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Last Updated: Tuesday, 1 November 2005, 14:01 GMT
Two new moons found around Pluto
The two new moons are circled in red, alongside Pluto (white) and Charon (blue)
The Hubble Space Telescope has spotted two possible new moons around Pluto, the ninth planet in the Solar System.

If confirmed, it would bring Pluto's tally of satellites to three; Charon, the only known moon of Pluto, was discovered by astronomers in 1978.

Confirmation of two new moons would shed light on the evolution of the Kuiper Belt, the vast region containing icy objects beyond Neptune's orbit.

All the candidate moons seem to orbit Pluto in an anti-clockwise direction.

The candidate moons, given the provisional names S/2005 P1 and S/2005 P2, are between 45 and 160km (30 and 100 miles) across. By comparison, Charon's diameter is about 1,200km (745 miles).

Observations suggest they orbit Pluto at at least twice the distance Charon does. P2 stays about 49,000km (30,000 miles) from the planet; P1 lies even further away at 65,000km (40,000 miles).

Fainter objects

Hubble's Advanced Camera for Surveys instrument observed the two new candidate moons on 15 May.

"The new satellite candidates are roughly 5,000 times fainter than Pluto, but they really stood out in these Hubble images," said Max Mutchler, of the Space Telescope Science Institute in Baltimore, and the first team member to identify the objects.

Artist's impression of the Pluto system, Nasa/Space Telescope Science Institute
Pluto resides beyond Neptune in the region known as the Kuiper Belt
Three days later, Hubble looked at Pluto again. The two objects were still there and appeared to be moving in orbit around Pluto.

"A re-examination of Hubble images taken on 14 June 2002 has essentially confirmed the presence of both P1 and P2 near the predicted locations based on the 2005 Hubble observations," added Marc Buie, of the Lowell Observatory, Flagstaff, Arizona, another member of the team.

The discovery would make Pluto the first Kuiper Belt object known to have more than one satellite.

The team behind the discovery plans to make follow-up observations in February to confirm the objects really are new moons of Pluto.

Only then can the International Astronomical Union, consider names for the candidate satellites.

The researchers also looked for other potential moons around Pluto.

"These Hubble images represent the most sensitive search yet for objects around Pluto," said Andrew Steffl, of the Southwest Research Institute, Boulder, Colorado.

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Farewell Pluto?
02 Aug 05 |  Magazine
Pluto's moon lines up for science
27 Jul 05 |  Science/Nature

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