what is a planet?

After a few thousand years, scientists are finally working on an actual definition.

If the proposed (International Astronomical Union) Resolution is passed, the 12 planets in our Solar System will be Mercury, Venus, Earth, Mars, Ceres, Jupiter, Saturn, Uranus, Neptune, Pluto, Charon and 2003 UB313 (possibly to be named Xena).

There will most likely be more planets announced by the IAU in the future. Currently a dozen "candidate planets" are listed on IAU's "watchlist" which keeps changing as new objects are found and the physics of the existing candidates becomes better known.

Part of the problem is that Pluto is goofy...