Once known as the smallest, coldest, and most distant planet from the Sun, Pluto has a dual identity, not to mention being enshrouded in controversy since its discovery in 1930. On August 24, 2006, the International Astronomical Union (IAU) formally downgraded Pluto from an official planet to a dwarf planet. According to the new rules a planet meets three criteria: 1. It must orbit the Sun 2. It must be big enough for gravity to squash it into a round ball 3. It must have cleared other things out of the way in its orbital neighborhood. The latter measure knocks out Pluto and 2003UB313 (Eris) which orbit among the icy wrecks of the Kuiper Belt, and Ceres which is in the asteroid belt.
No spacecraft have yet visited Pluto, however NASA has launched a mission called New Horizons that will explore both Pluto and the Kuiper Belt region. Pluto is covered with methane ice and surface temperature is -230 degrees C. Picture shows Pluto's Surface from 3 Billion Miles. Images of Pluto taken by the NASA Hubble Space Telescope with the ESA Faint Object Camera.
