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Pluto's fifth moon: five fascinating facts (+video)

Using data from the Hubble telescope, SETI scientists spotted a fifth moon orbiting the icy dwarf planet Pluto.

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P5's discovery is exciting for researchers who study the outer solar system, but it's likely causing some of them a bit of anxiety as well.

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NASA's New Horizons spacecraft is headed to Pluto for a 2015 flyby of the dwarf planet. The detection of P5, and P4 last year, show that the Pluto system is more crowded than scientists had thought. So New Horizons may have to watch its step, since a collision with a particle as small as a BB could take the fast-moving spacecraft out.

"We're finding more and more, so our concern about hazards is going up," New Horizons principal investigator Alan Stern, of the Southwest Research Institute in Boulder, Colo., told

Stern and others are pointing Hubble at the Pluto system to get a better handle on those hazards, and the inventory they produce should help minimize New Horizons' risks, researchers said.

It may be shrapnel from a huge collision

At roughly 1,430 miles (2,300 km) across, Pluto is considerably smaller than Earth's moon. So researchers are intrigued by its complex collection of satellites.

Scientists currently think that all five of Pluto's known moons are relics of a massive collision between the dwarf planet and another large object in the Kuiper Belt — the ring of icy bodies beyond Neptune's orbit — long ago.

Follow senior writer Mike Wall on Twitter@michaeldwall or @Spacedotcom. We're also onFacebook and Google+.

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