Scientists have been speculating about what we would find in the space between Saturn and its innermost rings, and the Cassini probe is finally putting those hypotheses to the test. A recent course correction has sent the spacecraft skimming along the clouds of Saturn, and the team has found this previously unexplored region of space to be much more empty than they expected.
Cassini has been exploring Saturn and its moons since 2004, but it’s running low on fuel now. That means it’s time for NASA to take some risks with the spacecraft to study new parts of the planet. They call it Cassini’s Grand Finale, a series of close orbits passing between the planet and its rings, a gap measuring just 1,500 miles (2,000 kilometers). One of the reasons Cassini didn’t venture into this space before was the risk of damage from dust particles. The dust particles are only 1 micrometer across, but can cause damage to the probe’s instruments when they impact at high speed. Mysteriously, Cassini has found very low concentrations of dust particles in this region.
Cassini sent back data from its first swing through the gap last week, and it made another pass this week. Cassini used its 13-foot high-gain antenna as a shield to protect itself from impacting dust particles during the first flyby. This allowed scientists on the ground to track how much dust is hitting Cassini using its radio and plasma wave science instrument. NASA converted the raw data output of that instrument to an audio waveform. Each impact causes a pop or crackle interrupting the usual signal. That makes it straightforward to quantify the dust Cassini is encountering.
In its old orbit outside Saturn’s rings, the probe was hit by hundreds of dust particles every second. Inside the rings, that number dropped to single digits. Scientists aren’t sure why yet, but it’s clear some property of Saturn and its rings is clearing dust from this region. It’s either falling down into the planet or being pushed up into the D ring. The video above shows the transition from higher latitudes to the ring gap on the April 26th pass.
Considering the oddly low concentration of dust particles, NASA opted not to use the antenna as a shield during the second trip through the gap. Several upcoming orbits will put Cassini closer to the inner rings where dust concentration could be higher again. For those passes in late May, NASA will again use the antenna as a shield. The team will continue looking after Cassini until September 15th, when the spacecraft will enter Saturn’s atmosphere and disappear forever.
source : https://www.extremetech.com/extreme/248825-cassini-finds-saturns-ring-gap-emptier-expected