Saturn
showed off a new
ring in a snapshot just taken by NASA's Cassini spacecraft.
The
spacecraft, which entered the orbit of Saturn
in July 2004, also revealed other dazzling features of the ringed planet,
including wispy
fingers of icy material stretching out tens of thousands of miles from the
moon Enceladus.
Cassini's cameras took advantage of a 12-hour backlight provided by the Sun,
which was directly behind Saturn. So as Cassini lurked in the shadow of Saturn,
the planet's rings were brilliantly backlit by the passing Sun. Called a solar
occultation, this Sun-Saturn alignment typically lasts only about an hour, but
this time it was a half-day marathon.
The lengthy
illumination of Saturn allowed Cassini
to map the presence of microscopic particles that are not normally visible
across the ring system. This level of detail gave astronomers the sharpest view
yet of Saturn's inner system, including the new ring.
Another
ring
Saturn's
ring system is divided into seven main divisions, each designated by a
letter of the alphabet. From the innermost to outermost ring, the divisions
are: D, C, B, A, F, G and E.
The new
ring is a tenuous feature and lies outside the brighter main rings of Saturn,
but inside the G and E rings.
The ring
coincides with the orbits of Saturn's moons Janus and Epimetheus. Scientists
expected meteoroid impacts on the two moons could kick off moon particles and
inject them into Saturn's orbit. But they were surprised to find such a
distinct ring structure in that region.
Icy
fingers
The 12-hour
backlight session enabled astronomers to see the entire E ring in one view, a
feat that previously required several images of small sections of the ring.
The
snapshot showed Enceladus
sweeping through the E ring, extending wispy, fingerlike projections into the
ring. The scientists suspect the 'fingers' consist of tiny ice particles being
ejected from Enceladus'
south polar geysers and into the E ring.
"Both
the new ring and the unexpected structures in the E ring should provide us with
important insights into how moons can both release small particles and sculpt
their local environments," said Matt Hedman, a researcher working with
team member Joseph Burns, an expert in diffuse rings, at Cornell University in
Ithaca, N.Y.
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