NASA's Cassini spacecraft is preparing for its final flyby of the icy moon Enceladus. The pass is slated to take place on Dec. 19 at a distance of 3,106 miles (4,999 km). This final close proximity encounter of Enceladus comes as part of a farewell tour of Saturn's moons that have been so well characterized by the spacecraft, prior to beginning its "Grand Finale" mission late in 2016.

The Grand Finale will see the venerated explorer perform a series of daring maneuvers, including repeatedly diving between Saturn's innermost ring and its surface as it collects information on aspects of the gas giant, including ring mass and characterizing the ringed giant's magnetic and gravitational fields.

Compared to the previous 21 flybys of Enceladus, the closest of which took Cassini to within 16 miles (25 km) of the moon's surface, the upcoming pass will be relatively remote. This aspect of the pass is an intentional move by Cassini's handlers, designed to maximize the capabilities of the probe's Composite Infrared Spectrometer (CIRS) instrument.

During the pass, CIRS will take detailed measurements of the heat flow passing across Enceladus' south polar region, emanating from the moon's interior.

"The distance of this flyby is in the sweet spot for us to map the heat coming from within Enceladus – not too close, and not too far away" states Mike Flasar, team lead for CIRS at NASA's Goddard Space Flight Center. "It allows us to map a good portion of the intriguing south polar region at good resolution."

The heat data could potentially grant insights into the fascinating geological mechanics taking place beneath Enceladus' icy shell that work to power the moon's magnificent plumes of gas and ice.

The observations will be carried out during the southern hemisphere's winter cycle. This period creates ideal conditions for carrying out the observations, as the lack of sunlight makes it easier to detect and differentiate heat emanating from within the moon. It is expected at the end of Cassini's mission that the probe will have collected over six years worth of winter observations of the icy moon's southern hemisphere.

Source: NASA