When NASA’s Cassini spacecraft dove between Saturn and its rings the other day on April 26, there was a significant risk of danger. Scientists weren’t sure how much debris would be in this region, but surprisingly, it turns out there was very little.
This was the closest a spacecraft has ever been to Saturn, with Cassini diving just 3,000 kilometers (1,900 miles) from its cloud tops as part of its Grand Finale phase. Being inside the rings, mission scientists thought they might encounter dust particles that could damage the spacecraft, which was traveling at a relative speed of 124,000 kilometers per hour (77,000 miles per hour).
To ensure the spacecraft survived, they pointed its large 4-meter-wide (13 feet) antenna forwards, used to communicate with Earth, to absorb the impacts. Anything hitting the dish would create a noticeable ping that would let scientists know what was there. And there wasn’t much.
"It was a bit disorienting – we weren't hearing what we expected to hear," said William Kurth, team leader for Cassini's Radio and Plasma Wave Science (RPWS) instrument, one of two in the antenna, in a statement. "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."
You can hear the sound below, made by the RPWS instrument recording the particles striking the antenna. It's eerily quiet.
In fact, Cassini seemed to only hit a few particles, and none were larger than those found in smoke, which are about 1 micron (0.000001 meters) across. This led scientists to call the 2,000-kilometer-wide (1,200 miles) region “the big empty”.
This means that for most of its 21 future dives through this region, Cassini will not need to use its antenna as a shield in this way again, opening up new possibilities for using its instruments. The antenna will be pointed forwards on just four of the dives, those that go closest to the inner edge of the rings.
The next close pass of Saturn for Cassini is taking place today at 3.38pm EDT (8.38pm BST), in a similar region to that explored the other day. The spacecraft won’t be sending data back until tomorrow, though, but judging by the previous images, it should be pretty impressive.