NASA doesn’t have to mind the gap when it comes to its Cassini spacecraft exploring Saturn up-close and personal — it turns out there isn’t much going on in the space between the planet and its rings, and that has left some scientists scratching their heads.

“Cassini engineers are delighted while ring scientists are puzzled that the region appears to be relatively dust-free,” the space agency’s Jet Propulsion Laboratory said.

Read: Photos Between Saturn and Its Rings

Experts had worried about dust when Cassini took the first of 22 planned dives toward Saturn, between the planet and the rings, so much so that they had turned a dish-shaped antenna on the spacecraft to act as a shield, cutting off its line of communication with Earth for a tense almost 24 hours. But Cassini emerged from the blackout and sent back photos and data from the 1,200-mile-wide gap, including images of Saturn’s atmosphere from angles and heights scientists never before have had. The data show when it comes to dust particles, there’s nothing to fear as Cassini makes another dive Tuesday at 3:38 p.m. EDT (12:38 p.m. PDT).

Particles don’t sound dangerous, but when Cassini is moving 77,000 mph, a well-aimed particle can do a lot of damage.

“The region between the rings and Saturn is ‘the big empty,’ apparently,” Cassini project manager Earl Maize at JPL said in the statement. That opens up a case to be solved: “Cassini will stay the course while the scientists work on the mystery of why the dust level is much lower than expected.”

Cassini will start transmitting data from its second dive back to Earth Wednesday.

One of the spacecraft’s instruments “detected the hits of hundreds of ring particles per second when it crossed the ring plane just outside of Saturn's main rings, but only detected a few pings” when it passed through the gap the first time, NASA said. The space agency released audio showing the difference. The former crossing is full of pops that make it sound like an old record with the music missing. The crossing between Saturn and its rings instead sounds full of whooshes and squeaks that are a hallmark of “the charged particle environment that the instrument is designed to detect.”

“The big empty” might have been unexpected, but Cassini has been teaching scientists lots of new things about Saturn and its moons since heading to the outer solar system several years ago. The spacecraft detected hydrogen on the moon Enceladus that potentially could be an energy source for certain alien life forms. It has also sent back thousands of images and will keep going until it runs out of fuel and is sent into Saturn’s atmosphere to burn up later this year. Its final months of observations and dives toward Saturn is being called its “grand finale.”

See also:

What Earth Looks Like From Saturn

5 Cool Moons to Explore in Our Solar System