[For trouble viewing the images/movies on this page, go here]
Cassini continues its extended tour of Saturn on with Rev114, the spacecraft's 115th orbit around the Ringed Planet. Cassini begins Rev114 on July 3 at its farthest distance from Saturn, called apoapse. At this point, Cassini is 1.95 million kilometers (1.21 million miles) from Saturn's cloud tops. The spacecraft remains in a high-inclination orbit, providing an opportunity to study the rings and the polar regions of Saturn and its satellites. The Saturn system is nearing vernal equinox, which will occur on August 11 during Rev116.
Cassini ISS starts its observations for Rev114 two days after apoapse. On July 5, ISS will look at a crescent Titan from a distance of 1.34 million kilometers (835,000 miles). While this observation would not be good for observing surface features on Titan due to the high phase angle, these images would help in characterizing any changes in the haze layers in the moon's upper atmosphere as the result of the approaching equinox or Titan's position in Saturn's magnetosphere. On July 7, ISS will take a 16-frame, wide-angle-camera mosaic of the entire Saturn system out to the orbit of Enceladus. This mosaic will include not only a crescent Saturn, but the faint, unlit side of the ring system and the icy satellites Mimas, Enceladus, and Tethys.
Cassini encounters Titan on July 8 at 17:28 UTC for the 59th time and the first encounter this month. This flyby is also the seventh in a series of 10 flybys between April and August 2009 that will be spaced 16 Earth days, or one Titan day, apart and occur as Cassini is inbound toward Saturn. The close approach distance is only 965 kilometers (600 miles), close to the lowest safe altitude for a Titan flyby during the extended mission. This flyby, known as T58, will allow for imaging of the southern trailing hemisphere of Titan outbound to the encounter, similar to the area observed during the previous five encounters in this series. On approach to Titan, the Ultraviolet Imaging Spectrometer (UVIS) and Visual/Infrared Mapping Spectrometer (VIMS) teams will be controlling spacecraft pointing, or be considered "prime." VIMS will observe the crescent of Titan, looking for clouds over the north polar region as well as looking Tui Regio on Titan's nightside. In the latter case, VIMS will be searching for thermal emission from this potentially cryovolcanic structure. UVIS will acquire two far- and extreme-ultraviolet spectroscopy scans of Titan at high phase angles, looking at the hydrocarbons in the north polar hood.
During closest approach on T58, the UVIS and RADAR will be prime. Between 30 and 90 minutes before closest approach, UVIS will observe a solar occultation of Titan's north polar atmosphere by tracking the Sun with UVIS solar occultation, high-speed photometer as the Sun passes behind Titan and its atmosphere. By measuring how ultraviolet sunlight is affected by its passage through Titan's atmosphere, the UVIS team can better understand the structure of Titan's upper haze layers and how these layers change over time. In the hour surrounding closest approach, RADAR will be prime, acquiring a Synthetic Aperture RADAR (SAR) swath running northeast to southwest from western Xanadu (around 0 degrees south, 140 degrees west), along the boundary between Xanadu and Shangri-la, across the mid-latitude terrain south of Shangri-la, dipping down to the south polar region as far south as 80 degrees south near 240 degrees west, and ending near 55 degrees south, 320 degrees west. The features that RADAR will observe in this swath include two pairs of dark, criss-crossing lineaments named Bacab Virgae and Perkunas Virgae; an east-west dark lineament in Titan's southern mid-latitude terrain named Hobal Virga; and Ontario Lacus, a large lake in Titan's south polar region first observed by ISS in June 2005. This swath parallels to the east and south the swath acquired during the previous encounter (T57). Following this SAR swath, UVIS will observe a stellar occultation of Eta Ursae Majoris by Titan. The occultation will allow UVIS to probe the haze layers over Titan's mid-southern latitudes.
Following close approach, the Composite Infrared Spectrometer (CIRS), VIMS, and ISS teams will trade off being prime. VIMS will acquire a medium-resolution, four-frame mosaic covering the southern mid-latitude terrain south of Senkyo, including a series of bright streaks that the VIMS teams have interpreted as possible mountain chains. ISS will acquire three mosaics of Titan's visible surface. The first, REGMAP001, is a nine-frame mosaic that will be acquired from a distance of 70,000 to 100,000 kilometers (43,000 to 62,000 miles). This high-resolution mosaic will cover similar terrain as the VIMS mosaic earlier, including portions of eastern Tsegihi. The second mosaic, GLOBMAP001, is a 29-frame mosaic that will be acquired from a distance of 100,000 to 175,000 kilometers (62,000 to 109,000 miles). The third mosaic, MONITORNA001, is a 14-frame mosaic that will be acquired from a distance of 240,000 to 280,000 kilometers (149,000 to 174,000 miles). MONITORNA001 will cover all the sunlit terrain seen in the figure at right.
On July 10, Cassini reaches periapse, its closest point to Saturn on Rev114. At this point, Cassini will be 259,000 kilometers (161,000 miles) from Saturn's cloud tops, between the orbits of Tethys and Dione. During periapse, ISS will acquire an azimuthal scan along the outer Cassini Division, looking for vertical structures along the edges of gaps in this part of the ring system. Several hours later, ISS will take several images from across the main ring system, looking for the shadows of vertical structures within the rings. On July 11 and 12, Cassini will take a look at the shadows of several of Saturn's moons on the ring system, including Epimetheus, Daphnis, and Janus. On July 12, Cassini ISS will observe Titan's northern sub-Saturn hemisphere from a distance of 2.21 million kilometers (1.37 million miles).
On July 13, ISS will take an astrometric observation of several of Saturn's small satellites including Pandora, Atlas, Janus, Methone, and Pallene. Astrometric observations are used to help provide better orbital calculations for some of these small rocks, which can be effected by gravitational interactions with the larger icy moons. ISS also will take an astrometric observation of some of the larger propellers, voids created by 100-meter-wide objects within the main ring system. Finally on July 13, ISS will acquire a time-lapse movie of the unlit side of the F ring.
On July 15, ISS will acquire another astrometric observation of some of the larger propellers in Saturn's A ring. ISS also will look at the shadows of several of Saturn's moon on the ring system, including Prometheus and Daphnis. On July 16, another astrometric observation will be acquired of several of Saturn's small satellites, including Pandora, Calypso, Helene, Epimetheus, and Pan.
Cassini reaches apoapse on July 18, bringing Rev114 to an end and starting Rev115. Finishing up Rev114, ISS will observe Saturn using the narrow- and wide-angle cameras and in numerous filters. The observation will provide a great look of Saturn's northern hemisphere and the thin shadow of the ring system as the planet approach equinox, by then only 3 weeks away.
Image products created in Celestia. All dates in Coordinated Universal Time (UTC).