11 New Moons Discovered Around Jupiter; Brings Total to 39

By Staff
posted: 05:15 pm ET
16 May 2002

A team of researchers announced today the discovery of 11 new moons around Jupiter, adding to nearly a dozen they found last year and bringing the total known satellites of the gas giant planet to 39.

Jupiter now has more known moons than any other planet in our solar system.

The new moons are called irregular satellites because instead of relatively circular orbits, they carve paths that are elliptically shaped and inclined with respect to the main plain where larger moons orbit Jupiter. They also orbit in the opposite direction of the planet's rotation, a motion called retrograde.

And they are small. All 11 objects are estimated to be between roughly 1.2 and 2.4 miles (2-4 kilometers) in diameter. Nothing is known about their composition, though based on experience the researchers say they are probably rocky objects similar to asteroids.

The researcher team was led by Scott S. Sheppard and David Jewitt from the University of Hawaii's Institute for Astronomy.

Of Jupiter's moons, 31 are considered irregular. The eight regular satellites include the four large Galilean moons -- Io, Europa, Ganymede and Callisto -- named for the astronomer who first spotted them in 1610 with a crude, early telescope. The other four regular satellites are smaller and orbit inside the path of Io.

Saturn, the planet with the next most satellites, has 30, of which 13 are irregular.

The odd orbits of the irregular satellites strongly suggest they were captured shortly after Jupiter's formation, the researchers say.

Jupiter's irregular moons are clustered into small families, suggesting that they may have once been parts of larger objects that broke apart. Jupiter's immense gravity might have ripped a larger object into pieces, or one object might have collided with another.

The new observations were made in December with the Canada-France-Hawaii telescope. Follow-up observations were made with the University of Hawaii 2.2-meter telescope in order to confirm the orbits.

The research team included Jan Kleyna of Cambridge University, England. Robert Jacobson at NASA's Jet Propulsion Laboratory and Brian Marsden at the Minor Planet Center also worked on the orbits to help confirm that the objects are moons of Jupiter and not asteroids travelling freely through space.