It seems the hoo-hah over Pluto and the newly-voted-upon definitions of “planet” and “dwarf planet” and “plutonians” (which reminds me of a race of science-fictional beings with green antennae wiggling around on their heads) is hardly over. Oh, at first glance, as I mentioned in previous entries, it seemed like a good way to finally get some definitions that make sense and help us figure out how to categorize things in the solar system.
Unfortunately, the new definitions don’t always help. If you apply some of the “rules” described in my previous entry, you could end up with some pretty ludicrous outcomes. Take, for example, the idea that a planet has to have “swept its orbit clean” dynamically. What, exactly, does that mean? Well, when a solar system forms, the larger pieces get glommed together (the technical term is “agglomerate”) from smaller pieces. The bigger agglomerations attract or sweep up the smaller pieces. Eventually a planet (or planet-like entity) forms out of these sweepings, leaving surrounding space reasonably clear of the planetary birth leftovers. While this is an important step in the creation of a planet, I’m not so sure it should be given as much weight as it has been in the IAU definition that was approved.
But, when you apply this “a planet sweeps up its surroundings” rule, you could get in trouble. Let’s say you discover a star that has a bunch of planets around it, and there’s one the size of Jupiter in the collection. Great, sounds like a planet, right? But, what if it’s surrounded by a huge ring of debris, larger than Saturn’s, and clearly the “stuff” hasn’t been swept up by the planet—yet. By strictly applying the definition, if it hasn’t cleaned up its environment, that bad boy ain’t a planet.
Of course, there’s the whole issue of whether that Jupiter-sized thing is in hydrostatic equilibrium and “roundish.” So, right there you have conflicting reasons to call it a planet—or not.
That’s just one example. People are discussing this whole thing. Planetary scientists like David Jewitt of the Institute for Astronomy in Hawai’i, are commenting on their web pages and publicly about the ramifications of the defnitions. More are coming up with other examples that provide tests of the system, and in some cases, point out how silly parts of the system are. Right there, it looks like cooler heads need to prevail over the small percentage of astronomers who took matters into their own hands at IAU and summarily rewrote definitions on the fly. Will cooler heads prevail? Good question, but in the meantime, we have been privileged to see “astronomers behaving badly” at the IAU (in the words of one of the attendees who was there for the discussion sessions and the vote). I think there’s some great street theater occurring in astronomy and planetary science circles, and that means this thing ain’t over yet.
Already there is a petition going around among some really well-known and respected planetary scientists denouncing the whole contretemps at IAU and refusing to use the new definitions. It may gather lots of steam, and that steam may come to a rather explosive head at the next IAU general congress in 2009.
Still, dissent means we should get a much better definition. And, as I keep saying, this can only serve to strengthen the science we do, and keep reminding us that the scientific process is not one of arbitrary standards and wishful thinking, no matter how badly some astronomers may behave at any given time.
Speaking of astronomers behaving badly, I am reading a really good book right now called Stargazer: The Life and Times of the Telescope. It’s written by Fred Watson, who is the astronomer-in-charge at Anglo-Australian Telescope in Siding Spring, Australia. Fred gave a talk at the International Planetarium Society meeting in Melbourne last month titled “Astronomers Behaving Badly,” in which he detailed some of the astronomical hijinks of past astronomers. He also explains these in great and amusing detail in his book. You also get a nice little introduction to the development of the telescope, which is sort of the whole point of the book. I wonder what Fred will write (providing he’s still around) in some future decade about the astronomer hijinks over Pluto?