Tiny, frozen Pluto adds to its moon family

  • World
  • Thursday, 23 Feb 2006

LONDON (Reuters) - The tiny, distant and frozen planet Pluto, for 30 years believed to have just one moon, has suddenly been found to have two more satellites. 

Only discovered in 1930 because of its vast distance from Earth, Pluto has remained a largely enigmatic object ever since. 

Some three billion miles from the Sun, Pluto, the ninth planet, is the only one not yet to have been visited by a spacecraft. 

Its first known satellite Charon was not discovered until 1978. With a diameter of 1,200 km, it is half that of Pluto -- abnormally large for a moon in relation to its primary. 

But now, using images from the Hubble Space Telescope, scientists from Johns Hopkins University, Southwest Research Institute and the Massachussetts Institute of Technology say they have found two more tiny orbiting satellites, P1 and P2. 

Both are travelling outside the orbit of Charon and are tiny by comparison, the scientists wrote in the journal Nature. 

P1, the more distant of the two from Pluto, has a diameter of between 60 and 165 km while P2 is 20 percent smaller. 

"Although definitive orbits cannot be derived, both new satellites appear to be moving in circular orbits in the same orbital plane as Charon with orbital periods of about 38 days for P1 and 25 days for P2," they wrote. 

The discovery of the two new members of Pluto's family make it the only object in the Kuiper Belt -- a vast region of rock and ice beyond Neptune which contains debris from the formation of the solar system -- known to have multiple satellites, the scientists said. 

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