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Cassini continues its series of seven-day-long orbits with Rev88, the spacecraftís 89th orbit around the Ringed Planet. During Rev88, Cassini will perform its third targeted flyby of Enceladus this year, with one more coming up later this month.
(See the special Enceladus Rev88 Looking Ahead feature for more details about the Oct. 9 encounter.) Cassini begins Rev88 on October 6 at its farthest distance from Saturn, called apoapsis. At this point, Cassini is 1.21 million km (756,000 mi) from Saturn. Like most of the orbits during 2008, Cassini is at a high-inclination, providing opportunities to view the ring system from high above the ring plane. Such an orbit provides views of the polar regions of Saturn and its satellites. Cassini ISSís first observation of Rev88 covers Saturnís narrow F ring. This observation is designed to monitor channels and streamers generated in the ring by the close passage of Prometheus.
On October 7 and 8, Cassini turns its cameras to Titan, hoping to monitor clouds on that satelliteís northern trailing hemisphere, particularly near Kraken Mare, Titanís largest methane sea. Cassini ISS has imaged Titan on several occasions during the last few orbits, searching for clouds and keeping an eye out for possible surface changes. Unfortunately, clouds have only been observed in one of the observations, over the northern leading hemisphere. Clouds were observed on several occasions last year, off the southeast coast of the Kraken.
On October 7, Cassini will observe several of Saturnís small, inner satellites as part of the imaging teamís orbit determination campaign. On October 8, Cassini will turn its cameras to Saturnís north polar region, allowing the Ultraviolet Imaging Spectrometer (UVIS) to observe Saturnís Aurora Borealis. On October 9, Cassini will perform a targeted encounter with Enceladus, its third of the year, and the sixth thus far in Cassiniís mission at Saturn. During the encounter, Cassini reaches periapse, its closest point to Saturn on Rev88. At that point, Cassini will be 237,537 km (147,599 mi) from Saturnís cloud tops. Near periapse, Cassini will quickly pass high over the north polar region of Saturn before descending below the ring plane 38 minutes before periapse. Before the encounter begins, Cassini will turn its cameras for two distant observations of Enceladus. The first, designed by the ISS team, will look at the moonís south polar plume in an attempt to measure the current particles flux. The team to compare these measurements to the direct measurements made by Cassiniís fields-and-particles instruments during the flyby. Shortly afterward, UVIS will perform a similar measurement from high above the moonís north polar region. A detailed summary of the encounter is available here.
After the flyby, Cassini will once again turn its remote-sensing instruments to Tethys and Enceladus. First, Cassini will observe the southern sub-Saturn hemisphere of Tethys from a distance of 400,000 km (249,000 mi). Then, Cassini will turn its cameras back to Enceladus for one more UVIS observation of the south polar region.
On October 11, Cassini ISS focuses on a variety of targets. First, Cassini will acquire a time-lapse movie of the outer Cassini Division. Next, it will observe Titanís sub-Saturn hemisphere at a very low phase angle, from a distance of 2.22 million km (1.38 million mi). Finally, Cassini will turn back to the ring system to observe spokes in the B ring.
On October 12, Cassini will perform several distant observations of Saturnís icy satellites. Many of these observations are designed to allow imaging scientists to study the surface properties of these moons. Targets for these photometry observations include the leading hemispheres of Tethys and Dione. Cassini will also perform two orbit determination observations of some of Saturnís small, inner satellites. In addition to all of these moon sequences, Cassini will also observe the F ring as part of its montioring campaign of that narrow ring.
Cassini begins Rev89 on October 13. Before Cassini closes the door on this revolution, the spacecraft will again observe several of Saturnís satellites. First, Cassini will acquire a distant observation of the leading hemisphere of Rhea. Next up are more orbit-determination images of the small, inner moons. Finally, Cassini will observe the small, outer moon Ymir from a distance of 18.7 million km (11.6 million mi). From this great distance, Ymir will appear as just a point of light.
Image products created in Celestia. Enceladus basemap by Steve Albers. Saturn basemap by BjŲrn Jůnsson. All dates in Coordinated Universal Time (UTC).