Which Of Our Solar System’s Dwarf Planets Was Discovered First?
Although Pluto might be the most famous of the dwarf planets in our solar system–especially after 2006 controversy demoting it from the planet to dwarf planet classification–it wasn’t the first to be discovered.
The earliest observation of a dwarf planet dates to 1801 when it was discovered by on New Year’s Day by Italian mathematician and astronomer Giuseppe Piazzi. Piazzi observed the unknown object for several days before losing it in the glare of the Sun. Based on those observations he was unable to calculate if it was a planet or comet and opted for a more conservative estimate that it was a comet passing through our solar system. Later mathematicians, including Carl Friedrich Gauss with his new methods of orbit calculation, determined that it was in fact a dwarf planet.
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, wasn’t discovered until 1930. Nearly eighty years passed before any more dwarf planets were discovered but between 2003 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 roughly 1/3rd the size of the Moon) and enormous orbits (Eris takes over 560 years to orbit the sun) make them particularly difficult to pin down and observe.