[For trouble viewing the images/movies on this page, go here]
Cassini continues its exploration of the Saturn system with the 13-day Rev177, which begins on December 16 at its farthest distance from the planet. This is also called the orbit's apoapse. At this point, Cassini is 1.65 million kilometers (1.03 million miles) from Saturn's cloud tops. Rev 177 occurs seven months into the first inclined phase of the Cassini Solstice Mission, a phase which lasts until March 2015. The inclined phase will allow for polar views of Saturn and Titan as well as better vistas of Saturn's rings than those Cassini had while in the earlier, equatorial phase of the Solstice Mission. Twenty-four ISS observations are planned for Rev 177, evenly mixed between observations of Saturn's atmosphere, rings, and moons. Rev177 also includes a close, non-targeted flyby of Rhea, the planet's second largest moon.
ISS begins its observations for Rev 177 the day after apoapse with an observation of a half-phase Titan from a distance of 1.10 million kilometers (0.68 million miles). This observation is designed to look for clouds in the moon's atmosphere as part of the "Titan Monitoring Campaign" (TMC). This observation is designed to monitor clouds over the moon's southern and sub-Saturn hemispheres. ISS also will be taking shorter-wavelength images to study changes in Titan's upper haze layers. On December 18, ISS will acquire an astrometric observation of Saturn's small, inner moons. Astrometric observations are used to improve our understanding of the orbits of these small satellites, which can be influenced by Saturn's larger icy moons. Two more astrometric observations will be taken on December 25 and 27. Also on December 18, ISS will ride along with an Ultraviolet Imaging Spectrometer (UVIS) observation of the bright star Vega as the moon Rhea passes in front of it. Afterward, ISS will acquire a movie of the F ring, observing its various channels and streamers created by the interaction between the ring material and the nearby moon Prometheus. A similar movie will be takena week later on December 25. On December 19, ISS will acquire a series of images of Saturn's rings using the WAC. These images will be tracking spokes -- a ring phenomenon Cassini has monitored throughout the mission -- over the B ring. With Cassini over the unlit side of the rings and with Saturn at a high phase angle, the spokes, if visible, will be brighter than the dark B ring.
On December 23 at 08:30 UTC, Cassini will reach periapse for Rev 177 at an altitude of 387,610 kilometers (240,850 miles) from Saturn. The day before, December 22, ISS will acquire a six-hour light curve observation of the small, distant moon Surtur. The spacecraft will take nearly 40 images over those ten hours in order to improve the estimate for its rotation period and to determine the position of its north pole. Also on December 22, at 23:06 UTC, Cassini will pass by Rhea at a distance of 23,650 kilometers (14,695 miles). ISS will acquire three mosaics of the icy satellite covering its trailing hemisphere and north polar region. The 26-image mosaic covering portions of the trailing hemisphere will have a peak resolution of 140 meters (460 feet) per pixel. A seven-image mosaic covering the north polar region will have a resolution of 240 meters (790 feet) per pixel. Afterward, early on December 23, ISS will monitor the south polar plume of Enceladus from a distance of 700,000 kilometers (435,000 miles). Finally, ISS will image Dione's northern hemisphere at a distance of 248,000 kilometers (154,000 miles).
On December 24, ISS will acquire a quick observation of Saturn using the wide-angle camera (WAC). These observations are part of a series of "Storm Watch" observation sequences designed to take advantage of short, two-minute segments when the spacecraft turns the optical remote sensing (ORS) instruments back to Saturn as a waypoint between other experiments' observations. These sequences include blue, clear, two methane band, and one full-frame, continuum band filter images. Six additional sequences will be taken between December 25 and 27. Also on December 24, ISS will acquire another light curve observation of Surtur, this one lasting fourteen hours. On December 25 and 27, ISS will search for clouds on Titan as part of its TMC campaign. These two observations will focus on the Fensal-Aztlan region of the moon and will be taken from a distance of 2.12 million kilometers (1.32 million miles). On December 26, ISS will then look at the faint inner D ring for a ten-hour movie observation. Finally, on December 27, ISS will observe Anthe and the arc of dust that surrounds it for ten hours
On December 29, Cassini will reach apoapse on this orbit, bringing it to a close and starting Rev178.
Image products created in Celestia. All dates in Coordinated Universal Time (UTC).