The Nature of Planets, Dwarf Planets, and Space Objects

The Nature of Planets, Dwarf Planets, and Space Objects — page 9
THE NATURE OF PLANETS DARF PLANETS AND SPACE OnTECTS enough for its gravity to have pulled it into a nearly spherical shape Third it must have cleared the neighborhood around its orbit meaning that it must be massive enough for its gravity to have removed most rocky and icy debris from the vicinity of its orbit Pluto is not a planet under this definition It orbits the Sun and is nearly round but it has not cleared away many small Kuiper belt objects from the area around its orbit The IAU created a new category called dwarf planet for those nearly spherical celestial bodies that orbit the Sun but that have not cleared the area around their orbits and that are not moons The first bodies to be des ignated dwarf planets were Pluto Eris and Ceres which is also the largest asteroid The IAU definitions were themselves con troversial Some scientists welcomed them as appropriate recognition that Pluto is one of the larger objects in the Kuiper belt Other scientists criticized the definitions lack of precision and scientific rigor and called for their revision CLASSIFICATION OF THE PLANETS The eight planets of the solar system can be divided into two groups inner planets and 14