For the past few decades, the Solar System, according to every astronomer you could find, had nine planets. Last summer, however, the convention of the International Astronomical Union decided there were only eight planets, demoting Pluto to dwarf planet status. Recently, the Hubble Space Telescope imaged Ceres, heretofore the largest asteroid, and found it to be spherical, like an honest-to-gosh world. Ceres, about half the diameter of Pluto, is also now a dwarf planet, according to the new IAY definition.
The demotion of Pluto seemed to hit a nerve in the interested public, but another part of the new regime is more curious. The IAU limited its definition of "planet" to this solar system. IAY members have currently found over 200 such bodies orbiting other stars, and the pace of discovery will almost certainly quicken over the next few decades. Astronomers were the first scientists to show that the same physical laws that operate on Earth also operate throughout the universe, but they have decided bodies in our Solar System are to be defined one way, while bodies in some other system might be defined some other way.
Maybe this bunch wanted to give those who come after them something to do.