CICLOPS: Cassini Imaging Central Laboratory for OPerationS

Rev 52: Nov 5 - Nov 25 '07
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Cassini's journey at Saturn continues with Rev 52, its 53rd orbit of the ringed planet. Cassini's slate of observations this orbit include a flyby of Titan, numerous observations of Saturn's atmosphere and faint rings, and a eclipse of the Sun by Saturn.

Cassini begins Rev52, on November 5 at its farthest distance from Saturn, called apoapsis. At this point, Cassini is 2.99 million km (1.86 million mi) from Saturn. The first week of Rev52 is filled with observations of Saturn's atmosphere. During the first five days, daily observations are planned of Saturn's atmosphere to observe cloud motions and convection. The last few orbits have provided an opportunity to observe Saturn at low phase angles around apoapsis. Observing cloud features in Saturn's northern hemisphere over several orbits will provide a better understanding of winds in the upper atmosphere in a region that has come out of the shadow of the rings in the last few years.

Several observations of the F and G rings occur between November 11 and 14. The observations are designed to study the sizes of the particles that make up these two faint rings. Such studies are performed by measuring the brightness of a ring at different phase angles--whether the Sun is behind the spacecraft, to the left or right of the spacecraft, or in front of it with respect to the ring in question. The brightness of a ring can change at different phase angles, depending on the size of the particles that make up the ring. These observations are interspersed with imaging of small satellites in order to further refine knowledge of the moons' orbits.

Several non-targeted satellite observations are planned for November 15 and 16. The first is a distant observation of Enceladus, from a distance of 970,000 km (603,000 mi), designed to help reveal the surface properties of that satellite's trailing hemisphere (see PIA08353 for a much higher resolution view of this region). On November 16, Cassini performs a non-targeted flyby of Saturn's pockmarked moon, Rhea, at a distance of 90,600 km (56,300 mi). The closest observations from this encounter will be acquired at a distance of 313,000 km (195,000 mi). These images will be acquired while Rhea is in a crescent phase as seen from Cassini and will provide high-phase-angle observations of the large impact basins, such as Tirawa, on Rhea's anti-Saturnian hemisphere.

Cassini reaches periapse, the closest point in its orbit, on November 17 when it is 229,000 km (142,000 mi) above Saturn's cloud tops. Shortly before periapse, Cassini will observe Enceladus once again, from a distance of 168,000 km (104,000 mi). Only a thin crescent of Enceladus' surface will be sunlit from Cassini's perspective, but it will provide an excellent opportunity to monitor the plume erupting from the satellite's south polar region (see PIA08386 for a similar observation). Following this opportunity, Cassini turns its attention to a solar eclipse by Saturn. During a similar eclipse last year, Cassini acquired a large mosaic of the entire Saturn system (see PIA08329). This time, Cassini is much closer to Saturn and focuses its attention on the times when the Sun is just going into and out of eclipse. These observations can provide information on the structure of Saturn's upper atmosphere.

Shortly after the eclipse, Cassini will observe Anthe, a small satellite orbiting between Mimas and Enceladus, which was discovered earlier this year by the Cassini Imaging Team. This observation will allow for a more refined estimate of the satellite's size and orbit.

Cassini encounters Titan for the 38th time on July 19, with a closest approach distance of only 1,000 km (621 mi). Like many of the encounters this year, the flyby (known as T37) will allow for imaging of the trailing hemisphere of Titan, centered around the bright region named Adiri. Inbound to the encounter, the Composite InfraRed Spectrometer (CIRS) and Visual and Infrared Mapping Spectrometer (VIMS) teams control spacecraft pointing (they are said to be "prime"). These observations of Titan's night side will provide information on the composition of the giant moon's hydrocarbon-rich atmosphere. The same goes for the Ion and Neutral Mass Spectrometer (INMS) during closest approach, when it will directly sample the composition of Titan's upper atmosphere. Outbound from Titan, Cassini's Imaging Science Subsystem (ISS) and VIMS will observe Titan's trailing hemisphere around Adiri. The highest resolution observations are planned for the region surrounding the Huygens probe's landing site and the region to the northwest of Adiri. Near the end of the encounter, CIRS will create a temperature map of various levels in the atmosphere and look at the atmosphere's composition.

During the last week of Rev52, Cassini will perform two observations of the E ring in the region between Mimas and Enceladus, as part of a campaign to measure the photometry of the faint rings of Saturn. In addition, Cassini will observe Iapetus on November 24 from a distance of 1.4 million km (870,000 mi).

Cassini begins the following orbit, number 54 ("Rev53"), on November 25, during which it will encounter Titan for the 39th time and fly by the inner satellite, Epimetheus.

Image products created in Celestia.

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