ehind Saturn from Cassini's vantage point. With the Sun safely blocked, ISS turned to image the faint rings. Such geometries are conducive to studying ring structures that are dominated by small, micron-sized particles, such as Saturn's innermost D ring, and the outlying G and E rings.
The spectacular images of Atlas went right to the Cassini Raw Images website as soon as they came down to Earth (as do all Cassini's images). Here are some of them, with standard captions: /news/13025/cassini-sees-flying-saucer-moon-atlas-up-close .
News from Cassini about Saturn's moon Enceladus, and related news from the Hubble Space Telescope about Jupiter's moon Europa were the subjects of today's NASA press conference: /news/3024/nasa-missions-provide-new-insights-into-ocean-worlds-in-our-solar-system .
Three additional articles featured Enceladus on the Cassini website today:
Hydrothermal activity /news/13023/hydrothermal-activity .
Free samples /news/13022/free-samples .
The enormous, puzzling E ring /news/13021/put-a-ring-on-it .
Friday, April 14 (DOY 104)
Today is the birthday of Christiaan Huygens, the polymath who correctly surmised the configuration of Saturn’s rings, and discovered its largest moon Titan in 1655, when he was 26 years old.
CIRS spent three hours with the campaign to create a library of moderate wavelength-resolution spectra of various regions in Saturn's rings; VIMS and UVIS rode along. Later, today's occultation experiment involved VIMS tracking the bright red star Alpha Orionis, also known as Betelgeuse; CIRS rode along. The star made a full radial egress behind Saturn's main rings. This was the last science activity stored in the 10-week-long S98 sequence of commands. The command sequence S99, whose uplink last week was captured on video (https://go.nasa.gov/2oq3jnM), took over control of Cassini for the next seven weeks.
The MAPS instruments continued their direct-sensing surveys as the S99 sequence took effect; the Cosmic Dust Analyzer (CDA) looking at dust, the Ion and Neutral Mass Spectrometer (INMS) measuring the atmospheric and ionospheric thermal structure of Saturn, and the Magnetometer (MAG) and the RPWS performing magnetospheric measurements.
ISS undertook the first of three three-hour observations of Saturn's bright crescent limb today, with UVIS and VIMS riding along. The second one took place on the next day, and the third on Sunday. After today's, there was a 11.2-hour VIMS observation of the Saturn globe as it rotated through one Saturn day; CIRS participated. Cassini's view of the looming gas giant is simulated here.
Saturday, April 15 (DOY 105)
During today's communications session with the Deep Space Network, the spacecraft was slowly rolling about its longitudinal axis, so that UVIS could conduct an interplanetary hydrogen survey, while CIRS performed a calibration with cold deep space in its field of view. Next, CIRS spent 12 hours making a mid-infrared map of Saturn’s northern hemisphere, to determine upper troposphere and tropopause temperatures.
Sunday, April 16 (DOY 106)
During the CIRS activity, the spacecraft coasted through apoapsis. This marked the start of Cassini's Orbit #270, which will be the final one in its series of 20 F-ring grazing orbits.
None other than Cassini's view of Enceladus was the subject of NASA's Astronomy Picture of the Day today: https://apod.nasa.gov/apod/ap170416.html .
Monday, April 17 (DOY 107)
CIRS began the day with far-infrared mapping of Saturn’s northern hemisphere, again to measure upper troposphere and tropopause temperatures; VIMS rode along with this 22.3-hour observation, taking images about once every hour.
Late in the day, UVIS and VIMS began 12 hours of daytime observations of Saturn's northern auroral region, with CIRS riding along.
Saturn cloud patterns were the subject of today's featured image: /resources/17645 .
Tuesday, April 18 (DOY 108)
Cassini's final targeted Titan encounter, T-126, is coming up on April 22. This page offers details of the flyby: /news/13019/titan-flyby-t-126-final-close-encounter-gateway-to-the-grand-finale .
The 