definition isn't that easy to come by. One very informative page gives both sides of the issue, but stops before making a call.

When I was a school kid, pouring over astronomy books that probably had as much to do with science fiction as they did with actual astronomy, Pluto was still very much a planet, but for years I've known that its planetary status has been questioned. A February, 1998 article in the Atlantic Monthly (When is a Planet Not a Planet? by David H. Freedman - sadly not publicly available on the web) points out that a precise classification isn't only a matter of science, but of public opinion as well:
Is Pluto truly a planet? A growing number of solar-system scientists assert that Pluto's minuteness and its membership in a swarm of like objects mean that it should be classified a "minor planet," as asteroids and comets are. Others are outraged by the idea, insisting that regardless of how its identity has changed, demoting Pluto would dishonor astronomical history and confuse the public. In the end, the debate boils down to this question: What compromises in precision should scientists make in the name of tradition, sentiment, and good public relations?
Freedman quotes astronomer David Levy who gives an important, but hardly astronomical, perspective to the debate. Demoting Pluto would be:
disrespectful to the public, Levy argues, and to children in particular. "Kids like Pluto," he says. The story of Ceres's [the largest of the asteroids in the asteroid belt] demotion isn't relevant, he claims, given that the public has never really thought of Ceres as a planet. Rather, he holds up the case of the brontosaurus. Early in the century paleontologists realized that the apatosaurus and the brontosaurus were actually the same creature; one of them had to go. Taxonomic convention dictates that the first- named species-in this case, the apatosaurus-subsume the second. And so it was that scientists dutifully declared the much-admired brontosaurus nonexistent. "Sure it's a rule, but every kid knows what a brontosaurus is," Levy says. "Why couldn't they have made an exception?" The brontosaurus has, of course, proved unsinkable in common usage. If astronomers ignore Pluto's place in popular culture, Levy warns, then popular culture could ignore them.
This would seem to be enough for a date tie-in. But in the spirit of this month's column, it's hard to stop here. Pluto's status, after all, offers us a good opportunity to observe how the Wikipedia deals with the issue. Although the question of Pluto's planetary status is a hotly debated issue, the debate rages (if that's the right word) almost solely in the scientific community. Does the Wikipedia article reflect that debate? Does it take sides? Or does it perhaps harken back to the 1950s when science seemed much surer of the way it defined things. From my own, non-astronomer's perspective, I'm very impressed with the article. It seems not only comprehensive but also fair to the opposing sides of the debate. No less interesting is the fact that it has gone through hundreds of edits since it first appeared as a short and concise article in March of 2002, blossoming into an impressive source that (to my mind at least) could be used as a reference. That being said, a glance at the discussion page about the article suggests that just below the surface of this calm and well considered encyclopedia entry lies a heated argument waiting to explode.

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