In his last year, Cassini plunged where no spacecraft had plunged before, into the space between Saturn and its rings. Again and again he plunged, for a total of 22 orbits. When collecting data during these dizzying dives, astronomers come to find new information on how tiny moons sculpt and sculpt these rings.
It is, they say, not only a new proof that the rings of Saturn are much younger than the planet, but also a window on the formation of planets in the giant rings of dust and debris that surround the nascent stars.
The new data, collected with the help of four Cassini instruments, show the rings in more detail than ever before.
"It's as if we're still increasing the power over what we could see in the rings – everyone now has a clearer view of what's going on," said Linda Spilker, project scientist. Cassini, from JPL-NASA. "The obtaining of this additional resolution has answered many questions, but there are still so many tempting ones."
They reveal the delicate straw-like textures and clumps in the rings, as well as the patterns produced by the movement of sheep moons, such as Daphnis. Scientists have also established new maps of colors, temperatures and ring chemistry.
This information in turn responds to intriguing questions. For example, a series of streaks generated by impacts in the F-ring – that is, the outermost of the main rings – all have the same length and orientation.
This involves a flock of strike elements in orbit around Saturn, not a swarm of rogue comet debris in orbit around the Sun.
The data also provided new information on Daphnis. The shenanigans of the shepherd's moon in the open path we call Keeler's ditch are already well documented, but new images have revealed thin bands of annular material separating ridges in the wake of the moon.
But not everything is enlightening. Cassini scientists have spotted something that they do not yet understand: three distinct textures – smooth, lumpy and streaked. These features appear in the rings in distinct belts, with sharp and well-defined edges.
The problem is that, until now, textures can not be related to any features of the rings identified so far.
"This tells us that the appearance of the rings is not only a function of the amount of material available," said astronomer Matt Tiscareno of the SETI Institute.
"There must be something different about particle characteristics, perhaps affecting what happens when two annular particles collide and bounce back and forth.
"And we do not know yet what it is."
There was more mystery in ring chemistry, revealed by Cassini's visible and infrared mapping spectrometer.
In the outermost part of the A ring, the spectral map revealed an abundance of weak water ice. This was a surprise because the area is very reflective, which usually indicates a high purity ice-water or a strong ice-water. It's a puzzle.
And the spectral analysis also detected no ice of methane or ammonia in the rings. It's also a headache, because last year scientists discovered, among other organic materials, ammonia and methane that fell from Saturn on its deepest ring.
But it is okay. For even though the probe mission ended almost two years ago, there is still a lot of Cassini data to unravel.
"We're seeing a lot more and getting closer, and we're getting new, more interesting puzzles," said astronomer Jeff Cuzzi of NASA.
"We are moving to the next phase, which involves building new detailed models of the evolution of the rings – including the new revelation from Cassini's data that the rings are much younger than Saturn. "
Better to hurry though. In 100 million years, these glorious rings could be entirely gone.
The search was published in Science.