Sometimes new discoveries are what you don’t see and hear. Cassini ring scientists were left scratching their heads after the spacecraft’s first deep dive between Saturn’s upper atmosphere and the inner rings.

During the first harrowing dive of Cassini’s Grand Finale, mission controllers positioned the spacecraft’s antenna in front of the spacecraft to act as a shield. This was meant to protect the spacecraft from small ring particles as it flew through the never explored region. These particles are the size of a smoke particle, but even that can do real damage when it’s traveling at thousands of miles per hour.

When scientists received data from the Radio and Plasma Wave Science (RPWS) instrument, they expected to hear hundreds of pops/cracks as tiny ring particles struck the spacecraft. Instead, they heard almost nothing.

“The region between the rings and Saturn is ‘the big empty,’ apparently,” said Cassini Project Manager Earl Maize. “Cassini will stay the course, while the scientists work on the mystery of why the dust level is much lower than expected.”

Here’s a video from last December showing data collected by the RPWS instrument when Cassini crossed the plane of Saturn’s rings. Listen for the cracks and pops, especially around the 30-second mark.

Now, listen to what the same instrument recorded during the first dive on April 26.

William Kurth is the team lead for the RPWS instrument and was surprised when the data made its way back to Earth. “It was a bit disorienting – we weren’t hearing what we expected to hear.”

“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,” Kurth added.

Fun fact: The RPWS instrument doesn’t record ‘sound,’ but scientists can take the detected radio and plasma waves and convert them into sound. The result is an audio file where we ‘hear’ the dust particles hitting the antenna.

It looks like Cassini antenna won’t need to double as a shield for the majority of the spacecraft’s final orbits. Mission controllers still plan to use the antenna to protect the spacecraft for four orbits that take Cassini towards the innermost edge of Saturn’s rings.

Second dive done

Scientists are just waiting for Cassini to reestablish contact with Earth. NASA’s Deep Space Network is expected to reacquire Cassini’s signal in late morning/early afternoon. The spacecraft was on its own for 20 hours during the first dive. Expect a similar timeframe here too.

UPDATE: The DSN in Canberra is receiving a signal from Cassini.

I’ll keep you posted once Cassini is talking to Earth again. And when the next set of stunning images are released.

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