Astronomers have detected a new, fifth moon orbiting the dwarf planet Pluto, using images taken with the Hubble Space Telescope (above).
The irregularly shaped moon is between six and 16 miles across. It circles Pluto in a 30,000-mile-radius orbit, roughly an eighth of the distance at which our moon orbits Earth. Hubble spotted the moon, whose short designation is "P5," with one of its wide-field cameras in nine images taken in late June and early July.
The moon appears to lie in the same plane as the other four moons, which orbit in neat concentric circles that planetary astronomer Mark Showalter of the SETI Institute likened to Russian dolls.
According to theory, the moons were formed billions of years ago when Pluto smashed into a large object in the Kuiper belt, a part of the outer solar system containing many small, icy objects. Hubble's new find could provide scientists with more information to explain how Pluto and its moons formed.
The largest moon of Pluto, Charon, was discovered in 1978 by the United States Naval Observatory station in Flagstaff, Arizona, back when Pluto was still called a planet. The next two moons, Nix and Hydra, weren't discovered until 2006, using Hubble. The fourth moon, given the less sexy name P4, was discovered with Hubble in 2011.
While Hubble provides only a distant glimpse of Pluto and its moons, NASA's New Horizons space probe is currently speeding out to Pluto. The spacecraft should arrive in 2015, when it will take the first detailed photos of the icy dwarf planet system. The discovery of the fifth Pluto moon will help scientists prevent a collision that might destroy New Horizons, which will be zooming by at 30,000 mph.
Later on, astronomers will use the James Webb Space Telescope, which is planned to succeed Hubble, to study the surface chemistry of Kuiper Belt objects, including Pluto and its moons.
