Saturn takes center stage

Posted by Alison Klesman
on Tuesday, October 17, 2017

Cassini scientists meet the press on October 16 to discuss some of the latest findings from Saturn. // Richard Talcott

By Richard Talcott

While most of the astronomical world spent Monday celebrating the incredible discovery of two neutron stars merging, planetary scientists held their own celebration. On the first day of the 49th Division for Planetary Sciences meeting in Provo, Utah, scientists with the Cassini mission to Saturn reported on the latest discoveries to come from the spacecraft before it plunged into the ringed planet’s atmosphere a month ago.

During Cassini’s “Grand Finale,” the spacecraft flew between Saturn’s rings and its cloud tops 22 times. Among the researchers keeping a close eye on the rings during these final orbits was Matt Tiscareno of the SETI Institute. He was observing “propellers” — wakes created in the rings by unseen moonlets. The close passes turned up dozens of new propellers caused by moonlets just 300 to 400 feet (100 meters) across, and also gave the best views yet of six large propellers Cassini has been following for years. The propellers are analogues of planets forming in the disks around newborn stars, and researchers hope that the Saturn observations will deliver insights into the planet-forming process.

Cassini’s camera captured tis panoramic view of Saturn’s rings September 9, just after it crossed the ring plane and less than a week from the mission’s end. // NASA/JPL-Caltech/SSI

Mark Perry from the Johns Hopkins University Applied Physics Laboratory used the close-in orbits to directly sample Saturn’s upper atmosphere. Astronomers have known since the days of Voyager 35 years ago that there are impurities in the upper atmosphere. Most expected it was water “raining” down from the icy rings, but they couldn’t tell without actually scooping up some of the material. Although water does play a role, methane also shows up. No one expected this volatile substance to be abundant in either the rings or in the upper atmosphere. And there appears to be many so-far unidentified heavier compounds lurking in the cloud tops.

Finally, Radwan Tajeddine of Cornell University is reporting on what keeps the rings of Saturn in place. Scientists have long known that an orbital resonance with the moon Mimas creates the sharp outer edge of the bright B ring. But Tajeddine has shown that the outer A ring requires the combined gravitational pulls of seven satellites: Pan, Atlas, Prometheus, Pandora, Janus, Epimetheus, and Mimas. Without all seven acting on the ring particles, the A ring would eventually dissipate into space.

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