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

[mmcirvin.livejournal.com]

Probably they were worried that something about their definition might not apply to other star systems, and decided to kick that vote down the road a way once there's more data. As James noticed, the decision seems to deal mostly with the ambiguities at the small end of the planet definition, since the planet/star distinction is quite clear in our own solar system; but it is not at all clear when one considers the 200+ extrasolar planets known. A definition that applies to extrasolar planets would have to deal with the separate question of what constitutes a star or brown dwarf, and whether any of these are planets. And that's probably a whole other round of infighting.