Why Is Pluto No Longer Called a Planet?
In 2003, U.S. astronomer Mike Brown discovered a new object beyond Pluto. Brown thought he had discovered a new planet because the object, which he named Eris (EER-is), is larger than Pluto. The discovery of Eris caused other astronomers to talk about what makes a planet a “planet.” The International Astronomical Union is the group of astronomers responsible for naming objects in space. The IAU decided that Pluto and objects like it were not really planets at all because of their size and location in the solar system. The IAU decided that Pluto and objects like it should now be called dwarf planets. Pluto also is called a plutoid. A plutoid is a dwarf planet that is farther out in space than the planet Neptune. The three known plutoids are Pluto, Eris and Makemake (MAH-kee-MAH-kee).
