Pluto's moons

The Hubble Space telescope has discovered a fifth moon, circled and labeled P5, orbiting dwarf planet Pluto. (NASA / July 11, 2012)

Pluto may not be a full-fledged planet, but it has five moons, astronomers have discovered.

The fifth one is 6 to 15 miles wide and circles the dwarf planet in a 58,000-mile orbit, according to a research team that includes one scientist at the Johns Hopkins Applied Physics Laboratory in Laurel.

The moon is, for now, being called S/2012 (134340) 1. It was detected in nine separate sets of images taken by the Hubble Space Telescope's Wide Field Camera 3 since June 26.

The fact that a dwarf planet like Pluto can have so many moons is intriguing to scientists, according to NASA officials.

"The discovery of so many small moons indirectly tells us that there must be lots of small particles lurking unseen in the Pluto system," said Harold Weaver, of the Hopkins APL.

Pluto's largest moon, called Charon, was detected in 1978. Two more, Nix and Hydra, were found in 2006, and the fourth, P4, was found in 2011.

The Hubble was scouting the area around Pluto ahead of NASA's New Horizons spacecraft, which launched in 2006 is slated to fly through and explore the Pluto system in 2015. Astronomers also plan to explore Pluto more using Hubble's planned successor, the James Webb Space Telescope.

An earlier version of this post misstated the launch timing for New Horizons.

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