Saturnian Shadow Looms Across Rings

Glancing back at Saturn two weeks after orbital insertion. Image Credit: NASA/JPL

Two weeks after orbit insertion, Cassini glanced back at Saturn, taking in the entire planet and its expansive rings. Currently it is summer in Saturn’s southern hemisphere. Notable here is the bright spot located near the planet’s southern hemisphere, where the line from the day and night side of the planet meets. The angle of illumination hints at Saturn’s tilt relative to the Sun.

The banner image was taken in visible red light with the Cassini spacecraft wide angle camera on July 13, 2004, from a distance of about 5 million kilometers (3.1 million miles) from Saturn. The Sun-Saturn-spacecraft, or phase angle of this image is 95 degrees. The image scale is 299 kilometers (186 miles) per pixel. Contrast has been enhanced slightly to aid visibility.

The dark shadow of Saturn’s southern hemisphere spreads across the planet’s rings all the way to the Encke gap. Close inspection of the shadow’s left-most extension reveals the penumbra, the blurry region in which ring features are only partially illuminated. A viewer within the penumbra would see the Sun partially eclipsed by Saturn. Gaps in the rings are caused by a resonant gravity connection between the thirty one moons and the dust halo that surrounds Saturn. Saturn itself has often been compared to a mini-solar-system, since most dust aggregation models for planets and stars involve similar disks with orbital sweeping. The other gas giants like Jupiter and Uranus also have rings but much fainter than the signature characteristic of the sixth planet from the Sun.

The image (right) was taken with the Cassini spacecraft narrow angle camera on June 21, 2004, from a distance of 6.3 million kilometers (3.9 million miles) from Saturn through a filter sensitive to visible green light. The image scale is 37 kilometers (23 miles) per pixel.

Cassini’s six month orbit around the enormous planet will take the spacecraft far away from Saturn in an elliptical departure and return path. During these extended trajectories, much scientific data is collected about the magnetic fields surrounding this unusual world. One particularly intriguing field that Cassini hopes to shed light on centers on why Saturn has such an unusual pole. Unlike other planets, Saturn’s magnetic torus (or donut-shaped field) is observed to rotate at a different rate than the plaent itself. Such models for the magnetosphere tend to act as gigantic turbines of rotating electrical and magnetic energy, an observation that leaves planetary scientists wondering where the driving force comes from and also where the generated energy dissipates. During Cassini’s nominal six-month orbit, its magnetic boom will try to measure detailed shapes for this massive planetary turbine.

The Cassini-Huygens mission is a cooperative project of NASA, the European Space Agency and the Italian Space Agency. The Jet Propulsion Laboratory, a division of the California Institute of Technology in Pasadena, manages the Cassini-Huygens mission for NASA’s Office of Space Science, Washington, D.C. The Cassini orbiter and its two onboard cameras were designed, developed and assembled at JPL. The imaging team is based at the Space Science Institute, Boulder, Colo.

Related Web Pages

Space Science Institute
Chronology of a Scientific Safari
Ring Recycling
Lord of the Rings
Long, Strange Trips
Titan’s Icy Bedrock
Saturn– JPL Cassini Main Page
Alien Landers: Extreme Explorers Hall of Fame