Dust-free space near Saturn baffles Cassini scientists

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Scientists, coming to grips with recent data from the Cassini spacecraft, are baffled by the lack of dust in the 2,000 kilometre-wide region between Saturn and its rings.

Data collected by Cassini during its first dive through the region on 26 April shows the region to be largely free of any sort of debris.

“The region between the rings and Saturn is ‘the big empty’, apparently,” said Cassini project manager Earl Maize. 

But the unexpected finding has been a boon for the spacecraft’s engineers who now won’t have to shield its saucer shape antenna from damaging dust particles. 

That means Cassini will now be able to collect data and make observations all the way through its next dive through the ring plane. 

“Cassini will stay the course, while the scientists work on the mystery of why the dust level is much lower than expected,” said Maize.

Although engineers had angled the spacecraft during the 26 April dive to protect the four-metre wide antenna, Cassini’s Radio and Plasma Wave Science (RPWS) instrument and magnetometer were exposed.

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An artist’s concept shows how Cassini is able to detect radio signals from lightning on Saturn using its Radio and Plasma Wave Science instrument. Lightning strokes emit electromagnetic energy across a broad range of wavelengths.

As the RPWS hits particles of dust the data are converted to audio format – pops and cracks that cover up the usual whistles and squeaks of waves in the charged particle environment that the instrument is designed to detect. 

The RPWS team expected to hear a lot of pops and cracks on crossing the ring plane inside the gap, but instead, they got whistles and squeaks.

“It was a bit disorienting – we weren’t hearing what we expected to hear,” said William Kurth, RPWS team leader.

“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 cross through the ring plane on 2 May 19:38 UTC.

It is scheduled for another 21 dives – four passing through the innermost fringes of the giant planet’s rings.

NASA has more information about Cassini’s Grand Finale, including images and video, is available at https://saturn.jpl.nasa.gov/grandfinale

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