Pluto as ‘Planet’

I have never been exactly indignant about the demotion of Pluto to ‘dwarf planet’ status but I do think it’s curious and in at least one respect too arbitrary for my taste. I’ll buy the idea that a planet needs to be round because of its own gravity, and I’ll sign off on the notion that to be a planet, an object has to be in orbit around the Sun (even though we do have apparent wandering planets in the interstellar deep, far from any star). But the International Astronomical Union also decided in its 2006 deliberations that a planet has to ‘clear’ its neighborhood of debris, thus sweeping out its orbit over time. That one, of course, is controversial.

Assuming the Earth is a planet, why are we worried about things like Near Earth Asteroids (NEAs)? Our planet clearly hasn’t swept out its neighborhood, not when we can number problematic asteroids in the thousands. Jupiter is estimated to have about 100,000 trojan asteroids in its orbital path as well, and Alan Stern, principal investigator for New Horizons, has pointed out on more than one occasion that if Neptune (obviously a planet) had cleared its orbit, Pluto itself wouldn’t be there, and the whole discussion might never have come up.

For that matter, we would not be having this discussion now if not for continuing discoveries in the Kuiper Belt that more or less force the issue. Eris was found in 2005, a world more massive than Pluto and first thought to be larger as well, leading to the temporary designation of it as the ‘tenth planet,’ and raising the question of what to do about a Kuiper Belt that might be stuffed with such objects. Here the matter seems to be one of simple redundancy. Nine, or eight, planets, is acceptable. Several thousand is not — it seems to devalue the notion altogether.

I can see why working this out is still controversial. Meanwhile, from a purely aesthetic point of view, I have a hard time looking at the image below and seeing it as anything other than a planet. Or, as I have said before, the larger component of a binary planetary system.