NASA and Cassini discover ‘the big empty’ between Saturn and its rings

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After the first of Cassini’s 22 dives, the spacecraft has already beamed back surprising data about Saturn.

NASA’s Cassini spacecraft embarked on its grand finale last week, diving through the 1,200-mile-wide gap between Saturn and its rings in a maneuver that brought the spacecraft closer to the ringed planet than any man-made object had been before. The spacecraft sent back a bunch of striking images along the way (see the gallery above). Scientists knew they’d also get some unique data from the dive but they weren’t sure what exactly would be beamed back. And they were surprised by what they discovered — essentially nothing.

“The region between the rings and Saturn is ‘the big empty,’ apparently,” Earl Maize, project manager for the Cassini mission, said in a statement. In other words, there was hardly anything floating around out there. “Cassini will stay the course, while the scientists work on the mystery of why the dust level is much lower than expected.”

The discovery has puzzled scientists who specialize in planetary rings but it relieved a lot of stress for Cassini engineers, who were preparing for the spacecraft’s 21 subsequent dives. Since the region had so little dust, the engineers won’t have to reposition Cassini’s main antenna as a shield as they did during the first dive. This will make it easier for the spacecraft to communicate with Earth without compromising the safety of its instruments.

Ring scientists were confident that the region would not have dangerously large particles but were unsure whether it would still contain smaller pieces of debris. Though the spacecraft’s Radio and Plasma Wave Science (RPWS) instrument detected hundreds of particles per second in the ring plane, it only detected a few while crossing the planet-ring gap. The video below shows what that barren landscape sounds like.

“It was a bit disorienting — we weren’t hearing what we expected to hear,” said RPWS team lead, William Kurth. “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 took its second dive through the ring plane on May 2, during which time the engineers pointed its camera at the rings while rotating the spacecraft to calibrate its magnetometer.