1930: Pluto was discovered by Clyde Tombaugh and designated the ninth planet in the solar system (the name Pluto was suggested by 11-year-old Venetia Burney of Oxford, England) January 19, 2006: The New Horizons spacecraft was launched on a voyage to Pluto August 24, 2006: The International Astronomical Union voted to accept a new definition of "planet," which excluded Pluto, making Pluto a dwarf planet (along with Ceres, Eris, Makemake, and Haumea) May 14, 2015: This episode aired, in which Riley calls Pluto "The smallest planet with the biggest heart." July 14, 2015: New Horizons made its closest approach to Pluto and sent back pictures showing a large light-colored feature on the surface of Pluto in the shape of a heart (with a tail)So Pluto isn't officially a planet, but it does have a big heart.