Shadows and rain from Saturn's rings alter the planet's ionosphere

When Cassini traveled through the shadows of Saturn’s largest and brightest rings (the A and B rings), it measured a drastic drop in the amount of ionized plasma present, meaning the ionosphere got weaker when it was shaded. Though interesting, this is not an entirely surprising. Because ionospheres are produced when ultraviolet light from the Sun strips off charged particles from atoms in the planet's upper atmosphere, it makes sense that Saturn’s ionosphere is weaker when the rings block the incoming sunlight.

However, the team found that even when the planet’s rings veiled Saturn’s ionosphere, there was still measurable activity in the plasma. This indicates that sunlight is not the only thing that influences Saturn's ionosphere. Though researchers are not certain what causes the phenomenon, they theorize that Saturn’s innermost D-ring may be generating “ring rain” — where charged water particles embedded in Saturn’s rings migrate to the ionosphere, keeping the plasma mildly active.

“It is as though the small ice particles in the D-ring suck up electrons from the ionosphere,” said Jan-Erik Wahlund in a press release. “As a result of the coupling, electrical flows of gas to and from the rings along the magnetic field of Saturn cause the greatest variations in density.”

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Since the researchers’ findings were based on just half the data Cassini collected during its Grand Finale of orbits, it is safe to say there is much more left to discover.

“Consider this a prelude of things to come from Cassini,” said Hunter Waite, directory of planetary mass spectrometry at South West Research Institute, in a press release. “Saturn’s ionosphere is much more complicated than anyone could imagine.”

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