Pluto's 4th moon

Recent Hubble images have revealed a new moon orbiting Pluto, the fourth so far discovered around the icy dwarf planet. P4 as the moon is currently known, is the smallest so far discovered at 15 to 30km across, and lies between Nix and Hydra, two small moons discovered in 2005.

Moon	Mean distance (km)	Period (d)	Year of discovery
Charon	17,540	6.387	1978
Nix	48,710	24.856	2005
S/2011 P1	~59,000	32.1	2011
Hydra	64,750	38.206	2005

The moon was unexpectedly found during an observing campaign to find rings around Pluto, which remain undiscovered. The new moon was first seen in an image taken on the 28th June and will be further studied during NASA's New Horizons mission, scheduled to fly through the Pluto system in 2015.

Links

• Astronomy Now news story
  
• Hubble Space Telescope press release