|The Pioneer plaque|
Our initial inclusion of Pluto as a planet is an example of our failure to group objects by their characteristics. Neil deGrasse Tyson, an American astrophysicist, advocates looking at commonalities between astronomical objects and moving away from simply counting the planets. He sees the terrestrial planets as one group, the gas giants as a second, and Pluto and like objects as a third. This makes a great deal of sense to me. It's too bad the reclassification of Pluto by the International Astronomical Union didn't happen before the Pioneer plaques were dispatched to the stars. What might an extraterrestrial think after looking at that ninth circle?