[For trouble viewing the images/movies on this page, go here]
Cassini continues its extended tour of Saturn on June 2 with Rev112, the spacecraft's 113th orbit around the Ringed Planet. Cassini begins Rev112 early on June 2 at its farthest distance from Saturn, called apoapse. At this point, Cassini is 1.65 million kilometers (1.02 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.
Cassini starts its observations for Rev112 shortly after apoapse. During the first two days of Rev112, Cassini ISS will a calibration observation using the apparent double star, 77/78 Tauri in the Hyades open star cluster. On June 3, ISS will take 263 images of the outer satellite Kiviuq over a period of more than nine hours. This observation is designed to measure the light curve of this small satellite, which can be used to derive the rotational period of the small moon. A shorter, follow-up observation is planned for June 15 to separate possible models for Kiviuq's rotation with respect to its light curve (double peak versus single peak).
Cassini encounters Titan on June 6 at 20:00 UTC for the 57h time and the first encounter this month. This flyby is also the fifth 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. This flyby, known as T56, will allow for imaging of the southern trailing hemisphere of Titan outbound to the encounter, similar to the area observed during the previous four encounters in this series. On approach to Titan, the Composite Infrared Spectrometer (CIRS), ISS, Visual and Infrared Mapping Spectrometer (VIMS), and RADAR teams will be controlling spacecraft pointing, or will be considered "prime." CIRS will focus on measuring Titan's atmospheric composition by mapping the visible disk of Titan at far-infrared wavelengths. VIMS and ISS will use their time to observe Titan's north polar region, looking for cloud bands in this region. Cloud streaks have been observed at high-northern latitudes several times over the last few months. RADAR begins observing Titan five hours before closest approach, starting with a passive radiometry scan of the entire visible disk which will allow the team to measure the dielectric constant and radiometric temperature of various terrains on Titan's surface, including the north polar lakes region.
During closest approach on T56, RADAR will be prime. On approach after its radiometry scan, RADAR will perform several scans using its scatterometry mode, acquiring regional backscatter images of Titan's surface, particularly over the northern leading hemisphere. RADAR will also take a distant HiSAR observation of northern Xanadu as well as an altimetry swath in the same region covered in 2006: the end of the T16 Synthetic Aperture RADAR (SAR) swath taken in July 2006. In the 18 minutes surrounding closest approach, RADAR will acquire a SAR swath running northeast to southwest from north of Xanadu (around 25 degrees north, 130 degrees west), across Shangri-la, and ending in the south polar region near 66 degrees south, 300 degrees west. The features that RADAR will observe in this swath include eastern Crete Facula, an area of bright terrain in northeast Shangri-la; Kerguelen Facula; two pairs of dark, crisscrossing lineaments named Bacab Virgae and Perkunas Virgae; and an east-west dark lineament in Titan's southern mid-latitude terrain named Hobal Virga. This swath parallels to the east and south the swath acquired during the previous encounter, T55. Following this SAR swath (and Titan closest approach), RADAR will acquire an altimetry swath to the east of the end of the SAR data.
Following close approach, the Ultraviolet Imaging Spectrometer (UVIS), VIMS, and CIRS will trade off being prime. UVIS will observe a stellar occultation of Titan's atmosphere, using the B-type star Eta Ursa Majoris at the end of the Big Dipper's handle. UVIS also will acquire a north-south scan across the visible disk of Titan, measuring latitudinal variations in the far and extreme ultraviolet spectrum of Titan's atmosphere. During CIRS's observation time, the infrared spectrometer will measure Titan's atmospheric composition by mapping the visible disk of Titan in the far-infrared. Finally, VIMS and ISS will acquire a global mapping observation.
Following the T56 flyby, Cassini imaging will be focused on Saturn's ring and satellite systems. On June 8, ISS will take a look at Saturn's rings as the shadows of Daphnis, Epimetheus, and Enceladus cross the rings. Cassini will observe Titan's sub-Saturn hemisphere on June 9 from a distance of 1.15 million kilometers (711,000 miles). Shortly before periapse, Cassini ISS also will take a 1-hour long, time-lapse movie of the F ring.
On June 9, Cassini reaches periapse, its closest point to Saturn on Rev112. At this point, Cassini will be 514,280 kilometers (319,560 miles) from Saturn's cloud tops, just outside the orbit of Rhea. During periapse, ISS will observe the shadows of Janus and Tethys as they cross Saturn's ring system and, in the case of Tethys, the planet's atmosphere. ISS also will take another time-lapse movie of the F ring, this time lasting nearly three hours and containing 100 images.
On June 10, Cassini will take a third movie of the F ring as the spacecraft approaches the ring plane from below. The observation is designed to study the evolution of channels and streamers created by Prometheus when it is at apoapse in the narrow ring. These effects are predicted to become more pronounced as Prometheus dives deeper into the F ring as the apoapse of Prometheus's orbit and periapse of the F ring become aligned, which will occur in December. On June 12, ISS will acquire a 9-frame, wide-angle camera mosaic of the unlit face of the ring system. This observation and others like it over the last few months can be used to measure how the brightness of various rings change as the sun angle decreases as equinox approaches. ISS also will take an astrometric observation of several of Saturn's small satellites including Polydeuces, Pallene, Anthe, and Aegaeon (the newly-discovered, G ring arc satellite). Astrometric observations are used to help provide better orbital calculations for some of these small rocks which can be affected by gravitational interactions with the larger icy moons.
On June 13, ISS will observe Titan's northern leading hemisphere from a distance of 2.1 million kilometers (1.3 million miles). The main goal of the observation is to look for clouds in the north polar region, as has been observed during the last few orbits. On June 14, ISS will observe the shadow of Epimetheus fall across the Saturnian ring system. ISS will take an astrometric observation of several of Saturn's small satellites, observing Janus, Anthe, Prometheus, Pandora, and Pan. Finally, ISS and UVIS will perform a calibration sequence by observing the B-type star Spica, the brightest star in the constellation Virgo. On June 15, in addition to the follow-up Kiviuq observation mentioned earlier, ISS also will acquire an astrometric observation of Pandora, Pan, Pallene, Epimetheus, and Prometheus, as well as an observation of the shadows of Tethys, Mimas, and Epimetheus on Saturn's rings.
During the last two days of observations for Rev112, June 16 and 17, Cassini ISS will acquire another astrometric observation of Saturn's small satellites, this time taking a look at Epimetheus, Pan, Methone, and Prometheus. ISS also will image HD 20630, a 4.83-magnitude, G-type star in the constellation Eridanus. This observation will be used to update the imaging team's calibration files.
Cassini reaches apoapse on June 17, bringing Rev112 to an end and starting Rev113. Rev113 will include Cassini's 58th flyby of Titan, T57.
Image products created in Celestia. All dates in Coordinated Universal Time (UTC).