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Cassiniís journey at Saturn continues with its 41st orbit of the ringed planet, as Cassini observes Titanís trailing hemisphere and Saturnís atmosphere and ring system.
Cassini begins its 41st orbit, Rev40, on February 27 at its farthest distance from Saturn, called apoapse. (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.)
The first week of Rev41 is relatively quiet, compared to the previous orbit. Cassiniís 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 Saturnís shadow as it is cast on the ring plane.
Activity for the Cassini camera doesnít ramp up until March 6, when Cassini will observe the limb of Saturn over the course of single Saturn day (about 10-and-three-quarter hours). These observations, taken in multiple filters for probing a variety of depths in the atmosphere, are designed to understand how the vertical structure of Saturnís upper atmosphere changes at night when compared to similar observations taken over the day side of Saturn. The observation is designed to use the rings as a background light source to probe the atmosphere. Observations to probe the atmosphere at its limb have also been conducted with Cassiniís Ultraviolet Imaging Spectrometer, whereby a bright star is observed as it is occulted by the planet.
Cassini encounters Titan for the 27th time on March 10, with a closest approach distance of only 980 km (608 mi). Like T25 during the previous orbit, this flyby (known as T26) will allow for imaging of the northern portion of Titanís trailing hemisphere following closest approach. The Cassini cameras will take three mosaics of this region. The mosaic design for the highest resolution mosaic can be seen here. This mosaic (and a lower resolution context mosaic) focus on a region centered at 45ļ North Latitude, 230ļ West Longitude, north of the dark region named Belet. Prior to T25, the region had not been observed at image scales better than 35 km (21 mi) per pixel, but these observations will allow features as small as 2 km (1.2 mi) across to be resolved. The T26 observations will allow for a follow-up on discoveries made in T25 images and examination of some of the terrain observed by the RADAR instrument during T21 (December 12, 2006).
The last 5 days of Rev40 are once again relatively quiet. Several observations are planned to image many of Saturnís small satellites to refine the orbits of these little worlds. On March 12, Cassini will observe Titan from a distance of 1.34 million kilometers (830,000 miles), allowing for images of Titanís north polar region (on the anti-Saturn side) at image scales better than 8 kilometers (5 miles) per pixel.
Cassini begins orbit 42, Rev41, on March 15, during which Cassini take additional observations of Saturnís ring system and encounter Titan for T27.