Cassini Finds Rhythm in Saturn's Rings

Feature January 31, 2008



Cassini Finds Rhythm in Saturn's Rings

Order can be found in the most unexpected places, as demonstrated
by our neighbor three planets down. Two of Saturn's rings have
been found by NASA's Cassini spacecraft to contain orderly lines
of densely grouped, boulder-size icy particles that extend outward
across the rings like ripples from a rock dropped in a calm pond.

"Imagine going to a town that stretches from San Francisco to Los
Angeles and seeing buildings spaced the same distance apart on
every block," said Cassini radio science team member Essam
Marouf of San Jose State University, San Jose, Calif. "All of these
groups of particles within the rings are very close together, and the
space between them is extremely small, only 100 to 250 meters
(320 feet to 820 feet) wide, depending on where they are in the
ring."

Normally, the distances between particles change with their
velocity. In the case of Saturn's rings, the distances between these
ring particles stay relatively equal even though their velocities may
change. This type of pattern is completely new, according to
Marouf.

"This particular feature is the smallest and most detailed of
anything seen in Saturn's rings so far," Marouf said. "In the
chaotic environment of the rings, to find such regularity in the
most cramped areas is nothing short of amazing." The regular
structure can only be found in locations where particles are densely
packed together, such as the B ring and the innermost part of the A
ring.

The unexpected pattern within Saturn's rings may give scientists
some new ideas of what to expect from other similar planets and
solar systems.

The pattern was detected when the radio on board the Cassini
spacecraft sent out three signals toward Earth. The signals crossed
the Saturn's rings, and their frequencies were separated by
scattering from the ring particles. Once the signals were captured
by Earth-based antennas of NASA's Deep Space Network, Cassini
scientists saw a regular pattern in the received signal frequencies.

"The signals showed that the particle groups were arranged in an
unexpectedly regular formation that had 'rhythm within the rings of
Saturn,'" said Marouf. "Each particle is in its own orbit, and
sometimes they collide and move apart as their velocities change.
As a result, you have particles bunched together into dense groups
that extend across the ring in harmony with each other."

The pattern of particles is described as an enormously extended
natural diffraction grating. A diffraction grating has parallel lines
like a picket fence; when light hits this fence, it separates
according to wavelength, from ultraviolet to infrared light.

The same thing happened when Cassini's radio signals hit the
fencelike pattern of ring particles. The signals, sent out in 2005,
were meant to capture a complete view of the rings.

This research appears as a cover story in the Dec. 28 issue of
Geophysical Research Letters.

Written by: Diya Chacko
Media Relations Contact: Carolina Martinez 818-354-9382

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