May 2 (UPI) -- NASA scientists expected Cassini to encounter hundreds of dust particles as it flew through the gap between Saturn and its rings. Instead, the probe found "The Big Empty," an area with very few dust particles.
"The region between the rings and Saturn is 'The Big Empty,' apparently," Earl Maize, Cassini project manager at NASA's Jet Propulsion Laboratory in Pasadena, Calif., said in a news release. "Cassini will stay the course, while the scientists work on the mystery of why the dust level is much lower than expected."
Engineers pointed the probe's antenna forwards as a protect mechanism -- a way to protect the probe for collisions with dust particles as it passes between Saturn's upper atmosphere and the gas giant's main rings.
Cassini's antenna features a sensor called the Radio and Plasma Wave Science instrument. When RPWS observations are turned into audio files, collisions with dust particles translate as crackles and pops.
Before Cassini crossed the main ring plane, the probe encountered hundreds of ring particles per second. But once Cassini crossed Saturn's main rings, the whistling was mostly interrupted by pings.
"It was a bit disorienting -- we weren't hearing what we expected to hear," said 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."
The Big Empty is another puzzle for scientists to solve, but it's good news for the Cassini mission. Because it's no longer necessary to protect the probe with a forward-shifted antenna, more of Cassini's scientific instruments will be able to function normally.
Cassini is preparing to make its second of 22 dives -- the probe's "grand finale."
On September 15, at the end of the grand finale phase -- the grand finale's grand finale -- Cassini will make one final dive into Saturn's atmosphere.