NASA’s Cassini spacecraft will fly by Saturn’s geyser moon, Enceladus. The October 9th flyby is the closest flyby yet of any moon of Saturn, at only 25 kilometers (16 miles) from the surface. The October 31 flyby is farther out, at 196 kilometers (122 miles). Scientists are intrigued by the possibility that liquid water, perhaps even an ocean, may exist beneath the surface of Enceladus. Trace amounts of organics have also been detected, raising tantalizing possibilities about the moon’s habitability. While Cassini’s cameras and other optical instruments were the focus of an August 11th flyby, during Cassini’s October 9th flyby, the spacecraft’s fields and particles instruments will venture deeper into the plume than ever before, directly sampling the particles and gases. The emphasis here is on the composition of the plume rather than imaging the surface. On October 31st, the cameras and other optical remote sensing instruments will be front and center, imaging the fractures that slash across the moon’s south polar region like stripes on a tiger. These two flybys might augment findings from the most recent Enceladus flyby, which hint at possible changes associated with the icy moon. Cassini’s August 11th encounter with Enceladus showed temperatures over one of the tiger-stripe fractures were lower than those measured in earlier flybys. The fracture, called Damascus Sulcus, was about 160 to 167 Kelvin (minus 171 to minus 159 degrees Fahrenheit), below the 180 Kelvin (minus 136 degrees Fahrenheit) reported from a flyby in March of this year.
Results from Cassini’s magnetometer instrument during the August flyby suggest a difference in the intensity of the plume compared to earlier encounters. Information from the next two flybys will help scientists understand these observations. Four more Enceladus flybys are planned in the next two years, bringing the total number to seven during Cassini’s extended mission, called the Cassini Equinox Mission. The next Enceladus doubleheader will be November 2nd and 21st, 2009. The Enceladus geysers were discovered by Cassini in 2005. Since then, scientists have been intrigued about what powers them, as the moon is so tiny, roughly the width of Arizona at only 500 kilometers (310 miles) in diameter. Scientists anticipate reporting results from the two flybys in November and early December.
