spacetoday.net: Fourth moon discovered around Pluto

Posted: Thu, Jul 21, 2011, 5:22 AM ET (0922 GMT)
Pluto P4 moon image from Hubble (STScI)

Astronomers using the Hubble Space Telescope have found a fourth moon orbiting the dwarf planet Pluto, they announced Wednesday. The moon, officially designated S/2011 (134340) 1 and unofficially dubbed P4, is the smallest body yet found orbiting Pluto, with a diameter of 13 to 34 kilometers. The object was spotted in a Hubble image of the Pluto system taken in late June and confirmed with follow-up observations taken as recently as Monday. It orbits between two other moons, Nix and Hydra, discovered in Hubble observations in 2005. The latest discovery, however, does not change Pluto's official status as a "dwarf planet", after the International Astronomical Union approved a new definition of the term planet in 2006 that effectively demoted what had been the solar system's ninth planet.