Cassini finds Saturn's ring gap dust-free

As the Cassini spacecraft continues diving between Saturn and its rings, data collected during its first pass has already surprised NASA scientists.

The Cassini spacecraft has returned incredible images of Saturn and its moons. In this image, the planet’s rings dwarf its icy moon Mimas, seen below the rings to the left.
Credit: NASA/JPL-Caltech/Space Science Institute

The gap between Saturn and its rings appears relatively dust-free, according to unexpected results obtained by the Cassini spacecraft.

"The region between the rings and Saturn is 'the big empty,' apparently," says Cassini Project Manager Earl Maize. "Cassini will stay the course, while the scientists work on the mystery of why the dust level is much lower than expected."


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The spacecraft collected the data on 26 April during the first of 22 dives between Saturn and its rings it is making as part of the mission’s Grand Finale. Cassini has been studying Saturn and its moons since 2004, and in September 2017 will purposely crash into Saturn’s atmosphere, capturing images and data right up until its final moments.

This latest package of data has surprised scientists at NASA’s Jet Propulsion Laboratory, as it suggests the gap is less dusty than expected.

Had it been dustier, Cassini’s main antenna would have doubled as a shield to protect it during future dives, affecting how the spacecraft could collect data. But this latest data suggests there is no expected obstacle that could damage the spacecraft during the next 21 dives. However, four of the dives will pass through the innermost edges of Saturn’s rings, requiring the antenna to be used during those passes.

Cassini’s Radio and Plasma Wave Science (RPWS) instrument was used to detect dust particles during the dive. These detections are converted into the sound of pings, pops and crackles for NASA scientists to study. They had expected to hear lots of sound as Cassini passed the ring plane inside the gap, but whistle and squeaks were heard instead. These whistles and squeaks were expected and are created by the charged particle environment around Saturn, which the RPWS instrument is designed to detect.


A video showing data collected by Cassini’s Radio and Plasma Wave Science instrument as it dove through the gap between Saturn and its rings. A lack of cracks and pops in the sound indicates the gap is relatively dust-free.
Credits: NASA/JPL-Caltech/University of Iowa

Analysis of this data suggests Cassini only encountered a few particles as it crossed the gap, and none larger than particles found in smoke, which are about 1 micron across.

"It was a bit disorienting, we weren't hearing what we expected to hear," says William Kurth, RPWS team lead at the University of Iowa. ”I’ve listened to our data from the first dive several times and I can probably count on my hands the number of dust particle impacts I hear."

Cassini will next cross through the ring plane on 2 May 2017 at 7:30pm (UTC).

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