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Cassini Significant Events 1/27/16 – 2/2/16

Cassini is currently orbiting Saturn with a period of 16 days in a plane inclined 17.5 degrees from the planet's equatorial plane. The most recent spacecraft tracking and telemetry data were obtained on Feb. 3 using one of the 34-meter diameter Deep Space Network stations in Australia. The spacecraft continues to be in an excellent state of health with all of its subsystems operating normally except for the instrument issues described at http://saturn.jpl.nasa.gov/news/significantevents/anomalies .

This week's highlight was an encounter with Saturn's hazy atmosphere-enshrouded moon Titan. The T-116 flyby provided another close look at this enigmatic world, as well as a gravity assist to further increase the inclination of Cassini's orbit about Saturn. Each future Titan encounter -- there are 10 more targeted flybys left in the mission -- will be affecting Cassini's inclination until it reaches 63.7 degrees for the F-ring orbits before leveling off to 62.4 degrees for its final, daring, Grand Finale next year.

Wednesday, Jan. 27 (DOY 027)

Cassini's Composite Infrared Spectrometer (CIRS) finished up an observation of Saturn’s atmosphere, measuring temperatures in the upper troposphere and tropopause. Next, the Imaging Science Subsystem (ISS) made a two-minute storm-watch observation on Saturn, before Cassini's Navigation team took control of ISS. Their 90-minute observation made images of Saturn's moon Dione against the background stars, for optical navigation purposes. Finally, the Ultraviolet Imaging Spectrograph (UVIS) spent 3.8 hours watching Saturn’s auroral oval.

Thursday, Jan. 28 (DOY 028)

ISS, CIRS, and the Visible and Infrared Mapping Spectrometer (VIMS) controlled spacecraft pointing to observe Saturn's largest moon Titan, as part of the Titan meteorological campaign. This 90-minute observation would be repeated on Friday and again on Saturday. Today's was followed by an ISS-led observation of the Cassini Division, which is the wide gap between Saturn's A ring and B ring. CIRS and VIMS participated. Over the course of nearly 12 hours, ISS recorded images to form a movie that will allow scientists to study, among other things, the kinematics of the many thin ringlets that populate this region.

Friday, Jan. 29 (DOY 029)

ISS acquired images for 90 minutes of several known propellers in Saturn's rings ( http://go.nasa.gov/17oqTWF ), features within the rings that are created by bodies significantly larger than typical ring particles, but too small to clear their own gaps and become moons in their own right. Next, the Cosmic Dust Analyzer (CDA) made a 4.5-hour observation of dust particles that are moving retrograde relative to the majority of the objects orbiting Saturn. CIRS then trained on the outer part of the C ring for six hours to obtain spectra at moderate resolution in the far infrared, looking for details of the ring particles' composition.

When Cassini turned its high-gain antenna to Earth following the CIRS observation, realtime commands arrived and controlled the spacecraft as it performed Orbit Trim Maneuver (OTM)-439. The flight team had decided to use the backup opportunity to do this OTM, one day later than the prime opportunity. Among other considerations, doing this saved a small amount of propellant. The 10-second firing of Cassini's small rocket thrusters provided a change in velocity of 16 millimeters per second, making a fine adjustment in targeting for the Feb. 1 Titan encounter T-116.

Saturday, Jan. 30 (DOY 030)

While the spacecraft passed periapsis in its Saturn orbit #231, it was also passing through Saturn's diffuse E ring, which originates from icy plumes issuing from the small moon Enceladus. CDA spent two hours characterizing the dust population in that region. ISS then turned towards Saturn's small satellite Anthe, which it observed for 1.7 hours while VIMS rode along. This object, about two kilometers in diameter, orbits within the E ring interior to the orbit of Enceladus. It was named after a figure in Greek mythology. Today's extensive color imaging will help determine this object's composition.

When this observation was complete, VIMS trained on the star Omicron Ceti, which passed behind Saturn's rings by virtue of Cassini's motion. This is one of the brightest stars in our sky at near-infrared wavelengths, and VIMS observed it during an ingress and egress ring occultation. The rings' opening angle for this star was only 3.5 degrees, creating long slant paths through the rings. As a consequence, both occultations should provide extremely good data on the optical depth profiles of the most transparent ring regions, including tenuous ringlets in several gaps.

ISS next turned to observe Saturn's innermost ring, the D ring, at a phase angle of around 160 degrees, a backlit geometry that enhanced the ring particles' visibility. Finally, UVIS observed for 5.25 hours while the bright blue-white star Zeta Orionis was occulted by Saturn's rings. CIRS rode along. Zeta Orionis is also known as Alnitak, the easternmost star in Orion's belt. Just as with the preceding VIMS occultations, the shallow angle highlighted the more tenuous features in Saturn's rings.

Saturn is one of the planets visible before dawn these days, as today's NASA's Astronomy Picture of the Day nicely illustrates: http://apod.nasa.gov/apod/ap160130.html .

Sunday, Jan. 31 (DOY 031)

By mid-day today, all eyes had turned to Titan; all Cassini's telescopic "eyes," that is. The optical instruments ISS, VIMS, CIRS, and UVIS began 27 hours of constant examination of the planet-like moon as it loomed ever closer.

Monday, Feb. 1 (DOY 032)

Closest approach to Titan came early in the day, at an altitude of 1,400 km above the surface of the 5,151 km diameter moon. During the encounter, UVIS observed both solar and stellar occultations behind Titan's atmosphere. In addition to the extensive optical science observations, the Magnetospheric and Plasma Science (MAPS) instruments recorded data during the encounter, which occurred in the late midnight sector of Saturn’s magnetosphere; Cassini explored parts of Titan's magnetosphere, which is induced by Saturn's magnetism. Cassini also took a gravity-assist nudge from the massive moon during the encounter, changing the spacecraft's orbital inclination from 4.1 degrees to the planned 17.5 degrees, as measured from Saturn's equatorial plane.

Cassini scientists attended the Outer Planets Assessment Group (OPAG) today and Tuesday at the Southwest Research Institute in San Antonio, Texas. OPAG is NASA's community-based forum designed to provide science input for planning and prioritizing outer planet exploration activities for the next several decades.

The soft, bright-and-dark bands displayed by Saturn in this Cassini view spacecraft are the signature of methane in the planet's atmosphere. The image is here: /resources/16300 .

Tuesday, Feb. 2 (DOY 033)

Today, ISS and VIMS spent eight hours making a movie of Saturn's faint E ring and G ring.

A remarkable scientific study of spiral density waves in parts of Saturn's most opaque ring, the B ring, has yielded some surprising results about the amount of mass in the middle of that ring. These results are reported in a news feature linked here: http://saturn.jpl.nasa.gov/news/cassinifeatures/feature20160202 .

During the past week, the Deep Space Network communicated with and tracked Cassini on eight occasions, using DSN stations in California and Australia. A total of 8,697 individual commands were uplinked, and about 1,765 megabytes of telemetry data were downlinked and captured at rates as high as 124,426 bits per second.

This illustration shows Cassini's position early on Feb 2: http://go.nasa.gov/1QSI8Ty . The format shows Cassini's path over most of its current orbit up to today; looking down from the north, all depicted objects (except the background stars of course) revolve counter-clockwise, including Saturn along its orange-colored orbit of the Sun.