The last time Cassini flew past Saturn’s moon Enceladus (August 11), temperatures over one of the so-called ‘tiger stripe’ fractures at the south pole were lower than had been measured on an earlier flyby in March. Two October encounters, one of them scheduled for today, may provide enough additional data to help us understand what’s going on. The fracture in question is known as Damascus Sulcus, which showed temperatures between 160 and 167 Kelvin in August, but 180 degrees Kelvin during the March flyby.

Then again, nothing about Enceladus should surprise us any longer, including an apparent change in the intensity of the plume, within which trace amounts of organics have been detected. The October 9 approach takes us to a distance closer than any previous flyby of a Saturnian moon, a mere 25 kilometers from the surface, a key objective being to study the composition of the plume with the spacecraft’s field and particle instruments. Thus Tamas Gambosi (University of Michigan, Ann Arbor):

“We know that Enceladus produces a few hundred kilograms per second of gas and dust and that this material is mainly water vapor and water ice. The water vapor and the evaporation from the ice grains contribute most of the mass found in Saturn’s magnetosphere. One of the overarching scientific puzzles we are trying to understand is what happens to the gas and dust released from Enceladus, including how some of the gas is transformed to ionized plasma and is disseminated throughout the magnetosphere.”

Image: This graphic shows the trajectories for the Cassini spacecraft flybys planned for Oct. 9 (E5) and 31, 2008 (E6). During Cassini’s Oct. 9 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. Image credit: NASA/JPL.

The October 31 flyby, closing to 196 kilometers, will image the tiger stripe region again, with both encounters offering the chance to find still further changes around this deeply interesting object. With four more Enceladus flybys planned for the next two years of the Cassini Equinox Mission — the name for Cassini’s extended mission — we can hope to learn more about what powers its geysers. We may also find clues to the moon’s past, since the different isotopes found in that environment could help to identify the temperatures at work during the formation of Enceladus.

Note: NASA’s Cassini flyby blog is now active.