Saturn: Through a Glass Brightly

Saturn’s Translucent Rings

Saturn’s translucent ring detail. Click for larger view. Saturn is the only planet less dense than water (about 30 percent less). In the unlikely event that a large enough ocean could be found, Saturn would float in it.
Credit: NASA/JPL

Saturn’s ring shadows appear wrapped in a harmonious symphony with the planet in this color view from the Cassini spacecraft.

Saturn and its rings would nearly fill the space between Earth and the Moon. Yet, despite their great breadth, the rings are a few meters thick and, in some places, very translucent. This image shows a view through the C ring, which is closest to Saturn, and through the Cassini division, the 4,800-kilometer-wide gap (2,980-miles) that arcs across the top of the image and separates the optically thick B ring from the A ring.

The part of the atmosphere seen through the gap appears darker and more bluish due to scattering at blue wavelengths by the cloud-free upper atmosphere. More transparent sections, like the Cassini Division (just inside the A ring) or the inner C ring, are relatively warmer than the opaque outer A and middle B rings.


Saturn rings in shadow. Image Credit: NASA/JPL

The different colors in Saturn’s atmosphere are due to particles whose composition is yet to be determined. This image was obtained with the Cassini spacecraft narrow angle camera on July 30, 2004, at a distance of 7.6 million kilometers (4.7 million miles) from Saturn. Cassini is too close to the planet and hence no pictures of the unlit side of the rings are available.

Around 1655, the Dutch scientist, Huygens first recognized that Saturn was "girdled by a thin, flat ring, nowhere touching it." The lettering scheme, "A through F", refers to the historical order of the ring divisions’ discoveries, and does not relate easily to their distance from Saturn. Gaps in the rings are caused by a resonant gravity connection between the thirty-plus 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.

With more stunning images, the Cassini spacecraft continues to highlight the icy debris of Saturn’s wispy rings along with its icy satellites. Cassini is conducting a four-year orbital mission, circling Saturn 77 times and cruising by more than 50 close encounters (and another dozen or so more-distant encounters) with the planet’s moons. Color variations in Saturn’s rings have previously been seen in Voyager and Hubble Space Telescope images. Cassini images show that color variations in the rings are more distinct in this viewing geometry than they are when seen from Earth. In the 1980s, two Voyager spacecraft flew by Saturn as did Pioneer 11 in 1979. Those fly-by missions raised tantalizing questions that can now be addressed by Cassini’s planned four year tour. Scientists have waited 25 years for an opportunity to answer these questions.

Related Web Pages

Saturn Edition, Astrobiology Magaz.
Saturn’s Rings in UV
Cassini Closes In on Saturn

Saturn– JPL Cassini Main Page
Lord of the Rings
Space Science Institute, Imaging Team Boulder, Colorado
Saturn: The Closest Pass
Voyager Image Query Form