Astronomers using the Hubble Space Telescope to plot a safe course past Pluto for the New Horizons spacecraft have discovered a fifth moon orbiting the distant dwarf planet.
Designated P5 in the image below, and more formally known - provisionally -- as S/2012 (134340), the planet appears to be an irregular object six to 15 miles across, in a circular orbit 58,000 miles in diameter.
NASA: ESA; M. Showalter, SETI Institute
If P5 holds up as a Pluto moon, the Hubble instrument can claim the discovery of four moons orbiting the icy object that New Horizons will visit in 2015. The U.S. Naval Observatory discovered Charon, the largest, in 1978, and the Hubble found the smaller moons Nix and Hydra in 2009, and P4 last year.
P5 showed up in nine sets of images collected by the Hubble's Wide Field Camera 3 between June 26 and July 9.
"The discovery of so many small moons indirectly tells us that there must be lots of small particles lurking unseen in the Pluto system," stated Harold Weaver of the Johns Hopkins University Applied Physics Laboratory, a member of the team scouting Pluto for New Horizons.
At 30,000 mph when it flies past Pluto, an object the size of a BB-shot could destroy the spacecraft, NASA believes.
"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, " stated Alan Stern of Southwest Research Institute, the mission principal investigator.
It will also help scientists understand better how the Pluto system formed. Right now the best guess is that the moons are left over from a collision between Pluto and another large Kuiper Belt object billions of years ago.