[For trouble viewing the images/movies on this page, go here]
Cassini continues its new tour of the Saturn system with the 21-day-long Rev142, the spacecraft's 143rd orbit around the Ringed Planet. Cassini begins Rev142 on December 10 at its farthest distance from Saturn, called apoapse. At this point, Cassini is 2.62 million kilometers (1.63 million miles) from Saturn's cloud tops. Cassini's orbit lays nearly exactly within Saturn's ring plane, and within the orbital plane of most its major satellites, affording an opportunity to encounter a few of its moons. During Rev142, Cassini will fly by several of Saturn's moons, including Enceladus, Dione, and Daphnis.
ISS has a single observation prior to the periapse period. With Cassini in a very low inclination orbit, the spacecraft is in a great position to image the vertical structure of Saturn's diffuse E ring. ISS will perform a nearly day-long observation of the ring at moderate phase angles on December 12.
On December 20 at 22:49 UTC, Cassini will reach the periapse of Rev142, its closest point to Saturn in the orbit. At periapse, the spacecraft will be 155,590 kilometers (96,679 miles) above Saturn's cloud tops. During this periapse passage, Cassini will perform a targeted encounter of the active icy satellite, Enceladus. But first, six hours before periapse, Cassini will pass by Dione at a distance of 100,120 kilometers (62,211 miles). ISS will have two observations in conjunction with this non-targeted encounter. First, ISS will ride along with an observation by the Visual and Infrared Mapping Spectrometer (VIMS) starting 12 hours before closest approach. These images will be taken while Dione appears as a very thin crescent, making this a great opportunity to search for possible icy plumes from the moon. The inner moon Prometheus will pass through the field-of-view a few times during the observation. ISS frames will be timed so that images will catch Dione crossing the bright limb of Saturn. Two hours before closest approach, ISS will take a two-frame mosaic of a crescent Dione that will cover portions of its wispy terrain.
Also during this run up to periapse, ISS will image Titan from a distance of 934,490 kilometers (580,665 miles). Imaging scientists will be looking for clouds across the sub-Saturn hemisphere of Titan, as well as additional surface changes that may have occurred as a result of the large "Arrow Storm" that was seen in late September.
After periapse, Cassini will perform a targeted encounter of Enceladus. This encounter is also known as E13 as it is the 13th targeted flyby of this moon. The flyby will take place on December 21 at 01:08 UTC. Inbound, ISS will image the jets coming off the south polar region, while the Composite Infrared Spectrometer (CIRS) performs several scans across Enceladus in order to obtain a nighttime temperature map, useful for measuring the thermal inertia of the moon's surface. At closest approach, Cassini will fly just 48 kilometers (30 miles) over terrain at 62 degrees north latitude, 234 degrees west longitude on Enceladus, crossing the dawn terminator as opposed to the dusk terminator as it did during the previous flyby in the last orbit. At closest approach, Cassini will measure the composition of icy particles and vapor in its vicinity using the Ion and Neutral Mass Spectrometer and Cosmic Dust Analyzer. No images are planned during closest approach. Afterward, ISS will acquire a 10-frame mosaic across the anti-Saturn hemisphere of Enceladus. Each frame will consist of clear-filter images as well as images using the UV3 and IR1 filters (one frame will use the GRN filter instead of UV3). An extra clear filter image will be taken 27 minutes after the last frame for stereo coverage. Later, a ride along observation with VIMS will have ISS run through a variety of color filters of a full-disk Enceladus.
Finishing up Rev142, ISS will acquire 314 images of distant Siarnaq, a 40-kilometer-wide (25-mile-wide) outer moon of Saturn. These images will be used to build up a light curve of the satellite, which is useful for measuring the length of its day and understanding how its brightness changes depending on lighting conditions. On December 23 and 24, Cassini will perform astrometric observations of Saturn's small, inner moons. During these two observations, ISS will observe Telesto, Polydeuces, Methone, Janus (twice), Helene, Pandora (twice), Pallene, Prometheus, and Anthe. At the end of both observations, ISS will clean up with WAC images of Saturn. Also on December 23 and 24, ISS will image a half-phase Titan at distances of 2.49 million kilometers (1.55 million miles) and 2.76 million kilometers (1.72 million miles), respectively. The camera will image the sub-Saturn and leading hemispheres of the satellite, allowing researchers to continue to study the recent weather changes that have been occurring across Titan's equatorial region, which have brought rain to select regions of previously dry terrain.
On December 31, Cassini will reach apoapse on this orbit, bringing it to a close and starting Rev143. Rev143 includes non-targeted encounters with Titan, Pandora, and Methone. Cassini will also perform a close, targeted flyby of Rhea on January 11.
Image products created in Celestia. Enceladus and Dione basemaps by Steve Albers. All dates in Coordinated Universal Time (UTC).