On August 24, 2006, the general assembly of the International Astronomical Union approved the current system of classifying planets in our solar system. This system added a specific scientific requirement for planethood: It must have cleared all other significantly sized bodies out of its orbital path or neighborhood, probably through collisions or gravitational interactions. This system also creates a new designation called a “dwarf planet,” which describes an object that fulfills all the criteria of a planet except this one. This system, like every other classification that has come before it, has strengths and weaknesses; no matter what, though, it gives all people a starting point to learn about—and, we hope, understand—what planets are all about.

This current classification system means that, officially, there are eight planets in the solar system—Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, and Neptune—and a number of dwarf planets, including Pluto, Ceres, Haumea, Makemake, and Eris.