Skip Navigation: Avoid going through Home page links and jump straight to content

New Saturn Moon Discovered


NASA Press Release
July 1990


A new moon orbiting planet Saturn has been discovered by Dr. Mark Showalter, a researcher at NASA's Ames Research Center, Mountain View, Calif. Showalter found the small, bright object while analyzing images taken by the Voyager 2 spacecraft. "It was very gratifying to see it," he said. Showalter used a computer program he wrote to sort through 30,000 images sent back to Earth during the Voyager/Saturn encounters in 1980-81.

When the discovery is certified by the International Astronomical Union (IAU), it will bring to 18 the number of Saturnian moons. The new moon has a diameter of only 12 miles and is temporarily designated 1981S13. It orbits in the major gap, known as Encke's gap, in Saturn's outermost major ring, the "A" ring. A wavy pattern in the ring material on both sides of Encke's gap was first noticed by Ames' ring expert Dr. Jeff Cuzzi while studying basic ring structure in the mid-1980s. Adapting a theory from galactic dynamics, he and Dr. Jeffrey Scargle, also at Ames, suggested that the disturbance was caused by an unseen asteroid-sized moon in the gap.

Showalter further analyzed the disturbance and used this "moonlet wake" pattern, resembling a motorboat wake, to determine the position and mass of the unseen body. The amplitude of the waves, he said, suggested the mass of the unobserved object and the wavelength of the ripples revealed the moon's possible position.

Showalter's computer program combined information on the Voyager spacecraft's position and camera direction with his prediction of the orbit to search through the enormous stock of Voyager imagery and select the frames where the moon would fall in the camera's field of view.

Brian Marsden of the IAU contacted Showalter saying, "I congratulate you on this modern-day repetition of the discovery of Neptune. It's a nice piece of work." Planet Neptune also was first predicted by theorists who observed its gravitational influence on Uranus before sighting it in 1846.

Showalter's research is supported by the Ames Space Science Division under a joint agreement with Stanford University. He is a research affiliate at the Stanford Center for Radar Astronomy.

saturn_home.gif Saturn Ring Plane Crossing Home Page

Please direct questions and comments about this Home Page to
Ron Baalke