When the International Astronomical Union (IAU) adopted a new definition of a "planet" in August 2006, Pluto became a dwarf planet, drawing a divisive line in science and public opinions. The controversy of whether Pluto is a planet continues years later, and passion about the decision remains, pitting scientist against scientist and invoking sentiments and nostalgia from the rest of the world. With the IAU definition, the future of space objects...