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Cassiniís fast and furious orbits around Saturn continue with the 9.6-day long Rev67, the spacecraftís 68th orbit of the Ringed Planet. Unlike the last few quiet orbits, which have focused primarily on Saturnís rings, Cassiniís slate of observations for Rev67 includes a flyby of Titan and sequences involving Tethys, Enceladus, and Saturnís atmosphere, rings, and small satellites. Cassini begins Rev67, on May 5 at its farthest distance from Saturn, called apoapsis. At this point, Cassini is 1.48 million km (917,000 mi) from Saturn. The high inclination of this orbit allows for detailed study of Saturnís ring system and northern hemisphere from far above the ring plane. On May 5 and 6, Cassini performs several observations of Saturnís small satellites. These observations are designed to study the orbits of these objects and how they might evolve over short periods due to perturbations from the other satellites in the system. On May 6, Cassini will observe the northern hemisphere of Saturn, focusing on cloud formations and jets in the region. The Composite Infrared Spectrometer (CIRS) will also observe the north polar region during this 21.5-hour-long observation. On May 10, Cassini reaches periapse, its closest point to Saturn on Rev67. At that point, Cassini will be 259,000 km (161,000 mi) from Saturnís cloud tops. At periapse, Cassini will perform a non-targeted flyby of the icy satellite Tethys with a closest approach distance of 149,000 km (93,000 mi). Two observation sequences are planned for this encounter. During the first, Cassini will be 165,000 km (103,000 mi) from Tethys and (with the CIRS team controlling spacecraft pointing) will observe the southern sub-Saturn hemisphere of the satellite. This includes an excellent view of the large canyon system Ithaca Chasma and the large impact basin Telemus. A half-day later, Cassini will again observe Tethys, this time from 475,000 km (295,000 mi) over the southern leading hemisphere.
Also on May 10, Cassini will acquire two high-resolution narrow-angle camera scans of the Saturnian ring system: a radial scan of the ringsí sunlit side from the outer F ring to the inner D ring and a 300-degree azimuthal scan of the F ring (a similar mosaic, PIA08412 was recently released). Finally, Cassini will observe ringlets in the C ring. The next day, Cassini will observe the B ring near the morning shadow boundary in order to look for forming spokes and to observe the outer B ring on the right-side ansa. Cassini will also observe Enceladus from a distance of 737,000 km (458,000 mi) in order to acquire color spectroscopy. Cassini encounters Titan for the 44th time on May 12, the first flyby since late March, with a closest approach distance of only 1,000 km (602 mi). This flyby (known as T43) will allow for imaging of the trailing hemisphere of Titan, centered northwest of the bright region named Adiri, however the flyby will primarily focus on observations by RADAR and CIRS. Inbound to the encounter, when Cassini will observe Titan at high phase angles over western Fensal-Aztlan, the Imaging Science Subsystem (ISS), Visual and Infrared Mapping Spectrometer (VIMS), and CIRS teams trade control of spacecraft pointing (taking turns being ďprimeĒ) until five hours before the encounter, when RADAR will take over. RADAR will map Titanís sub-Saturn hemisphere using its radiometry modes for three hours, measuring surface properties such as roughness across this region. RADAR will also acquire a high-altitude SAR swath over the western part of Tui Regio, an area of bright terrain in southwestern Xanadu. ISS and VIMS observations of Tui Regio from earlier in the mission suggest that this feature is compositionally distinct and may have been created from cryovolcanic activity.
The RADAR team will be in control of spacecraft pointing during Cassiniís closest approach to Titan. RADAR will acquire a full SAR swath that runs from southeast to northwest--starting southwest of Hotei Arcus across central Xanadu, to northern Shangri-la, across central Dilmun, and finally ending north of western Adiri. Among the highlights from this swath is Tortola Facula, a bright feature in northern Shangri-la that was observed at a resolution of 2 km (1.2 mi) per pixel by VIMS during the first Titan flyby. The VIMS team has suggested that this feature may be a cryovolcano, although it is not compositionally distinct like other hypothesized cryovolcanic features such as Tui Regio, Hotei Arcus, and Omacatl Macula. The higher resolution of RADAR may be able to resolve this question. The RADAR swath will also cross a hypothesized large impact basin that may cover much of Xanadu. Finally, RADAR will also acquire altimetry swaths near Hotei Arcus and within the bright terrain north of Belet.
Following closest approach, CIRS will control spacecraft pointing, acquiring numerous temperature maps and limb compositional profiles. ISS and VIMS will ride along.
Cassini begins the following orbit, Rev68, on May 14. Rev68 includes distant observations of Tethys, Dione, and Janus.