Hubble Space Telescope Spots 5th Moon near Pluto

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A tiny new moon has been discovered orbiting Pluto, scientists announced July 11.

Researchers using NASA’s Hubble Space Telescope found the moon, bringing the number of known Pluto satellites to five. The discovery comes almost exactly one year after Hubble spotted Pluto’s fourth moon, a tiny body currently called P4.

“Just announced: Pluto has some company — We’ve discovered a 5th moon using the Hubble Space Telescope!” Alan Stern of the Southwest Research Institute in Boulder, Colo., announced via Twitter.

Stern is principal investigator of NASA’s New Horizons spacecraft, which is en route to fly by the Pluto system in 2015.

Pluto’s other moons are Charon, Nix, Hydra and P4. Charon is by far the largest, measuring 1,043 kilometers across. Nix and Hydra range between 32 to 113 kilometers wide, while P4 is thought to be 13 to 34 kilometers across.

The new moon looks a lot more like P4 than like Charon.

“It’s smaller than P4,” Stern said in an interview.

“We’re finding more and more, so our concern about hazards is going up,” he added, referring to the collision risk New Horizons will face when it cruises by Pluto in a few years.

The new Pluto moon has been provisionally named S/2012 (134340) 1, though it also is going by the moniker P5. It was discovered using the Wide Field Camera 3 on the Hubble Space Telescope during a series of observations in late June and early July.

P5 appears to be irregularly shaped, with a diameter between 10 to 24 kilometers. It zips around Pluto at an average distance of 47,000 kilometers in an orbit thought to be coplanar with the dwarf planet’s other satellites, researchers said.

“The moons form a series of neatly nested orbits, a bit like Russian dolls,” said team lead Mark Showalter, of the SETI Institute in Mountain View, Calif., in a statement announcing the new moon.

Charon was first spotted in 1978, 48 years after the discovery of Pluto. Nix and Hydra were found by Hubble in 2005.

Pluto orbits 5.8 billion kilometers from the sun on average, about 39 times farther away than Earth does. For more than 75 years after its discovery, the object was regarded as a full-fledged planet, but things changed in 2006.

That year, the International Astronomical Union reclassified Pluto as a dwarf planet, since it shares orbital space with lots of other objects out in the Kuiper Belt, the ring of icy bodies beyond Neptune.

With another moon to account for around Pluto, NASA’s New Horizons mission team now is taking a fresh look at the spacecraft’s planned flyby in 2015 to make sure it will zip by the dwarf planet safely while observing the complex planetary system.

“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 New Horizons team member Harold Weaver of the Johns Hopkins University Applied Physics Laboratory in Laurel, Md.

“The inventory of the Pluto system we’re taking now with Hubble will help the New Horizons team design a safer trajectory for the spacecraft,” Stern added.