III.

Origin of Pluto

With a density about twice that of water, Pluto is apparently made of a much greater proportion of rockier material than are the giant planets of the outer solar system. This may be the result of the kind of chemical reactions that took place during Pluto’s formation under cold temperatures and low pressure. Many astronomers think Pluto was growing rapidly to be a larger planet when Neptune’s gravitational influence disturbed the region where Pluto orbits, a region known as the Kuiper Belt, stopping the process of planetary growth there. The Kuiper Belt is a ring of material orbiting the Sun beyond the planet Neptune that contains millions of rocky, icy objects like Pluto and Charon. Charon could be an accumulation of the lighter materials resulting from a collision between Pluto and another large Kuiper Belt Object (KBO) in the ancient past. Scientists are interested in Pluto and other KBOs because they likely represent the type of primitive bodies and material from which the solar system formed.