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Cassini continues its exploration of the Saturn system with the 8-day Rev 249, which begins on November 15 at its farthest distance from the planet. This is also called the orbit’s apoapse. At this point, Cassini is 1.26 million kilometers (0.78 million miles) from Saturn’s cloud tops. Rev 249 is the last full orbit of the second inclined phase of the Cassini Solstice Mission. During this phase, Cassini will use encounters with Titan to gradually increase the inclination of its orbit. Fourteen ISS observations are planned for Rev 249 with the majority focused on Saturn’s atmosphere.
At the start of Rev 249, ISS will continue a set of cloud tracking observations that began at the end of Rev 248 after the T124 flyby. These three observations in Rev 249 (combined with the one taken in Rev 248) will be used to track clouds over Titan’s north polar region. On November 17, ISS will ride along with three Visual and Infrared Mapping Spectrometer (VIMS) and an Ultraviolet Imaging Spectrometer (UVIS) observations of Saturn’s northern hemisphere. ISS will use these observations to track clouds as VIMS acquires mosaics and UVIS observes Saturn’s north polar aurorae. By tracking clouds, researchers can measure wind speed and wind direction at different latitudes on Saturn.
On November 19 at 08:39 UTC, Cassini will reach periapse for Rev 249 at an altitude of 157,880 kilometers (98,100 miles) above Saturn's cloud tops, between the orbits of Mimas and Tethys. During the periapse period, ISS and the rest of Cassini’s instrument suite will be focused on Saturn’s atmosphere. On November 18, ISS will ride along with a VIMS movie observation of Saturn’s northern hemisphere covering nearly one Saturn day. On November 19 at 07:33 UTC, Cassini will perform a non-targeted encounter with Mimas at a distance of 44,731 kilometers (27,795 miles). ISS will ride along with the Composite Infrared Spectrometer (CIRS) to observe Saturn’s innermost icy satellite during this encounter, taking several full-disk observations of the satellite’s northern hemisphere (along with the large impact crater Herschel) as well as a four-frame mosaic covering the anti-Saturn and trailing hemispheres. The mosaic will be acquired when Mimas is at very low phase angles around closest approach, useful for mapping color variations across its surface. Afterwards, ISS will ride along with CIRS to observe the limb of Saturn and the gap between the atmosphere and the rings, a gap that Cassini will flying into starting in April of next year. On November 20, ISS will observe a crescent Titan at a distance of 1.78 million kilometers (1.10 million miles) in order to monitor seasonal changes within Titan’s upper haze layers. Afterward, VIMS will observe a solar occultation by Saturn’s rings.
On November 21, ISS will ride along with a UVIS observation of a stellar occultation by Rhea. During this observation, Rhea will pass near the star Zeta Orionis, providing an opportunity to look for a tenuous exosphere of water vapor at Rhea. Afterward, ISS will observe the limb of Saturn. On November 22, ISS will ride along with UVIS to observe a crescent Saturn.
On November 23, Cassini will reach apoapse, bringing Rev 249 to a close, and starting up the next orbit, Rev 250, when Cassini will perform a targeted encounter with Titan to begin an exciting new phase in Cassini’s mission at Saturn: The F-ring orbits.
Image products created in Celestia. All dates in Coordinated Universal Time (UTC).