3 Apr 2017

On Tuesday, April 4, NASA will hold a press conference to unveil the beginning of Cassini’s last mission segment, called the Grand Finale, a series of 22 orbits plunging between the main rings and the planet’s clouds that will begin in late April. Cassini has been orbiting Saturn since 2004 and sending incredible images of the planet, its rings, and its moons back to earth. On September 15, 2017, Cassini’s mission will end with a dive into Saturn’s upper atmosphere.

In late 2016 Cassini began its Ring Grazing Orbits, a prelude to the Grand Finale in which it takes a series of 20 orbits past the outer edge of Saturn’s main ring system. The resulting images of the rings and moons are some of the best ever seen, including the recent images of the moons Daphnis, some Daphnis images can be found here: Daphnis and Pan.
In January of this year, the first of these closest-ever images from Cassini were released, showing ring features like straw and propellers caused by clumping particles and small moonlets in never-before-seen detail. Matt Tiscareno, senior research scientist at the SETI Institute, is a participating scientist and imaging team associate for Cassini and planned some of these images. More information about these images can be found here.

"These close views represent the opening of an entirely new window onto Saturn’s rings,” Matt explained at the time, “and over the next few months we look forward to even more exciting data as we train our cameras on other parts of the rings closer to the planet."
In February, Cassini captured images of Saturn’s A ring showing a propeller feature, nicknamed Santos-Dumont. This was Cassini’s first targeted flyby of a propeller. Propellers are structures inside Saturn’s rings caused by moons, and it’s estimated that there may be several dozen. The images captured were from opposite sides of ring, one sunlit, and the other backlit, allowing scientists more information about how the moonlet impacts the ring. In March, another propeller feature, nicknamed Earhart, was also imaged. More information can be found here and here.

Learning about phenomena in Saturn’s rings such as straw and propellers helps us to understand other disk-shaped systems, including newly forming solar systems. Rings can also be used to sense other phenomena, such as the interior structure of Saturn or the bombarding influx of meteoroids. Finally, the rings can yield clues to the history and origin of Saturn itself.
These results from the Ring Grazing Orbits are just a foretaste of the bounty expected from the Grand Finale, which includes detailed maps of Saturn’s gravity and magnetic fields, directly measuring the mass of the rings by how hard they pull on Cassini as it flies past, directly sampling icy ring particles, and yet more ultra-close images of Saturn’s rings and also of Saturn’s clouds.

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(A) With help from the public, members of NASA's Cassini mission have chosen to call the spacecraft's final orbits the "Cassini Grand Finale."