The (ex)Planet Pluto - Facts and Information

Textbooks since 1930 have listed Pluto as a planet.  It was the farthest known planet from our Sun.  In 1996, the International Astronomical Union demoted Pluto to dwarf planet status.  This has created an uproar in the astronomy community with many people having a strong opinion on this issue.  Pluto is one of probably thousands of objects larger than 100km in the Kuiper Belt, a region of mostly icy objects that orbit beyond Neptune.

Pluto has a  highly elliptical orbit that sometimes takes it within the orbit of Neptune, most recently in 1979.  Due to Pluto's extreme distance from the Sun (almost 6 billion km), it takes 248 years to make one full orbit around the Sun.  Pluto's diameter is a bit over one-half the diameter of our Moon.  It is believed to have a small rocky core surrounded by frozen ice.  When Pluto is on the portion of its orbit that takes it farther from the Sun, Pluto remains completely frozen.  When Pluto's orbit takes it a bit closer to the Sun, some methane, nitrogen, and carbon dioxide are released.

Pluto has three moons; Charon, Hydra and Nix.  Charon is about one-half the size of Pluto.  Hydra and Nix are two much smaller moons that may have formed from another object's collision with Pluto.  Pluto and Charon actually form a double planet system.  No spacecraft has visited Pluto as of yet.  However, NASA's New Horizons is on it's way.  New Horizons was launched in January 2006 and will not arrive to Pluto until 2015.  It will study and photograph Pluto, Charon, and other Kuiper Belt objects which have yet to be selected.  For the first time, we will have close up pictures of these objects.