Cassini scientists will provide evidence in this week’s issue of Science that the previously labeled ringlets near Saturn’s F ring are instead a single spiral arm surrounding a core ring. No such object has ever before been observed in our solar system.

The F ring is a thin but complex feature beyond Saturn’s more prominent A ring. The imaging team responsible for the discovery used a 360 degree map created from images of the F ring taken by Cassini. The resulting map clearly revealed a continuous spiral circling Saturn. Because the spiral is wrapped so tightly on itself, it appeared to be several distinct ringlets, until the close proximity of Cassini instruments finally reveal its true structure.

The reporting scientists believe a collision between the core F ring and a small moon or moonlet led to a secondary spiral of particles. These collisions may happen frequently, suggesting that the spiral is a transitory structure. The tiny shepherd moon Pandora is set to collide with the core F ring in 2009, an event that could provide more details about the phenomena.

More Information

• Cassini-Huygens Website
  • Saturn’s Rings section

On February 20, 2005, the Cassini spacecraft took a picture of Pandora and Prometheus hard a work shepherding water ice particles and dust into a distinct F-ring unit within Saturn’s larger ring structure.

Historically, three main rings were discovered around Saturn, labeled C, B and A from the inside out. Later, fainter rings and structures within the larger rings were detected and labeled with additional letters from the alphabet. The F-ring is located outside of the A-ring. It is now known that many of these rings are in fact made up of even thinner ringlets. A large gap called the Cassini Division between B- and A-ring is not completely devoid of particles and was a concern when Cassini first arrived at the Saturn system in 2004. Cassini passed through the gap with no damage and has been hard at work studying the complex system of rings and gaps around Saturn ever since.

Many of the moons in the system interact with the rings to create their complex structure. Ringlets may vary slightly from each other in terms of composition and average particle size. Individual grains of primarily water ice in the rings can be as small as microscopic in size or as large as a boulder. The source of material for the rings is not well understood, but evidence suggests the rings are young and made up of material from some of the moons, perhaps through ice volcanoes.

While the rings of Saturn are easily visible to Earth-based telescopes, the amount of material in them is nearly negligible. The rings’ water ice composition and wide range reflects sunlight and give them their majesty. Jupiter, Uranus, and Neptune are also known to have rings, albeit much less dramatic. Scientists will use Cassini to study the rings of Saturn in great detail over the next several years.

More Information

• Cassini-Huygens Mission
  • Saturn’s Rings images
  • Saturn’s Moons section

NASA yesterday released a new image from Cassini of the shadow of Saturn cast across its rings. While a wealth of images have been returned by Cassini in the past few weeks, only a relative few have been processed. The rest remain in raw format awaiting future processing. All images, raw and processed, are available on the Cassini-Huygens website.

The day before, NASA released a false-color image of Titan that brings out the haze layers in its atmosphere. Such images will help scientists better understand the activity in Titan’s atmosphere.

NASA is now releasing a new image from Cassini a day. On May 10, Cassini imaged the shadows of Saturn’s rings on its surface and also the swirling bands of the planet’s atmosphere. Cassini is now officially in the Saturn planetary system as the gravity of Saturn holds more sway than the gravity of the Sun.

It looks like the mission to Saturn is ramping up…today NASA released a new image from Cassini- Huygens less than a week after the last image. The outer visible ring is called the F-ring and in this image from May 1, 2004 you can see the two shepherd moons, Prometheus and Pandora, on either side of ring. The third moon in the image is Epimetheus.