Question: why has pluto been reclassified as a dwarf planet?
Answer: After 1992, its status as a planet was questioned following the discovery of several objects of similar size in the Kuiper belt. In 2005, Eris, a dwarf planet in the scattered disc which is 27% more massive than Pluto, was discovered. ... That definition excluded Pluto and reclassified it as a dwarf planet.