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Cassini continues its exploration of the Saturn system with the 13-day Rev180, which begins on January 25 at its farthest distance from the planet. This is also called the orbit's apoapse. At this point, Cassini is 1.66 million kilometers (1.03 million miles) from Saturn's cloud tops. Rev 180 occurs eight 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. Thirty-one ISS observations are planned for Rev 180 with the majority focused on Saturn's atmosphere and rings.
On January 26, ISS begins its observations for Rev 180 a day after apoapse with 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. Seven more are planned between January 28 and 30, while another eight will be taken February 3 and 7, after periapse. Later on January 26, ISS will ride along with a Visual and Infrared Mapping Spectrometer (VIMS) stellar occultation observation by the ring system of the red giant star R Lyrae (one of the brightest stars in the night sky, in the near-infrared). On January 27, 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. On January 28 and 29, ISS will acquire a series of images of Saturn 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 January 30, ISS will ride along with another VIMS stellar occultation by the ring system of the Mira-like, red giant star R Cassiopeiae.
On February 1 at 05:32 UTC, Cassini will reach periapse for Rev 180 at an altitude of 388,490 kilometers (241,400 miles) from Saturn. Late on January 31, ISS will acquire a series of images of Saturn's A ring, surveying propellers in the ring. Propellers are small voids in Saturn's rings created by the gravitational interaction between large ring particles and the surrounding ring. Afterwards, on February 1, ISS will acquire high-resolution images of the F ring. On February 2, ISS will again ride along with a VIMS stellar occultation by the ring system of a Mira-like, red giant star, this time taking a look at W Hydrae. Later that day, ISS will acquire a movie of the Cassini Division and the outer edge of the B ring.
On February 3 and 4, ISS will acquire low-phase movies of Saturn's inner most ring, the faint D ring. These observations will focus on the brighter ringlets within the D ring. Also on February 3, ISS will acquire a 20-hour light curve observation of the small, outer moon, Erriapus. Light curve observations are used to determine the length of the moon's day. On February 4, 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. Another astrometric observation will be taken on February 5. Later that day, ISS will observe Aegaeon and the arc of dust that surrounds it in the G ring for twenty-one hours.
On February 7, Cassini will reach apoapse of this orbit, bringing it to a close and starting Rev181.
Image products created in Celestia. All dates in Coordinated Universal Time (UTC).