Scientists are baffled by the relatively dust-free space in the approximately 2,000 km-wide region between Saturn and its rings.
This assessment is based on data collected by spacecraft Cassini during its first dive through the narrow gap, according to the U.S. space agency NASA.
"The region between the rings and Saturn is 'the big empty,' apparently," Cassini project manager Earl Maize of NASA's Jet Propulsion Laboratory said in a statement on Monday. "Cassini will stay the course, while the scientists work on the mystery of why the dust level is much lower than expected."
Based on images from Cassini, models of the ring particle environment in the region between Saturn and its rings suggested the area would not have large particles that would pose a danger to the spacecraft.
"These sounds represent data collected between Saturn and its rings. It's quieter than expected," the mission team tweeted on Monday.
After almost 20 years in space, Cassini began what mission planners are calling its "Grand Finale," the final chapter of its remarkable story of exploration, making a series of 22 weekly dives between the rings and the planet. On April 26, the spacecraft successfully completed the first dive between Saturn and its rings.
Cassini's next dive through the the ring plane is scheduled for Tuesday in a region very close to where it passed on the previous dive. As with the first finale dive, Cassini will be out of contact during closest approach to Saturn, and is scheduled to transmit data from this dive on the next day.
Finally, the long-lived spacecraft will make a mission-ending plunge into the planet's atmosphere on September 15.
Launched in 1997, Cassini has been touring the Saturn system since arriving there in 2004. During its journey, Cassini has made numerous dramatic discoveries, including a global ocean within Enceladus and liquid methane seas on Titan. But the mission is drawing near its end because the spacecraft is running low on fuel.
