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Cassini's journey at Saturn continues with its 42nd orbit of the ringed planet, as Cassini observes Titan's trailing hemisphere and Saturn's atmosphere and ring system.
Cassini begins Rev41, on March 15 at its farthest distance from Saturn, called apoapsis. (Remember that Rev01 and Rev02 where replaced by three orbits, RevA through RevC, earlier in the mission. Hence, the numbering scheme for orbits is offset.)
As during the previous orbit, the first week of Rev41 is relatively quiet. And just like the previous orbit, Cassini's focus will be on the ring system, observing the rings at high phase angles several times during the first week. These observations include a set dedicated to observing the boundary of Saturn's shadow as it is cast on the ring plane.
On March 21, Cassini's cameras will capture a mosaic of the entire ring system. At this point in the orbit, Saturn is nearly between Cassini and the Sun, leaving only a thin Saturn crescent visible to the spacecraft. This is what scientists call a 'high phase' geometry. Observations of the rings in this geometry will help in understanding the photometric properties of the ring system, which in turn aids in determining the variations in particle sizes and the densities of particle concentrations across the rings.
Cassini encounters Titan for the 28th time on March 26, with a closest approach distance of only 1,010 km (627 mi). Like T25 and T26 during the previous couple of orbits, this flyby (known as T27) will allow for imaging of the northern portion of Titan's trailing hemisphere following closest approach. The Cassini cameras will take two mosaics of this region. This mosaic (and a lower resolution context mosaic) focuses on a region centered at 45° North Latitude, 240° West Longitude, north of the dark region named Belet. The T27 observations will allow for a follow-up on discoveries made in T25 and T26 images, such as the ISS discovery of a Caspian-Sea-sized body of (presumably liquid hydrocarbons) and an examination of some of the terrain observed by the RADAR instrument during T21 (December 12, 2006). The discovery of northern mid-latitude clouds last month suggests that observations such as these may also allow for cloud tracking. During closest approach, the Cassini bistatic experiment will use the high-gain antenna to search for specular reflections on Titan's surface and to study the electrical properties of the surface. One of the regions that the bistatic experiment will probe is in the south polar region, just east of the large dark feature named Ontario Lacus, seen in ISS images and the first lake-like feature discovered by Cassini. The bistatic results may provide additional evidence that the dark features seen in the south polar region, which imaging team members have been presuming since June 2005 constitute a 'lake district' at the south pole, are filled with liquid, like similar features observed at the north pole.
The last 5 days of Rev41 are once again relatively quiet. Several observations are planned to image many of Saturn's small satellites to refine the orbits of these little worlds. On March 29, Cassini will observe Titan from a distance of 1.45 million kilometers (830,000 miles), allowing for images of Titan's north polar region (on the anti-Saturn side) at image scales better than 8.7 kilometers (5.4 miles) per pixel. This observation was designed to study photometry of Titan's atmosphere and surface, but this observation will also allow for continued monitoring of the large, Caspian Sea-sized dark region discovered in late February.
Cassini begins orbit 43, Rev42, on March 31, during which Cassini take additional observations of Saturn's ring system as well as Saturn's moons Dione, Hyperion, Titan (during the T28 flyby), and Iapetus.