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Cassini brings in the New Year with Rev99, the spacecraft's 100th orbit around the Ringed Planet.
Cassini begins Rev99 on December 31 at its farthest distance from Saturn, called apoapse. At this point, Cassini is 1.18 million km (738,000 mi) from Saturn. Although Rev99 is a high-inclination orbit, Cassini will decrease its orbital inclination throughout 2009 using 13 Titan flybys before returning to the ring plane in October. In the meantime, the spacecraft will continue to use its high-inclination orbits to study the rings and the polar regions of Saturn and its satellites.
On the first day of Rev99, ISS will observe two of Saturn's moons, Dione and Titan. From a distance of 1.08 million km (668,000 mi), ISS will study the photometry of Dione's leading hemisphere. Titan's sub-Saturn hemisphere will be imaged from a distance of 2.24 million km (1.39 million mi).
For the first four days of 2009, ISS will focus on the atmosphere of Saturn. On January 1 and 2, ISS will take three two-frame, wide-angle camera mosaics covering the eastern half of Saturn as seen from Cassini. The third of these mosaics may include the shadow of Tethys as it crosses above the shadow of the rings. On January 2 and 3, ISS and the Visual and Infrared Spectrometer (VIMS) will monitor cloud dynamics in Saturn's north polar region. In addition to these Saturn observations, ISS will turn back to Titan on January 2 to look for clouds across the northern part of its leading hemisphere.
On January 4, Cassini reaches periapse, its closest point to Saturn on Rev99. At that point, Cassini will be 548,000 km (341,000 mi) from Saturn's center. Before periapse, ISS and the Ultraviolet Imaging Spectrometer (UVIS) will look at aurorae near Saturn's north pole. ISS also will collect photometric data from a crescent Tethys. The next day, ISS and VIMS will make two more cloud dynamics observations, this time covering the south polar region.
For the last four days of Rev99, Cassini will again focus on Saturn, with a few rings and satellite observations mixed in. From January 6 to 9, ISS each day will make a two-frame, wide-angle camera mosaic covering the eastern half of Saturn. On January 6, ISS will record a high-phase observation of Titan from a distance of 1.22 million km (756,000 mi). The filters used during this observation will allow scientists to search for clouds across Titan's south polar region and to study the moon's upper haze layers. On January 8, ISS will exploit the first of many opportunities to examine the shadow of one of Saturn's moons displayed across the ring system. In this case, the shadow of Epimetheus will cross the rings. Also on January 8, ISS will look at several of Saturn's small satellites, including Pandora, Atlas, Suttungr, Janus, and Prometheus.
Cassini reaches apoapse on January 9, beginning Rev100.
Image products created in Celestia. All dates in Coordinated Universal Time (UTC).