Saturn equinox uncovers hidden dimension to planet's icy ring

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Washington, September 22 (ANI): NASA scientists have captured the setting of the Sun on Saturn's rings, called equinox, in a series of striking Cassini images, uncovering a hidden dimension to this fabled disk of icy debris and highlighting new ring phenomena in the process.

The new images have given excited Cassini scientists a truly unique and revealing glimpse into the physical processes underlying the rings' architecture and time-variability.

At the exact moment of equinox, which occurs twice every Saturn year (or once every 14.8 Earth years), the Sun is directly overhead at the equator and illuminating the rings directly edge-on.

But, a few months before and after this moment, and especially during the four days surrounding exact equinox, the Sun's rays are only skimming the ring plane, significantly darkening the rings, and disclosing out-of-plane structures by making these features anomalously bright and causing them to cast long shadows.

It is these novel lighting conditions surrounding Saturn's August 11, 2009, equinox that have made possible the bounty of recent discoveries in a slate of images released by the Cassini imaging team.

According to imaging team leader Carolyn Porco in Boulder, Colorado, "This has been a moving spectacle to behold, and one that has left us with far greater insight into the workings of Saturn's rings than any of us could have imagined. We always knew it would be good. Instead, it's been extraordinary."

In one unexpected equinox discovery, imaging scientists have uncovered evidence for present-day impacts onto the rings.

Bright, and hence elevated, clouds of tiny particles, sheared out by orbital motion into streaks, up to 3,000 miles (5,000 kilometers) long, have been sighted in the A and C rings.

These clouds - very likely thrown up by impacts - rising above the dark ring plane are more directly catching the Sun's rays during equinox, and are hence well lit and easily visible by contrast.

By the brightness and dimensions of the streaks, scientists estimate the impactor sizes at roughly one meter, and the time since impact at one to two days.

These equinox data now lend more confidence to the impact interpretation of earlier Cassini images, taken in 2005, showing similar streaks in the C ring.

In the 2005 images, the impactors are likely much smaller than one meter, and yet have left a visible ejecta cloud.

All together, these observations are heralded as the first visual confirmation of a long-held belief that bits of interplanetary debris continually rain down on Saturn's rings and contribute to their erosion and evolution. (ANI)

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