April 7, 2010
Cassini swoops down to within about 500 kilometers (311 miles) of Dione to "sniff" the moon. Particle and fields instruments will try to determine if Dione is actively spewing particles.
The Composite Infrared Spectrometer (CIRS) begins observations on the approach to this Dione flyby by making a map of the satellite while Dione is in Saturn's shadow, so the heat from the sun is not measured, but any heat from Dione is gauged. The Ultraviolet Imaging Spectrograph (UVIS) and Visible and Infrared Mapping Spectrometer (VIMS) will also image Dione. The Cassini Plasma Spectrometer then takes control for closest-approach to observe the interaction between Dione and Saturn's magnetosphere, with most of the other instruments also taking data. UVIS then will map Dione's surface albedo in ultraviolet to measure composition, while other Optical Remote Sensing instruments are observing the terrain. The Imaging Science Subsystem (ISS) follows UVIS to do a 20-panel mosaic with the other remote sensing instruments also taking data, to get compositional, thermal and geological information about Dione's sub-Saturnian hemisphere.