BALTIMORE – Pluto has three moons, not one, new images from the Hubble Space Telescope (search) suggest. Pluto, discovered as the ninth planet in 1930, was thought to be alone until its moon Charon (search) was spotted in 1978.
The new moons, more than twice as far away as Charon and many times fainter, were spotted by Hubble in May.
While the observations have to be confirmed, members of the team that discovered the satellites said Monday they felt confident about their data.
"Pluto and Charon are not alone, they have two neighbors," said Hal Weaver of the Johns Hopkins University Applied Physics Laboratory (search).
Follow-up observations by the Hubble are planned in February. If they are confirmed, the International Astronomical Union (search) will consider names for the objects.
Earlier this month another group of astronomers, who claim to have discovered the 10th planet in the solar system, also said that body had a moon. (Whether the group actually discovered a new planet has not been confirmed.)
Both Pluto and the new, so-called planet are found in the Kuiper Belt (search), a disc of icy bodies beyond Neptune.
In fact, about a fifth of the objects observed in the region have been found to have satellites, and the percentage could grow as more are found, said Keith Noll, an astronomer at the Baltimore-based Space Telescope Science Institute (search).
The institute coordinates use of the orbiting telescope, but Noll wasn't part of the Pluto team. He believes Pluto team's finding is convincing.
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 (search) in Boulder, Colo.
The jury is still out on the impact additional moons will have on the ongoing debate over whether Pluto is actually a planet.
While having a moon is a not a criteria — Mercury and Venus are moonless — 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.