New moon found orbiting demoted dwarf planet Pluto

The moons of Pluto as scientists thought of them in 2006, when the Hubble telescope picked out the third and fourth moons. (NASA, ESA, H. Weaver (JHU/APL), A. Stern (SwRI))

July 7, 2012: NASA's Hubble Space Telescope has captured an image showing five moons orbiting the distant, icy dwarf planet Pluto. The green circle marks the newly discovered moon, designated P5. (NASA, ESA, and M. Showalter)

A fifth moon has been discovered orbiting former planet Pluto, scientists with the Hubble Space Telescope announced Wednesday -- but it’s still not enough to bump the dwarf planet back into the big leagues.

"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 scheduled to fly by the Pluto system in 2015, according to Space.com. That will be the first mission ever to visit Pluto.

Just don’t call it a planet.

In 2006, the International Astronomical Union sent Pluto down to the minor leagues, labeling what had been the ninth planet orbiting our sun a “dwarf planet” instead. In spite of its many moons -- including the new one, tentatively named P5 -- Pluto has more in common with the other icy asteroids and planetoids orbiting with it in the "Kuiper Belt" beyond Neptune, the IAU said, than with Saturn, Uranus and Earth.

"[Pluto's] 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.

So five moons later, Pluto’s still not a planet -- though it is a very complex system. Scientists believe the many moons are relics of a collision between Pluto and another large object billions of years ago.

P5 joins Charon, Nix, Hydra, and P4 in orbit around the dwarf. It’s estimated to be irregular in shape and 6 to 15 miles across. It is in a 58,000-mile-diameter circular orbit around.

"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 Johns Hopkins University Applied Physics Laboratory.

Or should they be called dwarf moons?