Retreating from crazy, IAU proposal is now just bad
I should point out that my diatribe below about the crazy IAU proposal being debated this week is already obsolete, since an amendment to the original definition was adopted earlier today that would trim the number of planets from the proposed 53 (masquerading as 12) down to just 8. This decimation of the population was accomplished by adding one simple phrase, that the object must dominate its region of space. That immediately knocks out Ceres (part of the asteroid belt), and Pluto, Charon and 2004 UB313 (parts of the Kuiper Belt). So instead of gaining 44 planets, the solar system loses one, namely Pluto, and everybody who cares at all about this is just going to be very ticked off (except Neil Tyson of New York's Hayden Planetarium, who had already made the decision to go to just 8 planets).
It's an improvement over having 53 planets, which obviously nobody was going to take seriously, and eliminates the craziness of including Charon, and the weirdness of including Ceres. But really, what's the point?
Defining the "region" that must be dominated by a planet is intrinsically arbitrary. So why bother? If we're going to have an arbitrary definition, on a matter that affects culture far more than it does science, why not use the arbitrary decision that fits harmoniously with what culture has overwhelmingly agreed on, and is simpler and easier to rememeber to boot? Accept anything bigger than Pluto, or (virtually the same thing) bigger than the nice round 1,000 km radius, and everybody's happy. Kill off Pluto as a planet, and no scientific purpose is served, but lots and lots of people will be very angry. That's the choice that the astronomers in Prague now seem to be heading toward, like lemmings streaming toward a cliff.
Clark Chapman, an asteroid and comet specialist at the Southwest Research Institute in Boulder and someone who has spent a lot of time researching and thinking about the way astronomy is communicated to the public, agrees with the size-cutoff idea, as does Michael Brown, the discoverer of the "tenth planet." But almost nobody else has spoken up publicly for this simple, commonsense solution. Here's what Clark said about it in a recent email he sent me:
"Because the public is interested and involved, and because historical precedent is important, the solution I preferred (and sent last week to some of those involved in the Prague discussions) would have been to accept the nine planets we have had for most of a century, and add anything as big or bigger than Pluto to the list of planets."
Too bad he's not in Prague. I'm not sure if Brown is or not. We'll see what happens.