Jul 13, 2012

Fifth Moon Discovered Around Pluto

July 13, 2012: A team of astronomers using NASA’s Hubble Space Telescope has discovered another moon orbiting the dwarf planet Pluto.

They say the new moon, Pluto's 5th, is likely irregular in shape and 6 to 15 miles across. Provisionally designated S/2012 (134340) 1, it was detected in nine separate sets of images taken by Hubble’s Wide Field Camera 3 on June 26, 27, 29, and July 7 and 9.  The moon circles Pluto in a 58,000 mile-diameter orbit.

Pluto 5 (splash)
This image, taken by NASA's Hubble Space Telescope, shows five moons orbiting the distant, icy dwarf planet Pluto. The green circle marks the newly discovered moon, designated P5, as photographed by Hubble's Wide Field Camera 3 on July 7. The observations will help scientists in their planning for the July 2015 flyby of Pluto by NASA's New Horizons spacecraft. P4 was uncovered in Hubble imagery in 2011. (Credit: NASA; ESA; M. Showalter, SETI Institute)

“The moons form a series of neatly nested orbits, a bit like Russian dolls,” notes team leader Mark Showalter of the SETI Institute in Mountain View, Calif.

The Pluto team is intrigued that such a small planet can have such a complex collection of satellites. The new discovery provides additional clues for unraveling how the Pluto system formed and evolved. The favored theory is that all the moons are relics of a collision between Pluto and another large Kuiper Belt object billions of years ago. (The Kuiper Belt is a broad zone of icy Pluto-like bodies orbiting beyond Neptune. Pluto itself is considered to be a Kuiper Belt object.)

The new detection will help scientists navigate NASA’s New Horizons spacecraft through the Pluto system in 2015, when it makes an historic and long-awaited high-speed flyby of the distant world.

Pluto 5 (nh, 2000px)
A ScienceCast video previews New Horizons visit to Pluto in 2015. Play it

The team is using Hubble to scour the Pluto system to uncover potential hazards to New Horizons. Moving past the dwarf planet at a speed of 30,000 miles per hour, the spacecraft could be destroyed in a collision with even a BB-shot-size piece of orbital debris.

“The discovery of so many small moons indirectly tells us that there must be lots of small particles lurking unseen in the Pluto system,” says 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,” adds Alan Stern of the Southwest Research Institute in Boulder, Colo., the mission’s principal investigator.

Pluto’s largest moon, Charon, was discovered in 1978 in observations made at the United States Naval Observatory in Washington, D.C. Hubble observations in 2006 uncovered two additional small moons, Nix and Hydra. In 2011 another moon, P4, was found in Hubble data.

In the years following the New Horizons Pluto flyby, astronomers plan to use Hubble’s planned successor, NASA’s James Webb Space Telescope, for follow-up observations. The Webb telescope's infrared vision will be able to measure the surface chemistry of Pluto, its moons, and many other bodies that lie in the distant Kuiper Belt along with Pluto.

For more information about New Horizons and its mission to Pluto visit

Production editor: Dr. Tony Phillips | Credit: Science@NASA

More Information

Dwarf Planet Mysteries Beckon to New Horizons -- Science@NASA

New Horizons Becomes Closest Spacecraft to Pluto -- Science@NASA

Visit to Pluto -- NASA ScienceCast video

The Pluto Team members are M. Showalter (SETI Institute), H.A. Weaver (Applied Physics Laboratory, Johns Hopkins University), and S.A. Stern, A.J. Steffl, and M.W. Buie (Southwest Research Institute). -- Science@NASA

The Hubble Space Telescope is a project of international cooperation between NASA and the European Space Agency. NASA's Goddard Space Flight Center in Greenbelt, Md., manages the telescope. The Space Telescope Science Institute (STScI) in Baltimore conducts Hubble science operations. STScI is operated for NASA by the Association of Universities for Research in Astronomy, Inc., in Washington, D.C.