Astronomers studying the Pluto system with the Hubble Space Telescope recently discovered another moon orbiting the dwarf planet.
The new moon, Pluto's fifth, is irregular in shape and 6 to 15 miles across. It circles Pluto in a 58,000 mile-diameter orbit.
The small moon, designated P5, was detected in nine separate sets of images taken by Hubble's Wide Field Camera this summer.
The detection of the new moon will help scientists navigate NASA's New Horizons spacecraft through the Pluto system in 2015, when it makes a high-speed flyby of the dwarf planet.
The team of astronomers that made the discovery is using Hubble to search the Pluto system for potential hazards to New Horizons when it races past the dwarf planet at about 30,000 miles per hour. At this speed, a collision with even a pebble-sized piece of orbital debris could destroy the spacecraft.
Pluto was discovered in 1930 by Clyde Tombaugh, a 24-year-old amateur astronomer working at Lowell Observatory in Flagstaff, Ariz.
The dwarf planet resides 3 billion miles from the sun in the heart of the Kuiper Belt, a vast region of icy, rocky bodies beyond Neptune's orbit.
The International Astronomical Union shocked Pluto-lovers in 2006 by announcing that Pluto was no longer a planet.
Pluto's planethood was never seriously questioned until 1992. That's when astronomers starting finding other objects "out there." Pluto's neighborhood, it turns out, is cluttered with icy bodies about the size of asteroids.
In 1978, astronomers discovered Charon, Pluto's only confirmed moon until the Hubble discovery of two new moons, Nix and Hydra, in 2006. Hubble discovered another small moon, P4 in 2011.
The recent discovery of P5 provides astronomers additional clues on how the Pluto system formed and evolved. The favored theory today is that all the moons are relics of a collision between Pluto and another large Kuiper Belt object billions of years ago.