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Cassini Significant Events 12/28/16 – 1/03/17

Floating high above the hydrocarbon lakes, wispy clouds have finally started to return to Titan's northern latitudes.
Floating high above the hydrocarbon lakes, wispy clouds have finally started to return to Titan's northern latitudes. › Full image and caption

Cassini Significant Events 12/28/16 - 1/03/17

Cassini's science activities were nearly non-stop as usual this week, while the spacecraft completed one more orbit in the Ring Grazing phase. On approach to the fifth ring-plane crossing, Cassini rang in the New Year with some fascinating images of Saturn’s rings (

). Back on Earth, development activities appeared on the work schedule for the mission's final command sequence, S101, which will go on board the spacecraft in July.

Wednesday, Dec. 28 (DOY 363)

Cassini's Ultraviolet Imaging Spectrograph (UVIS) spent 13.3 hours today observing Saturn's thermosphere, which is the layer high above its visible atmosphere. This is the region of space that Cassini will be flying through later this year, and observations such as today's are essential for learning about the area's dust environment, and about its gaseous density, which will determine how low the spacecraft can go before Saturn's atmosphere would cause it to start tumbling.

Over the years, Cassini has produced some astounding images of subjects in the far-off Saturn system. The Science team offers the following images, and science stories, as the best from 2016:


Thursday, Dec. 29 (DOY 364)

The Imaging Science Subsystem (ISS) dictated the spacecraft's orientation for the entire day, tracking Saturn's irregular satellite Erriapus. Named for a giant in Gaulish mythology, Erriapus is only about 8 kilometers in diameter. It has a very dark surface, and its inclined orbit takes it as far as 25.6 million km from Saturn.

Halfway through ISS's allocated time today, Cassini coasted through apoapsis in its orbit of Saturn, marking the start of Orbit #255.

Friday, Dec. 30 (DOY 365)

ISS began a study of Saturn's largest moon Titan that would last nearly 26 hours. The Composite Infrared Spectrometer (CIRS) and the Visible and Infrared Mapping Spectrometer (VIMS) rode along. During this period, Cassini came within 680,000 km of the haze-enshrouded world.

Sunday, Jan. 1 (DOY 001)

Cassini kicked off its final year today while speeding towards Saturn's ring-plane. ISS made some very high-resolution observations of Saturn's main rings, using multiple filters; CIRS and VIMS rode along.

Next, VIMS tracked the red star Gamma Crucis for 3.4 hours, while Saturn's rings occulted its light, going from the F ring inward through the inner D ring; CIRS rode along. Finally, CIRS observed the sunlit side of the mid-A ring, looking for structures in its so-called halo region, which contain unusual photometric properties believed to be associated with strong resonances with the orbits of at least one of Saturn's moons.

Monday, Jan. 2 (DOY 002)

Cassini sped through periapsis in its week-long orbit of Saturn today, just two days before Earth passed its own periapsis point in our year-long orbit of the Sun. Right before Cassini's periapsis passage, all its instruments were involved in making observations during the spacecraft's fifth ring-plane crossing close to Saturn's F ring. This time, observations included a new active Radar-sensing activity targeting the rings. Fifteen such F-ring crossings remain before the mission's Proximal Orbits begin (


CIRS observed Saturn's small active moon Enceladus for 2.5 hours, to determine the temporal variability of Enceladus' thermal activity. All the other optical remote-sensing instruments, VIMS, ISS and UVIS, participated.

Next, ISS spent two hours imaging the known "propeller" features (

) found in the A ring; CIRS rode along. ISS and CIRS then observed the outer regions of the A ring, the F ring, and the region between them, to study the complex dynamics in the vicinity of Saturn's Roche zone. Finally, CIRS recorded the infrared spectra of particles in the Cassini Division between Saturn's A and B rings; VIMS rode along.

Clouds have been spotted in the north on Titan, as today's featured image shows:


Tuesday, Jan. 3 (DOY 003)

The Radio Science team used the Deep Space Network plus one of the European Space Agency's Deep Space antennas today, to carry out another occultation experiment at three distinct radio wavelengths. As Saturn and then Saturn's rings occulted the spacecraft, the variations seen in its continuous signals will allow scientists to make inferences about the nature of Saturn's atmosphere and ring system. Next, CIRS observed the unlit side of rings, measuring their composition and structure.

NASA's Astronomy Picture of the Day featured Cassini's recent, unique view of Saturn's small moon Pandora today:


The Deep Space Network communicated with and tracked Cassini on 10 occasions this week, using stations in Spain, California and Australia; an ESA station participated one time from Australia. A total of 25 individual commands were uplinked, and about 1,200 megabytes of telemetry data were downlinked and captured at rates as high as 99,541 bits per second. During a typical Radio Science (RS) occultation experiment such as this week's, Cassini's three continuous radio signals are sampled at high rates at the ground sites, where they are stored and later shipped to JPL. One such experiment generates on the order of 50,000 megabytes of RS data.

Wrap up:

Cassini is executing its set of F-ring-grazing orbits of Saturn, with a period of 7.2 days in a plane inclined 63.7 degrees from the planet's equatorial plane. The 20 orbits are nearly identical, with Cassini's nearest point at about 150,000 km, and furthest point at about 1.28 million km from Saturn. Speeds relative to Saturn at those points (periapsis and apoapsis), are close to 76,150 km per hour and 9,000 km/h respectively.

The most recent spacecraft tracking and telemetry data were obtained on Jan. 4, using one of the 34-meter diameter DSN stations in California. 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


Information on the present position and speed of the Cassini spacecraft may be found on the "Present Position" page at:



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This illustration depicts Cassini's path up to mid-day Jan. 3. The countdown clock in Mission Control shows 254 days until the end of the mission.