The NASA Cassini orbiter ended its 13-year exploration of the Saturn system on September 15, 2017… burning up in the planet’s atmosphere as planned. The UltraViolet Imaging Spectrograph (UVIS) took data through the last moment of the final 22 orbits, which began in April 2017 and brought the spacecraft closer to Saturn than any mission before.
During the six months preceding Cassini’s dramatic finale, UVIS collected valuable information that was too risky to obtain earlier in the mission. These discoveries include the closest images ever obtained of Saturn’s auroras, and the glowing air of Saturn that enveloped the spacecraft during Cassini’s final data transmission, sent a minute before the spacecraft burned up. The final auroral image reveals a never-before-seen bright spot of emission closest to Saturn’s north pole. The final UVIS spectrum shows glowing hydrogen from the atmosphere and nitrogen from the spacecraft’s thrusters, experienced in situ for the first time.
Images, spectra and occultations show a very dynamic system of rings and moons, with unexpected ring structures seen at scales from 1m to 100km. We observed spiral density waves, self-gravity wakes, embedded moons, straw, kittens, propellers, clumps and equinox objects, many that are likely transient. These structures may be created by resonant satellite forcing, self-gravity, collisions of aggregates and compaction in the rings… which are not yet incorporated in any complete model. Nonetheless, I find ecological comparisons helpful, for example, predator-prey systems. This leads to explanations of the ring behavior in terms of the dynamics of non-linear driven systems, with possible implications for similar processes in planet formation.
Although the end of the mission was bittersweet for all involved, Cassini’s “Grand Finale” ensured that its entire payload, including UVIS, contributed awe-inspiring and unique science data right up to its final moments. Cassini deepened our understanding of the universe and heightened our connection to the outer solar system. At its conclusion, it will be remembered as one of the most scientifically rich and impactful voyages yet undertaken.
The NASA and ESA Cassini-Huygens space mission observed the Saturn system and its rings since 2003, with the mission ending in a fiery finish in 2017. UVIS was designed, built, tested, and operated by LASP with the initial NASA contract beginning in 1990. Even though the mission has ended, team members worldwide continue to interpret instrument observations and publish results in scientific journals for years to come.