Cassini discovers Saturn moon atmosphere

March 19, 2005 NASA's Saturn exploration spacecraft, Cassini, has discovered an atmosphere about the moon Enceladus. This is the first such discovery by Cassini, other than Titan, of the presence of an atmosphere around a Saturn moon.

Enceladus's gravity is too weak to hold an atmosphere around the planet, leading scientists to believe that volcanism, geysers, or gases escaping from the surface or the interior as a continuous source for the atmosphere.

The atmosphere was detected using a magnetometer during two close flybys of Enceladus on February 17 and March 9. The magnetometer is used to measure the magnitude and direction of magnetic fields surrounding Saturn and its moons. The magnetometer detected a bending of Saturn's magnetic field around the moon, indicating the Saturnian plasma is being diverted away from an extended atmosphere. The observations from the Enceladus flybys are believed to be due to ionized water vapor.

"These new results from Cassini may be the first evidence of gases originating either from the surface or possibly from the interior of Enceladus," said Dr. Michele Dougherty, principal investigator for the Cassini magnetometer and professor at Imperial College in London.

Scientists have suspected Enceladus as geologically active and a possible source of Saturn's icy E ring. Enceladus is the most reflective object in the solar system, reflecting about 90 percent of the sunlight that hits it. Cassini first arrived in Saturn orbit July 1, 2004, releasing the Huygens Titan probe on December 25, 2004 which landed on Titan January 14, 2005.

The Cassini-Huygens mission is a cooperative project of NASA, the European Space Agency and the Italian Space Agency. The Cassini orbiter was designed, developed and assembled at the Jet Propulsion Laboratory in Pasadena, California.