Planetary Science Seminar Winter-2018

assini ended its spectacular 13-year mission at Saturn with a two-part farewell, during which it obtained the sharpest and highest-fidelity images ever taken of Saturn’s rings. From December 2016 to April 2017, the spacecraft executed 20 near-polar orbits that passed just outside the outer edge of the main rings; these “Ring-Grazing Orbits” provided the mission’s best viewing of the A and F rings and the outer B ring. From April to September 2017, the spacecraft executed 22 near-polar orbits that passed between the innermost D ring and the planet’s clouds; this “Grand Finale” provided the mission’s best viewing of the C and D rings and the inner B ring. We will review the discoveries made by high-resolution imaging of the main rings during these maneuvers. Topics will include: 1) Sharply defined belts with differences in degree and character of clumpiness, which are probably an index for particle properties and interactions; 2) Unprecedentedly detailed images of propellers, which are local disturbances in the ring created by an embedded moon; and 3) Abundant color images of impact ejecta clouds, which constrain the population of decimeter-to-meter-sized meteoroids in Saturn’s vicinity as well as the particle-size distribution of the ejecta, and thus the fracture properties of ring material.