In addition to being the first dwarf planet discovered in our solar system, Ceres has the distinction of being the smallest, which makes its place as first-discovered even more unique. The next dwarf planet, Pluto, was not discovered until 1930. Nearly eighty years passed before any new planets were discovered, but between 2004 and 2005, three were added to the roster: Eris, Haumea, and Makemake. Why the long period between discoveries? Although scientists estimate there are dozens of dwarf planets in our solar system, their tiny size (Ceres, for example, is approximately 1.28 percent the size of the Moon) and enormous orbits (Eris takes nearly 560 years to orbit the Sun) make them especially difficult to pin down and observe.