Eris is the largest dwarf planet in the Solar System, and the ninth largest body orbiting our Sun. Sometimes referred to as the “tenth planet,” its discovery is responsible for upsetting the traditional count of nine planets in our Solar System, as well as leading the way to the creation of a new astronomical category.
Dwarf Planets of Our Solar System (Infographic) by Karl Tate In 2006 the organization responsible for classifying celestial bodies, the International Astronomical Union, decided that a new class of objects was needed. The solar system's erratic ninth planet, Pluto, was assigned to the new “dwarf planet” category along with four other bodies, all tinier than Earth’s moon. Some astronomers expect there may be as many as 50 dwarf planets in the solar system.
Two spacecraft, Dawn and New Horizons, will reach their final objectives in 2015 – Dwarf Planets Ceres and Pluto, respectively. (Credit: NASA, Illustration – T.Reyes) The Solar System is becoming a more crowded place. This picture shows the sizes of dwarf planets Pluto, Ceres, Eris, and Makemake as compared to Earth and Earth's Moon, here called "Luna." None of the distances between objects are to scale. (Credit: NASA)