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Cassini continues its series of seven-day-long orbits with Rev82 and Rev83, the spacecraftís 83rd and 84th orbits around the Ringed Planet. Saturn enters solar conjunction -- when the Saturnian system (including Cassini) will be nearly behind the Sun from the perspective of Earth -- on September 1. Cassini begins Rev82 on August 22 at its farthest distance from Saturn, called apoapsis. At this point, Cassini is 1.22 million km (761,000 mi) from Saturn. The first observations of the orbit for the Imaging Science Subsystem (ISS) involve Saturnís ring system. On August 23, Cassini will take a look at the F ring as part of a monitoring campaign to look for changes in the various clumps, knots, and gores in the ring caused by gravitational interactions with Prometheus, Pandora, and small clumps within the ring. The second observation targets the inner part of the Cassini Division on the ringís unlit side.
On August 26, Cassini reaches periapse, its closest point to Saturn on Rev82. 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 closest approach. During the day prior to periapse, the remote sensing instruments on Cassini, particularly the Ultraviolet Imaging Spectrometer (UVIS), will observe the north polar region of Saturn. UVIS will be observing auroral features in the region, similar to the Aurora Borealis on Earth. ISS will observe dynamical features in the upper atmosphere in the north polar region, while the Visual and Infrared Mapping Spectrometer (VIMS) will look at the dynamics of clouds deeper in Saturnís atmosphere, particularly around the North Polar Hexagon (see PIA10449). The following day, Cassiniís remote sensing instruments perform a similar observation of the south polar region and the vortex located there. On August 28, Cassini will perform another monitoring observation of the F ring, looking for new clumps and channels. Cassini will also observe Rheaís leading hemisphere from a distance of 1.4 million km (870,000 mi). During this observation Cassini will be almost directly between the Sun and Rhea, allowing the spacecraft to observe the opposition surge. Such observations can be useful in understanding the small-scale surface properties on Rhea, including particle sizes and surface roughness. On August 29, Cassini will perform a distant observation of Dione from a distance of 1.35 million km (840,000 mi). This observation will help to map color variations on Dioneís leading hemisphere. On this day Cassini will also search for small satellites between Mimas and Enceladus. This region has been a gold mine for Cassiniís moon hunters, with three new moons discovered there since 2004. Finally, on August 30, Cassini will observe various small satellites in the inner part of the Saturn system in order to better constrain their orbital motions.
Cassini reaches apoapse on August 30 and begins Rev83, its 84th orbit around Saturn. Solar conjunction begins on September 1, when the Sun will be almost directly between the Saturn System and Earth. Such an arrangement, which happens about once a year, hampers communications with the spacecraft due to interference from the solar atmosphere. To accommodate this, a more limited set of observations is planned for Rev83, mostly background fields-and-particles observations and communications tests through the antennaís Ka-band. Two imaging observations are planned for Rev83, and they are both performed right before the solar conjunction period starts. The first is a time-lapse movie sequence of the F ring, designed to monitor evolving structures generated by interactions between the ring and the various moons and clumps that orbit near the ring. The second observation, planned for September 1, will also focus the remote sensing instruments on the F ring as part of this monitoring campaign.
Cassini begins Rev84 on September 6. After solar conjunction ends on September 7, observations of Rhea, Tethys, Enceladus, Saturnís atmosphere and rings are planned.
Image products created in Celestia. Rhea basemap by Steve Albers. Saturn basemap by BjŲrn Jůnsson. All dates in Coordinated Universal Time (UTC).