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Cassini’s journey at Saturn continues with Rev 58, its 59th orbit of the ringed planet. Cassini’s slate of observations this orbit includes a distant encounter with Dione and numerous observations of Saturn’s rings and small moons. Cassini begins Rev58 on February 2 at its farthest distance from Saturn, called apoapsis. At this point, Cassini is 1.81 million km (1.13 million mi) from Saturn. The first four days of Rev58 contain several observations of Saturn’s small satellites and ring system. On February 3, Cassini performs several small satellite observations – designed to study the orbits of these objects and how they might evolve over short time periods due to perturbations from the other moons in the system. On February 4, Cassini performs similar observations of Helene, one of two small satellites that shares Dione’s orbit. Here, Cassini will track Helene for 13 hours. Also on February 4, Cassini will observe the B ring, looking for variations in its features in the longitudinal (or around-Saturn) direction. Cassini will take a similar look on February 5, this time riding along with a CIRS observation. Also, on February 3, ISS will perform a calibration test. Cassini reaches periapse, the closest point in its orbit, on February 8 when the spacecraft is 199,000 km (124,000 mi) above Saturn’s cloud tops. On February 8 and 9, Cassini will perform a couple of imaging sequences of Dione. The first is a distant look at Dione’s north polar region. The second is a close-up look at Dione’s sub-Saturn hemisphere, similar to an area examined during a very close non-targeted encounter in August 2007. Images from these two encounters could be combined to look at the features of this hemisphere in stereo.
The other observations acquired during the periapse period are of Saturn’s ring system. On February 7, Cassini will observe the “1.470 Rs ringlet,” an eccentric ring within a gap in the outer C ring. On February 10, ISS and VIMS will observe the Cassini Division and the Huygens Gap in the outer B ring as Cassini crosses the ring plane, allowing for a study of the photometry of that region of the ring system and a chance to search for small satellites. Finally, on February 11, Cassini will look for spokes on the unlit side of the rings.
Cassini finishes Rev58 with several small satellite orbital determination sequences.
Cassini begins the following orbit, number 60 (“Rev59”), on February 14. Rev59 includes a targeted flyby of Titan.