Saturn Moon loses its ring
Ker Than
Electron data suggested ring around Rhea, but camera doesn't lie.
Until this week Saturn's small moon Rhea was the only known solid space
object thought to have a ring.
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Saturn’s moon Rhea (file image). Image courtesy NASA |
(Other known ringed bodies, such as Saturn, are mainly gaseous.) But
a 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," said astronomer Matthew Tiscareno of Cornell University in New
York.
Moon mystery comes to light Tiscareno and his team analyzed 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.
National Geographic News |
