Pluto’s New Fourth Moon

With the help of NASA’s Hubble Space Telescope astronomers discovered a fourth moon orbiting the icy dwarf planet Pluto. The tiny, new satellite, temporarily designated P4, was uncovered in a Hubble survey searching for rings around the dwarf planet. 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). Pluto’s new moon is located between the orbits of Nix and Hydra. P4 was first seen in a photo taken with Hubble’s Wide Field Camera 3 on June 28. 

The moon wasn’t  seen  in earlier  Hubble  images  because the exposure  times were shorter. There is a chance it appeared as a very faint smudge in 2006 images, but was overlooked because it was obscured.
source:www.nasa.gov