August 19 Update

As described here by Rob Roy Britt, the IAU has come up with an alternative proposal for defining planet-hood. This one looks more sensible and is a lot simpler: I can imagine explaining this one at my daughter's school and having the kids understand it immediately. It is also closer to the way most people working on the outer Solar system think about the Kuiper belt objects, including Pluto.

Other advantages:

1) It avoids mixing apples and oranges: tiny Ceres and 2003 UB313 would not be confusingly lumped in the same category with gas giant Jupiter.

2) It avoids strange consequences (e.g. that our Moon will become a planet, or that a binary in elliptical orbit could be a planet only for part of each orbit).

3) It avoids stealing a term "Pluton" from the geologists (a pluton is a large intrusive mass of igneous rock). Evidently there were no geologists on the IAU committee.

4) It doesn't make the IAU look as silly as their first proposal did.

All in all, I'd probably vote for the alternative proposal, if I were able to do so.

David Jewitt.

Comet Jewitt Kuiper Irregular Satellites