US: Scientists using Nasa's Hubble Space Telescope have found that Pluto has not one but three moons. The discovery is likely to prompt searches for undiscovered moons elsewhere and shed light on the evolution of the Kuiper Belt, the vast icy region of space beyond Neptune where Pluto is located.
"Pluto just became even more interesting," said Hal Weaver, a planetary scientist at the Johns Hopkins Applied Physics Laboratory in Laurel, Maryland, and co-leader of the team which made the discovery.
The newly-discovered moons are constantly being pelted by space debris, which gives Pluto an "unusual appearance", researchers say. "They should generate rings around Pluto," said Alan Stern, of the South-West Research Institute in Boulder, Colorado, the other co-leader of the team. "But, so far, no one has seen them."
"This tells us that Pluto is a much more complex world than we previously imagined," Richard Binzel, a planetary scientist at the Massachusetts Institute of Technology, said of the discovery. "How do you get so many moons around such a small planet?"
The most distant planet from the sun, Pluto is only 1,475 miles in diameter, two-thirds the size of the Earth's moon.
Moons have been discovered orbiting every planet in the solar system except Venus and Mercury. Jupiter, by far the largest planet, has 38 known moons.
Like Earth's moon, most are believed to have formed when meteors or other objects collided with the nearby planet, shooting debris into space which is gradually shaped by gravitational forces.
The new moons are 30 to 100 miles in diameter and are in orbit about 30,000 and 40,000 miles from Pluto. They take about 25 and 38 days, respectively, to complete their orbits. Charon, the moon discovered in 1978, is 12,000 miles from Pluto and orbits once every 6.4 days.
Pluto itself was discovered in 1930. Its orbit ranges from 2.7 billion miles to 4.6 billion miles from the sun. Earth is 93 million miles from the sun.