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.
(CNN) -- Almost exactly one year after discovering dwarf planet Pluto's fourth moon -- though not before actually naming poor little P4 -- NASA announced Wednesday a fifth moon has been discovered orbiting the ex-planet.
Astronomers using the Hubble Space Telescope found the irregularly shaped moon, which they said measures 6 to 15 miles across. For now, it's being called P5.
"The moons form a series of neatly nested orbits, a bit like Russian dolls," said Mark Showalter of the SETI Institute in a statement released by the European Space Agency. Showalter is the leader of the scientific team that discovered the new moon.
The moon was detected in nine separate sets of images taken by Hubble's Wide Field Camera 3 on June 26, 27 and 29, and July 7 and 9, NASA says.
Pluto's other moons are Charon, Nix and Hydra.
The team at SETI Institute is "intrigued" that Pluto, deemed unworthy of planethood in 2006, could have "such a complex collection of satellites," the statement said.
The leading theory is that all the moons are remnants of a collision billions of years ago between Pluto and another large object from the Kuiper Belt -- the region of the solar system beyond Neptune.
Because Pluto is so far away from Earth, the images of P5 look like small white dots.
But a NASA spacecraft that is on its way to Pluto will give scientists better images and details about the former planet and its neighbors.
The New Horizons spacecraft was launched in 2006, just months before Pluto was demoted by the International Astronomical Union, and is now about halfway to the icy dwarf planet. It's due to fly past in July 2015.
Hubble is on a scouting mission in support of the spacecraft, and is providing valuable information to guide its flight.
"All of this stuff poses a navigation hazard for New Horizons," said Ray Villard, news director for the Space Telescope Science Institute, which operates Hubble's science mission. "It's a messy place. You have moons and perhaps small particles."
Hubble, launched into orbit in 1990, received new instruments in 2009.
"It's at the peak of its performance," Villard said.
Hubble is expected to remain operational through the end of the decade. The James Webb Space Telescope, slated for launch in 2018, will have a larger mirror and will study Pluto after the New Horizons mission.
"Finding this moon was exciting and shows us Pluto is an intriguing and complicated place," Villard told CNN.