Interesting article, Peter.

It strikes me that the members of the International Astronomical Union need something constructive to occupy their time with so they don't just bumble around bumping into things and clumsily knocking them over. As far as the possibility of trans-Neptunian planets is concerned, I tend to think that there may be bodies even further out than Pluto that could qualify as planets, but simply haven't been discovered yet. As the article points out, there are a lot of things wrong with their so-called "definition" of "planet."

I had always thought that if a body was of sufficient size and mass that gravity shaped it into a globe, and if it followed its own orbit around the sun rather than orbiting another more massive body (such as the moon orbiting the earth), it's a planet.

There are some astronomers that actually feel that the Earth-Moon system should be classified as a double planet. I would think that if the barycenter is beneath the surface of the more massive body, then it's a planet and satellite, but if it lies outside the surface, it would be a double planet. The barycenter of the the Earth-Moon system actually lies within the earth, but close to the surface, so the double planet idea might be questionable. But with the Pluto-Charon system, the barycenter lies between the two, above the surface of Pluto, so it would qualify as a double planet.

Maybe instead of losing a planet, we've gained one!

This Wikipedia article (Center of mass) contains animations (scroll down) of various systems showing barycenter relationships

Interestingly enough, the barycenter between the Sun and Jupiter is above the surface of the Sun. Jupiter actually emits more energy than it absorbs, and there is some speculation that had Jupiter been just a bit more massive, nuclear fires would have ignited in its core (there may actually be!) and we'd be in a binary star system.

Alpha Centauri is such a system, with Alpha Centauri A a main-sequence star like the sun but just a smidge larger, Alpha Centauri B about 30% the size of Alpha A and about as far out as Uranus is from our sun. According to some astronomers, there should be a "temperate zone" about 100,000 miles out from Alpha A where a very earth-like planet (inhabitable very comfortably by human beans) could exist. During the times when the planet is between Alpha A and Alpha B, it would be bright enough to read a newspaper at night. Seasons might be a bit interesting, but nothing humans would find particularly uncomfortable. Proxima Centauri is a red dwarf and far enough out from the barycenter that, other than seeing it as a bright red star, it wouldn't have much effect on the theoretical planet.

Don Firth