Saturn’s retinue: 60 and counting

Astronomers have discovered yet another satellite of Saturn, bringing to 60 the number of moons around the ringed planet. The Cassini spacecraft spied the roughly 2-kilometer-wide body in images taken May 30.

Residing 197,700 km from Saturn, the moon orbits between Methone and Pallene, two 4-km-wide moons that were discovered by the craft soon after its arrival in July 2004. The grouping of these three objects suggests that they might be either the leftovers of a collision or a collection of icy objects that failed to coalesce into a larger moon, says Cassini scientist Carl Murray of Queen Mary, University of London.

After spotting the newest moon, temporarily known as S/2007 S4, astronomers searched through old images and found that Cassini had recorded the moon on several occasions over the past 3 years.

The moon, along with Methone, orbits Saturn in lockstep with a larger satellite, Mimas. Methone and S/2007 S4 probably didn’t initially have the orbits that they do now but fell under the influence of Mimas as gravitational tides exerted by Saturn caused the two small bodies to drift toward the large satellite, says Murray.

NASA is considering extending Cassini’s mission, scheduled to end in the summer of 2008. If the mission continues, Cassini’s orbit will take it within 7,300 km of S/2007 S4 at the end of 2009, enabling the craft to better study the moon’s composition and size. NASA released details on the newly detected body July 19.

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