Planets again

[mmcirvin]

...And now the AP says the IAU has gone in the less expansive direction, distinguishing between dwarf planets and real planets and demoting Pluto. I can't tell exactly from the article but it sounds as if there's a qualifier that excludes objects obviously part of a population of similar bodies in similar orbits.

(The article claims that Pluto is disqualified because its orbit "overlaps" Neptune's, but that can't be right without further detail, or it would disqualify Neptune too! I would think that Pluto is disqualified because it's one of a whole population of similar bodies in similar orbits, some of which are of comparable or even greater size.)

Comments

[paracelsvs.livejournal.com]

Why didn't the earlier suggestions just dump the overly complicated and confusing nonsense about barycenters, and just say "NO SATELLITES ALLOWED" like the new one? That would have gotten rid of the Pluton-Charon double planet, which I am sure was way too silly for too many people to allow it to stand.

[mmcirvin.livejournal.com]

Personally, I would have liked that best: let in all the little guys that are round but aren't moons, and just be sensible about what is a moon. Let Pluto and Ceres and 2003 UB313 and Sedna and dozens or hundreds of other Kuiper Belt objects be planets, but don't mess around with the relatively obvious classification of satellites.

(I suppose if you squint sideways at the "dwarf planet" designation, the adopted definition looks something like this. But it sounds as if "dwarf planets" are no more supposed to be proper planets than "minor planets" before them.)

Ultimately, though, I think what most of the IAU wanted was a physically motivated definition that gave something close to the accepted nine-planet lineup. And the only thing you can really sensibly do given those two criteria is demote Pluto. In and of itself, that's logical. What dissatisfies me is that the wording of the definition as adopted is so vague; it could have been better.