No ring around Saturn moon, study shows

Washington, Aug 7 (ANI): Challenging earlier observations, researchers at Cornell University in New York have claimed that Saturn's small moon Rhea doesn't really have any solid structures encircling the natural satellite.

While it was believed that Rhea had solid rings surrounding it, the new study of optical images has failed to detect any signs of structures encircling the natural satellite.

Rhea orbits within Saturn's magnetic field, which creates a bubble of charged particles-ions and electrons-around the planet.

During a 2005 flyby of Rhea, scientists working with NASA's Cassini spacecraft expected to see a dip in their readings where the moon's surface intercepted the particles.

The craft's readings did show the moon's wake, but they also revealed several unexpected dips in particle detections just outside the moon's diameter.

The best possible explanation seemed to be that something physical-a ring of debris around Rhea-was blocking the ions and electrons from reaching Cassini.

However, analysis of images taken by Cassini between 2008 and 2009 failed to turn up any evidence for rings around the Saturn moon.

"We're pretty confident that there is no solid material orbiting the moon," National Geographic News quoted astronomer Matthew Tiscareno of Cornell University in New York, as saying.

The researchers analysed 65 Cassini images of Rhea, some of which were taken with the sun behind the craft and some with the sun more or less in front of Cassini.

"Those two geometries probe different particle sizes, because dust tends to scatter light forward whereas larger particles tend to reflect light backward," explained Tiscareno.

Instead, the pictures showed nothing illuminated around Rhea, disproving the ring hypothesis-although the new study doesn't shed any light on what was responsible for the 2005 observations.

"It's a real mystery. I think we make a strong case that it's not a ring of solid material around the moon. As for what it is, that's for the magnetospheric community to figure out," said Tiscareno.

The new findings are detailed in a recent issue of the journal Geophysical Research Letters. (ANI)