Size comparison between the Earth, Moon, Pluto and 2004 DW (Click for larger view/Google photo)

BEIJING, Nov. 1 -- Pluto, discovered as the ninth planet in the solar system in 1930, may have three moons instead of one, scientists announced on Monday.

    Pluto's first known moon, Charon, was discovered in 1978 , in orbit about 12,000 miles from the planet. But until yesterday's announcement, neither Pluto nor any other object in the Kuiper Belt, a region of icy, rocky objects orbiting in the far reaches of the solar system, was known to have multiple companions.

    The two new moons were spotted in May by astronomers using Hubble to size up potential targets for investigation by NASA's New Horizons mission, scheduled to be launched early in 2006 on a multiyear expedition to Pluto and the Kuiper Belt.

    "Pluto and Charon are not alone, they have two neighbors," said Hal Weaver of the Johns Hopkins University Applied Physics Laboratory.

    Weaver said Pluto would be the first Kuiper belt object found to have multiple satellites. Depending on how reflective the surface of the moons are, the newly found moons are estimated to be between 30 and 100 miles across, he said.

    Further observations of Pluto and the two new bodies will help astronomers more accurately determine the mass and density of Pluto and its large moon Charon, said team member Alan Stern of the Southwest Research Institute in Boulder, Colo.

    However, the new finding does little to clear up Pluto's planetary status. While it was discovered in 1930, Pluto has such an eccentric orbit around the sun that some have questioned whether it deserves to be called a planet.

    The International Astronomical Union calls it a planet, but the specific definition of what constitutes a planet is under review.

    While having a moon is a not a criteria ¡ª Mercury and Venus are moonless ¡ª having more can't hurt, Stern said.

    "Just on a visceral level, the fact that Pluto has a whole suite of companions will make some people feel better," Stern said.

    (Agencies)