Cassini has uncovered a wealth of data on Saturn’s rings
NASA’s Cassini spacecraft, now conducting its final orbits between Saturn and its rings, is plunging further than ever into the giant planet’s atmosphere. Over the last 13 years studying the Saturn system, the spacecraft has discovered a wealth of information about the planet’s rings.
Data sent back by the probe has revealed the rings formed through numerous processes rather than via a single mechanism. Observations have even provided scientists with insight into both the formation of planets around young stars and the formation of galaxies.
A key finding is that there are numerous ways of forming rings around planets. Saturn’s many moons play major roles in the rings’ formation and structure. The planet’s G-ring as well as two new rings discovered by Cassini in 2006, named the Janus-Epimetheus ring and the Pallene ring, are made up of materials expelled from moons that were hit by meteorites.
The E-ring, which is spread out over a large area and not highly concentrated, is composed of water ice particles from Enceladus delivered via jets.
One of two potentially habitable moons orbiting Saturn, Enceladus has a global subsurface ocean from which geysers have been seen erupting through its cracked, icy surface. Images taken by Cassini show long, narrow structures that clearly originate from the moon’s geysers.
Some rings, such as the F-ring, fall under the gravitational interaction of nearby moons. Satellite Prometheus regularly perturbs this ring, as it does the thin ringlets that traverse the 202-mile (325-kilometer) wide Encke gap in the A-ring.
Both Prometheus and the F-ring have eccentric orbits around their parent planet. Another small moon, Pan, keeps the Encke gap it orbits in open by gravitationally influencing nearby ring particles.
When NASA’s twin Voyager spacecraft flew by Saturn in 1980 and 1981, its images revealed strange features among the rings that scientists labeled “spokes” because they flare out much like spokes on the wheels of bicycles.
Data sent back by Cassini showed the spokes to be ice particles that interact with Saturn’s magnetic field. Electrostatic charges related to the angle of sunlight the rings are exposed to lift these particles above the rings. A seasonal phenomena, the spokes show up around Saturn’s two equinoxes but vanish at the time of its two solstices.
In 2010, Cassini spotted a new class of small moons that create propeller-shaped features within individual rings. Scientists now believe the processes that formed these tiny moons are similar to the processes by which planets form around young stars.
“Observing the motions of these disk-embedded objects provides a rare opportunity to gauge how the planets grew from, and interacted with, the disk of material surrounding the early Sun,” said Cassini imaging team lead Carolyn Porco.
While Saturn’s rings were once thought to be flat, Cassini revealed they are actually bumpy, in some cases hosting fluffy vertical structures as tall as the Rocky Mountains. Located at the outer edges of Saturn’s A and B rings, these structures were detected by the spacecraft through analysis of light and shadow patterns caused by the varying angle of the Sun over time.
Wave patterns or oscillations that distort the B-ring’s outer edges are similar to those found in spiral galaxies such as the Milky Way as well as in protoplanetary disks around newborn stars.
These oscillations are caused by energy released during small movements of the ring particles, which create and feed waves that can grow to hundreds of kilometers in diameter. Cassini’s instruments were able to discern patterns in these waves by studying the interplay of light and shadow in the rings’ vertical structures.
After an August 10 gravitational assist from Titan, Cassini embarked on the 18th of its 22 Grand Finale orbits. On Monday, August 14, its Ion and Neutral Mass Spectrometer (INMS) conducted the first ever direct sampling of Saturn’s upper atmosphere.
Laurel Kornfeld is an amateur astronomer and freelance writer from Highland Park, NJ, who enjoys writing about astronomy and planetary science. She studied journalism at Douglass College, Rutgers University, and earned a Graduate Certificate of Science from Swinburne University’s Astronomy Online program. Her writings have been published online in The Atlantic, Astronomy magazine’s guest blog section, the UK Space Conference, the 2009 IAU General Assembly newspaper, The Space Reporter, and newsletters of various astronomy clubs. She is a member of the Cranford, NJ-based Amateur Astronomers, Inc. Especially interested in the outer solar system, Laurel gave a brief presentation at the 2008 Great Planet Debate held at the Johns Hopkins University Applied Physics Lab in Laurel, MD.