Learn the three criteria for classifying planets and discover why Pluto is now considered part of the Kuiper belt. When Pluto was discovered in 1930 it was classified as the ninth planet in the solar system. For decades Pluto was believed to be much larger than it actually is, based on incorrect interpretations of observations. Advances in technology brought about new knowledge of Pluto and it is now recognized to be a member of the Kuiper reclassified as a dwarf planet. In 2006, the New Horizons mission was launched; it will be the first spacecraft to visit Pluto and the Kuiper belt.
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