Apparently while Hubble was doing a survey of Pluto to determine if it had rings like Saturn or Uranus they discovered instead that Pluto has another moon. This discovery is based on the continuing work of the New Horizons mission. The New Horizons mission will be doing a close flyby in 2015. With this new discovery program managers can work to include a study of the new moon.
The new moon is located between the orbits of Nix and Hydra, which Hubble discovered in 2005. Pluto’s other moon Charon was discovered by the US Naval Observatory in 1978 and was first imaged by Hubble in 1990.
The moon temporarily designated P4 was first imaged on June 28th by Hubbles Wide Field 3 and follow up images on July 3 and 18 confirmed the find.
The new moon is the smallest discovered around Pluto. It has an estimated diameter of 8 to 21 miles (13 to 34 km). By comparison, Charon, Pluto’s largest moon, is 648 miles (1,043 km) across, and the other moons, Nix and Hydra, are in the range of 20 to 70 miles in diameter (32 to 113 km).