Dione 'D-3' Flyby: What Lies Beneath?
On Dec. 12 the Cassini spacecraft flew by Dione at about 61 miles (99 kilometers) to examine the moon's internal structure. The radio science measurement should add insight into how highly structured the center of the small moon is, which in turn should provide clues about its recent history and possible activity.
The design of this close encounter provided the ion and neutral mass spectrometer (INMS) a good sample opportunity, and before closest approach there was also time for the optical remote sensing (ORS) instruments to observe Enceladus in the near-distance. Then, with the composite infrared spectrometer (CIRS) in the lead, Cassini turned back to Dione to study the moon's icy surface fractures and search further for signs of activity.
On the outbound leg, the imaging science subsystem (ISS) lead for ORS instruments to map Dione with a mosaic. There was also an opportunity for a scan for the composite infrared spectrometer (CIRS) and a long observation for the visible and infrared mapping spectrometer (VIMS).