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Cassini continues its series of week-long orbits with Rev72, the spacecraft's 73rd orbit around the Ringed Planet. The shorter orbit lends itself to a more dedicated set of observations, including imaging of Saturn's atmosphere, rings, and several of its moons, including Mimas, Rhea, and Titan. Cassini begins Rev72 on June 12 at its farthest distance from Saturn, called apoapsis. At this point, Cassini is 1.27 million km (786,000 mi) from Saturn. On June 12 and 13, Cassini performs several observations of Saturn's small, inner 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 June 13, Cassini performs a non-targeted encounter of Titan at a distance of 365,000 km (227,000 mi). Cassini ISS will acquire a four-frame mosaic across the northern anti-Saturnian hemisphere of Titan and the region around the north pole. Previous imaging of the north pole by Cassini has revealed a large, as-yet-unnamed methane sea, in addition to the two other named seas (Kraken Mare and Ligeia Mare) a little farther to the south. The images acquired during this observation will provide a more detailed look at the unnamed lake feature and other lakes in the area, although RADAR observations of the region have revealed mostly small lakes that maybe below ISS' resolution limit.
On June 14, Cassini's wide-angle camera will acquire a 12-hour-long, 2,350-frame time-lapse movie of the unlit side of the B ring, looking for forming spokes. On June 16, Cassini reaches periapse, its closest point to Saturn on Rev71. At that point, Cassini will be 163,000 km (101,000 mi) from Saturn's cloud tops. Near periapse, Cassini will quickly pass high over the north polar region of Saturn before descending below the ring plane 15 minutes before periapse. An hour after periapse, Cassini ISS and the Composite Infrared Spectrometer (CIRS) will observe Mimas' southern sub-Saturnian hemisphere from a distance of 200,000 km (124,000 mi). Also during this observation, Cassini will slew over to image Dione with the wide-angle camera and CIRS, just as the moon is entering an eclipse by Saturn.
The next day, June 17, Cassini will observe Rhea just as it is exiting an eclipse by Saturn. Cassini will also observe several locations in the inner C ring. On June 18, Cassini ISS will acquire two, two-hour-long wide-angle camera movie sequences of Saturn's atmosphere. These observations are designed to study the photometric properties of Saturn's clouds as they rotate around from the center of the disk (from Cassini's perspective) to the limb. Cassini also makes a ringplane crossing on June 18, and will observe the space around Rhea (but not the moon itself) in an attempt to observe possible rings around this moon suspected from measurements by Cassini's Fields-and-Particles instruments.
On June 19 the spacecraft will perform a filter response calibration test on both cameras by observing the star HD 20630, a solar analog star in the constellation Cetus. These calibration images are needed to characterize possible changes in the properties of the cameras' CCD detectors. Also on June 19, Cassini ISS will observe the northern hemisphere of Saturn, investigating the dynamics of Saturn's clouds.
Cassini begins the following orbit, Rev73, on June 19. Rev73 includes distant observations of Tethys, Dione, Enceladus, and Saturn's atmosphere.
Image products created in Celestia. Rhea basemap by Steve Albers.