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pluton



  1. (GEOLOGY) Any body of igneous rock that solidified below the Earth's surface.

       • GEOLOGY AND PLANETARY SCIENCE

  2. (ASTRONOMY) A proposed category of planetary object, of which Pluto would have been the prototype, consisting of planets that takes at least 200 years to complete one orbit of the Sun. Astronomers instead adopted the term "dwarf planet" to distinguish smaller planetary objects from the eight "classical planets," Mercury through Neptune.

       • PLANETS AND MOONS