During a busy first year in orbit around Saturn, the Cassini spacecraft got its first close-up look at the ringed planet’s sixth-largest moon, Enceladus—and wowed scientists in the process. The spacecraft discovered a significant atmosphere, evidence that water may lurk beneath the surface, and clues that Enceladus (pronounced en-SELL-uh-dus) may currently contain active volcanoes.
The 310-mile-wide moon (right) has long been interesting because of its landscape, marked by cratered plains and a complex network of surface cracks (left). The latest images, which show fractures up to several miles wide, all but confirm that the moon was geologically active in the past. During Cassini’s two close Enceladus flybys this spring, its Visual Infrared Mapping Spectrometer detected strong signatures in Saturn’s magnetic field around the moon. Scientists believe some sort of gas escaping from either the surface or the interior of the moon must be causing these perturbations.
The probable scenario, says Marcia Burton, a Cassini magnetometer team member, is that the moon has a persistent atmosphere that has until now gone undetected. As for a source of the gases, scientists are still looking for answers. “We don’t have anything conclusive yet, but we’re going to continue to look for evidence of [volcanic] outgassing or geysers,” says Carolyn Porco, lead scientist on Cassini’s imaging team.
Two more flybys of Enceladus are currently planned, one next month and one in March 2008. “Insofar as there might be a soft, waterlike interior—or water actually in the interior—Enceladus is the [Saturnian satellite] that is most probable for that scenario,” says Porco. “It is definitely a mystery moon.”