6 min read

Cassini Significant Events 6/14/17 – 6/20/17

NASA's Cassini spacecraft sees bright methane clouds drifting in the summer skies of Saturn's moon Titan, along with dark hydrocarbon lakes and seas clustered around the north pole. › Full image and caption
NASA's Cassini spacecraft sees bright methane clouds drifting in the summer skies of Saturn's moon Titan, along with dark hydrocarbon lakes and seas clustered around the north pole. › Full image and caption

Cassini Significant Events 6/14/17 - 6/20/17

While the Cassini Spacecraft made another 6.5-day circuit of Saturn this week, some members of the flight team undertook far-ranging travels on Earth. Scientists on the Composite Infrared Spectrometer (CIRS) team met for three days in Oxford, England. Numerous Cassini scientists participated in the Magnetospheres of the Outer Planets (MOP) meeting in Uppsala, Sweden. While still in Europe following last week's Project Science Group meeting, the Cassini Program Manager and a few others visited and spoke with personnel at the Deep Space Network's Deep Space Communications Complex in Madrid, Spain, to express thanks for their support for Cassini over the years. Before leaving the Spanish capital, they also gave a well-received public talk, hosted by the Madrid Planetarium.

Wednesday, June 14 (DOY 165)

Cassini was gradually gathering speed with respect to Saturn today, while it continued its dive from the previous day's apoapsis. From this perspective, the optical instruments' target today was Saturn; the Ultraviolet Imaging Spectrograph (UVIS) spent 18.7 hours leading an observation of the gas giant's northern sunlit crescent at extreme- and far-ultraviolet wavelengths. All the other optical instruments rode along: CIRS, the Imaging Science Subsystem (ISS), and the Visible and Infrared Mapping Spectrometer (VIMS). Today's viewing geometry is illustrated here.

This recently taken image of Saturn's largest moon Titan shows that its weather has been changing as northern summer sets in: /resources/17694.

Thursday, June 15 (DOY 166)

VIMS mapped Saturn's northern hemisphere for 3.5 hours today, with CIRS riding along. The infrared views help measure winds in Saturn's north polar vortex and hexagon with unprecedented precision, at depths nearly two times the barometric pressure at the Earth's surface.

When this was completed, ISS led CIRS and VIMS in a 90-minute Titan weather monitoring observation. This was repeated on Saturday, though without VIMS, and on Tuesday, again with CIRS and VIMS.

Saturn is at opposition today; it rises into Earth's sky at sunset, offering fine viewing opportunities all night in most any kind of telescope.

Friday, June 16 (DOY 167)

The spacecraft began its final approach for orbit #279 today, coming in for its ninth proximal plunge. Turning back to view Saturn again, UVIS made auroral observations for 10.5 hours, consisting of repeated slews across the planet's bright northern auroral oval. CIRS rode along, while the Magnetospheric and Plasma Science (MAPS) instruments made their in-situ measurements along the same magnetic field lines that intersect the auroral zone.

Ring-plane crossing came late in the day, followed by periapsis passage just three minutes later. During this plunge, the Ion and Neutral Mass Spectrometer (INMS) was given two hours of a favorable spacecraft orientation to measure the density and composition of neutral particles in that region; the purpose is to study the relationship between Saturn’s rings and the planet’s atmosphere. The Radio and Plasma Wave Science instrument (RPWS) and the Cosmic Dust Analyzer CDA also made direct-sensing observations. Cassini's Radar instrument rode along with CDA to make its own ring observation, and ISS took a special image of Saturn's rings looking from the inside out.

Saturday, June 17 (DOY 168)

Speeding outbound from Saturn again now, CDA made a dust survey, and RPWS observed the auroral source of Saturn's kilometric-wavelength (low-radio-frequency) radiation. During this busy observing period, the Magnetospheric Imaging Instrument (MIMI) collected data for seven hours, and UVIS observed the abundance of hydrogen in the solar wind. This kind of UVIS observation can utilize a wide variety of pointing conditions while other instruments are making observations, and was repeated on Monday.

UVIS looked back at Saturn's dark southern auroral zone for 4.5 hours, with CIRS and INMS riding along. Next, UVIS watched the rings for nearly six hours using its solar port, to observe a solar ring occultation – the Sun passing behind Saturn's rings. VIMS rode along.

Ground-based astrophotography has enjoyed technical improvements over the years. NASA's Astronomy Picture of the Day today features a superb image of Saturn taken from Earth's surface, with the planet's shadow barely visible on those wide-open rings: https://apod.nasa.gov/apod/ap170617.html.

Sunday, June 18 (DOY 169)

UVIS stared for one hour at Saturn's southern aurora, and then ISS turned to Saturn's small, active moon Enceladus, and monitored its south-polar plume for 14.5 hours; UVIS, CIRS, and VIMS rode along. Next, since Cassini was climbing out into the vicinity of Titan's orbit again, CDA conducted a survey of E-ring particles to sense how Titan affects their distribution.

NASA featured Cassini in another Astronomy Picture of the Day today. This time, it was actually a video consisting of a fast-moving mixed bag of images set to music:https://apod.nasa.gov/apod/ap170618.html.

Monday, June 19 (DOY 170)

ISS imaged Saturn’s fainter rings, the G ring and the E ring, at high-phase illumination for 6.7 hours today. This means those particular rings were back-lit by the Sun, revealing their smallest particles; CIRS and VIMS rode along.

Part of Saturn's broad A ring, and the thin, ever-changing strand of F ring, show how they're affected gravitationally by Saturn's moons, in this image featured today: /resources/17691.

Tuesday, June 20 (DOY 171)

UVIS spent 3.5 hours watching the bright blue star Kappa Orionis while it set into, and became occulted by, Saturn's high atmosphere; ISS and CIRS rode along. This occultation obtained data on the vertical profiles of temperature, and the signatures of some hydrocarbon species, in Saturn's largely unexplored thermosphere.

The Deep Space Network (DSN) communicated with and tracked Cassini on eight occasions this week, using stations in California and Australia. A total of 16 individual commands were uplinked, and about 1,700 megabytes of science and engineering telemetry data were downlinked and captured at rates as high as 142,201 bits per second.

Wrap up:

Cassini is executing its set of 22 Grand Finale Proximal orbits, which have a period of 6.5 days, in a plane inclined 62.1 degrees from the planet's equatorial plane. Each orbit stretches out to an apoapsis altitude of about 1,272,000 km from Saturn, where the spacecraft's planet-relative speed is around 6,000 km/hr. At periapsis, the distance shrinks to about 2,500 km above Saturn's visible atmosphere (by comparison, Saturn is about 120,660 km in diameter), and the speed is around 123,000 km/hr.

The most recent spacecraft tracking and telemetry data were obtained on June 21 using one of the 34-meter diameter DSN 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/anomalies.

The countdown clock in Mission Control shows 86 days until the end of the Mission.

This page offers all the details of the Mission's ending: <https://saturn.jpl.nasa.gov/mission/grand-finale/overview/>
Milestones spanning the whole orbital tour are listed here:
Information on the present position and speed of the Cassini spacecraft may be found on the "Present Position" page at:
To unsubscribe from Cassini Spacecraft Updates or to subscribe with a different email address, visit:
For comments and questions, please contact Cassini Public Engagement at:

This illustration shows Cassini's path up to mid-day June 20.