Pluto, along with the other trans-neptunian objects of a similar size discovered in the late half of the 20th Century, could not be considered the same as the terrestrial planets. The final nail in this coffin was the discovery of Eris in 2005. They are smaller and have not necessarily cleared the neighborhood around their orbit. Instead, they fit into a classification of their own, as 'dwarf planets.' This term was introduced by scientist Alan Stern as part of the new classification introduced in 2006.