One criterion for whether a body is a full planet rather than a dwarf planet is that it must “clear the neighborhood around its orbit,” meaning that it must be the gravitationally dominant object in its orbital zone. This is the criterion that Pluto fails to meet, because it has many a...
The Solar System has eight planets. In 2006, astronomers reclassifiedPlutoas adwarf planet, placing it in the same category as Eris, Sedna, Quaoar, Ceres, and potentially many other small bodies in the solar system. These are defined approximately as bodies that orbit the Sun but that are...