More Moons for Saturn
Planetary scientists announce that they have found at least four new moons around Saturn, maybe more.
by Vanessa Thomas
At this year’s Division for Planetary Sciences meeting in Pasadena, California, an international team of astronomers that has already discovered five moons of Uranus in the past three years announced that they have also found four additional members of the Saturnian family. This update brings Saturn’s moon count to 22, surpassing the 21 moons orbiting Uranus as the largest batch of natural satellites known in the solar system.
On August 7, Brett Gladman of the Centre National de la Recherche Scientifique in France took a series of digital images at 1-hour intervals using the European Southern Observatory’s 2.2-meter (86.5-inch) telescope in Chile. A computer program examined the images and spotted two faint points of light moving relative to the background stars. Then on September 23 and 24, Gladman and Canadian astronomer J. J. Kavelaars used the Canada-France-Hawaii 3.5-meter (138-inch) telescope on Mauna Kea to try to recover the two objects seen in August. Not only did they find the moons again, they spotted two more. Follow-up observations by astronomers using other telescopes in Arizona and Chile soon confirmed their findings.
The four moons are thought to be at least nine million miles (15 million kilometers) from the Ringed Planet, about four times farther than our moon is from Earth. From the amount of light they reflect, the astronomers say that the moons are likely to be tiny, icy bodies between 6 and 30 miles (10 to 50 kilometers) across. Like all five Uranian satellites discovered by the team, these newfound moons are “irregular,” meaning that their orbits do not make circular hoops around the center of their host planet but are more like long ovals at odd angles.
Because irregular satellites are typically small, lie far from the planet, and have such strange orbits, planetary scientists believe that they did not form along with the planet they now orbit but were later captured by the planet’s strong gravitational pull.
Gladman and his team warn that their findings are still preliminary, although it is unlikely that these objects are asteroids or comets simply passing near Saturn. Further observations during the next several months should confidently establish the orbits as being locked around Saturn. When that is accomplished, the moons will lose their temporary designations of S/2000 S1, S2, S3, and S4 and receive names representing characters from Greek mythology.
The astronomers also revealed that various telescopes are currently tracking several other moving objects the team has spotted near Saturn. Once their positions through the sky are studied a bit longer, these objects may also prove to be additional satellites of Saturn.
Before the recent discoveries, Phoebe, discovered more than 100 years ago, was the only irregular moon known to orbit Saturn. Nine have been found orbiting Jupiter, and Neptune has two. With the four moons of Saturn and five of Uranus, the eight-member, French-U.S.-Canadian team is not only responsible for finding more irregular moons, but they have nearly doubled the number of such satellites known in the solar system.