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Cassini continues its exploration of the Saturn system with the 21-day Rev 195, which begins on July 15 at its farthest distance from the planet. This is also called the orbit's apoapse. At this point, Cassini is 1.46 million kilometers (0.90 million miles) from Saturn's cloud tops. Rev 195 occurs during the first inclined phase, which lasts until March 2015, of the Cassini Solstice Mission. 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-six ISS observations are planned for Rev 195 with many focused on Titan, during a targeted flyby of that moon, and Saturn's atmosphere.
On July 15, five minutes after apoapse, ISS will ride along with an Ultraviolet Imaging Spectrometer (UVIS) observation of Saturn's atmosphere. UVIS will perform a limb-to-limb scan across Saturn using its extreme- and far-ultraviolet channels. ISS will acquire a set of narrow-angle (NAC) and wide-angle (WAC) photometry images of the planet during the scan. Similar scans and ride-along observations will be performed once each day between July 16 and July 18. On July 17, ISS will look for clouds across Titan's southern sub-Saturn hemisphere from a distance of 1.31 million kilometers (0.81 million miles).
On July 19, ISS will ride-along with a Visual and Infrared Mapping Spectrometer (VIMS) mosaic of Saturn and its ring system while Cassini is in the planet's shadow. With the sun blocked by the planet, Cassini can acquire images of Saturn and the rings at a higher phase angle than it normally would be allowed to. This observation, put into the sequence by imaging team leader Carolyn Porco for a special public global outreach event 'The Day The Earth Smiled', will include NAC and WAC images of Earth. The narrow angle images will have high enough resolution to show the Earth and the Moon as distinct points of light. Earth will be 9.666 astronomical units (898.5 million miles) away when Cassini images the planet. For more information about the Earth imaging event, visit the event page.
On July 23 at 05:40 UTC, Cassini will reach periapse for Rev 195 at an altitude of 867,010 kilometers (538,740 miles) from Saturn. On July 20, ISS will ride-along with UVIS as it performs another scan across Saturn, similar to observations taken over the last few days. While the scan on July 20 will last just shy of two hours, UVIS and ISS will perform similar observations each day between July 21 and July 24 that will typically last around 12 hours. On July 21, ISS will ride along with an UVIS observation of Saturn's south polar aurora. In addition to making a movie of the planet's aurorae, the images will be used to independently measure the rotation period of Saturn's magnetic field. A few hours before periapse, ISS will ride along with VIMS to acquire a mosaic of Saturn's north polar region using the WAC. Spring has progressed far enough that the entirety of the hexagonal jet stream that lies near 77 degrees North latitude will be in sunlight. ISS will be imaging the hexagon with a two-by-two mosaic rather than centering the field-of-view on the north pole. Late on June 23, ISS will ride-along with VIMS as it maps the clouds across Saturn's northern hemisphere.
Three days after periapse, Cassini encounters Titan on July 26 at 11:56 UTC for the 94th time. This is the fifth Titan flyby planned for 2013, with the next encounter scheduled for September 12. T93 has a close-approach altitude of 1,400 kilometers (870 miles). This flyby will allow for imaging of the north polar region inbound to the encounter and the southern anti-Saturn hemisphere of Titan on the outbound leg. Starting off the encounter, ISS will ride-along with the Composite Infrared Spectrometer (CIRS) as it stares at Titan in order to acquire mid-infrared spectral and temperature information about Titan's atmosphere. Afterward, ISS will acquire a seven-frame mosaic of the north polar and northern leading hemisphere regions of Titan. This mosaic will provide more information of the distribution of lakes in the north polar region, fill-in the largest gap in ISS's map of Titan, and provide ISS's highest resolution observation of the impact basin Menrva to date. Afterward, ISS will ride-along with two more CIRS and UVIS scans of Titan's northern hemisphere. As Cassini approaches Titan, ISS will acquire two, two-frame mosaics of Titan. The first pair of images will cover Ganesa Macula and the terrain to its northeast. The second pair of images will cover the lakes Feia Lacus and Abaya Lacus. These lakes were previously observed by RADAR during the T18 and T83 flybys.
VIMS will be the prime instrument at closest approach. During its two hours of observing time, VIMS will acquire several observations of Titan's surface. During the approach to Titan, VIMS will focus on the north pole and Punga Mare followed by imaging of eastern Ligeia Mare and the lakes and playas to the south and east of Ligeia, like Uvs Lacus. During closest approach, VIMS will acquire a noodle image running south from Ligeia Mare, down Titan's northern mid-latitudes, ending up across the equatorial Belet dune field. VIMS will then acquire a mosaic across southern Belet, covering a series of faculae (bright regions within Titan's dune fields). This mosaic includes areas affected by the Arrow Storm in September and October 2010, though from previous ISS and VIMS imaging, the region has returned to the way it looked before the storm.
After VIMS's close-approach observations, ISS will acquire a pair of mosaics covering a part of Titan's southern mid-latitude "blandlands". The first mosaic includes six-frames and will be centered on 53 degrees South latitude, 237 degrees West longitude. The second mosaic contains seven frames and is largely a continuation of the previous mosaic, covering the terrain around the region covered by the previous mosaic. Images in these two observations will be taken from distances ranging from 23,400 to 75,000 kilometers (14,540 to 46,600 miles) away. Five hours later (after a CIRS limb scan), ISS will ride-along during a VIMS observation in order to track any clouds that might be visible across Titan's southern, anti-Saturn hemisphere. On July 27, ISS will acquire three Titan cloud tracking observations that will cover its southern hemisphere.
On July 28, 29, 30, and August 4, ISS will ride along with UVIS while it performs extreme- and far-ultraviolet scans of Saturn. ISS will take WAC and NAC images of the planet's southern hemisphere. On July 30, ISS will take another look at Titan, looking for clouds across the moon's southern trailing hemisphere from a distance of 1.44 million kilometers (0.89 million miles). On July 31, ISS will acquire an observation of the small, outer satellite, Paaliaq. These images will be used to measure the rotation period of these small moons. Given its small size and great distance from Saturn, it doesn't rotate synchronously like Saturn's closer and larger icy moons. Paaliaq is 22 kilometers (14 miles) across and will be 10.7 million kilometers (6.64 million miles) away. Its rotational period had previously been found to be between 19 and 20.5 hours, but this observation should help to refine the estimate for the length of its day. On August 4, ISS will observe a crescent Titan from a distance of 1.97 million kilometers (1.23 million miles).
On August 5, Cassini will reach apoapse, bringing Rev 195 to a close and starting up the next orbit, Rev 196.
Image products created in Celestia. All dates in Coordinated Universal Time (UTC).