Nasa scientists have discovered another moon orbiting Pluto, measuring just 15 miles in diameter.
The P5, as it is has been temporary labelled, joins the four moons which have already been discovered: Charon, Nix, Hydra, and a fourth planet which was discovered last year and is also awaiting a permanent name.
An international team of scientists discovered the new moon while analysing images retrieved from the Hubble space telescope, which is currently providing an inventory of the Pluto system.
"The moon is in a 58,000-mile-diameter circular orbit around Pluto, that is assumed to be co-planar with the other satellites in the system", said Mark Showalter, scientist at the SETI Institute in Mountain View, California, who is leading the Hubble research project.
"The moons form a series of neatly nested orbits, a bit like Russian dolls," he added.
Four of the five moons sighted around Pluto have been discovered in the last six years. The researchers are reportedly fascinated to find out how Pluto, which is only one-fifth the size of Earth, can have such a complex collection of satellites.
Scientists also believe that the spate of recent discoveries provide additional clues to the mystery behind the formation, and composition, of Pluto. Harold Weaver, of the Johns Hopkins University Applied Physics Laboratory in Laurel, Maryland, said: "The discovery of so many small moons indirectly tells us that there must be lots of small particles lurking unseen in the Pluto system."
In 2015, Nasa's New Horizons spacecraft will make a historic high-speed fly-by of Pluto. According to Alan Stern, the mission's principal investigator, "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."