Spitzer Space Telescope Discovers Largest Ring Around Saturn

http://www.jpl.nasa.gov/news/news.cfm?release=2009-150

NASA Space Telescope Discovers Largest Ring Around Saturn
Jet Propulsion Laboratory
October 06, 2009

PASADENA, Calif. -- NASA's Spitzer Space Telescope has discovered an
enormous ring around Saturn -- by far the largest of the giant
planet's
many rings.

The new belt lies at the far reaches of the Saturnian system, with an
orbit tilted 27 degrees from the main ring plane. The bulk of its
material starts about six million kilometers (3.7 million miles) away
from the planet and extends outward roughly another 12 million
kilometers (7.4 million miles). One of Saturn's farthest moons,
Phoebe,
circles within the newfound ring, and is likely the source of its
material.

Saturn's newest halo is thick, too -- its vertical height is about 20
times the diameter of the planet. It would take about one billion
Earths
stacked together to fill the ring.

"This is one supersized ring," said Anne Verbiscer, an astronomer at
the
University of Virginia, Charlottesville. "If you could see the ring,
it
would span the width of two full moons' worth of sky, one on either
side
of Saturn." Verbiscer; Douglas Hamilton of the University of Maryland,
College Park; and Michael Skrutskie, of the University of Virginia,
Charlottesville, are authors of a paper about the discovery to be
published online tomorrow by the journal Nature.

The ring itself is tenuous, made up of a thin array of ice and dust
particles. Spitzer's infrared eyes were able to spot the glow of the
band's cool dust. The telescope, launched in 2003, is currently 107
million kilometers (66 million miles) from Earth in orbit around the
sun.

The discovery may help solve an age-old riddle of one of Saturn's
moons.
Iapetus has a strange appearance -- one side is bright and the other
is
really dark, in a pattern that resembles the yin-yang symbol. The
astronomer Giovanni Cassini first spotted the moon in 1671, and years
later figured out it has a dark side, now named Cassini Regio in his
honor. A stunning picture of Iapetus taken by NASA's Cassini
spacecraft
is online at http://photojournal.jpl.nasa.gov/catalog/PIA08384 .

Saturn's newest addition could explain how Cassini Regio came to be.
The
ring is circling in the same direction as Phoebe, while Iapetus, the
other rings and most of Saturn's moons are all going the opposite way.
According to the scientists, some of the dark and dusty material from
the outer ring moves inward toward Iapetus, slamming the icy moon like
bugs on a windshield.

"Astronomers have long suspected that there is a connection between
Saturn's outer moon Phoebe and the dark material on Iapetus," said
Hamilton. "This new ring provides convincing evidence of that
relationship."

Verbiscer and her colleagues used Spitzer's longer-wavelength infrared
camera, called the multiband imaging photometer, to scan through a
patch
of sky far from Saturn and a bit inside Phoebe's orbit. The
astronomers
had a hunch that Phoebe might be circling around in a belt of dust
kicked up from its minor collisions with comets -- a process similar
to
that around stars with dusty disks of planetary debris. Sure enough,
when the scientists took a first look at their Spitzer data, a band of
dust jumped out.

The ring would be difficult to see with visible-light telescopes. Its
particles are diffuse and may even extend beyond the bulk of the ring
material all the way in to Saturn and all the way out to
interplanetary
space. The relatively small numbers of particles in the ring wouldn't
reflect much visible light, especially out at Saturn where sunlight is
weak.

"The particles are so far apart that if you were to stand in the ring,
you wouldn't even know it," said Verbiscer.

Spitzer was able to sense the glow of the cool dust, which is only
about
80 Kelvin (minus 316 degrees Fahrenheit). Cool objects shine with
infrared, or thermal radiation; for example, even a cup of ice cream
is
blazing with infrared light. "By focusing on the glow of the ring's
cool
dust, Spitzer made it easy to find," said Verbiscer.

These observations were made before Spitzer ran out of coolant in May
and began its "warm" mission.

NASA's Jet Propulsion Laboratory, Pasadena, Calif., manages the
Spitzer
Space Telescope mission for NASA's Science Mission Directorate,
Washington. Science operations are conducted at the Spitzer Science
Center at the California Institute of Technology, also in Pasadena.
Caltech manages JPL for NASA. The multiband imaging photometer for
Spitzer was built by Ball Aerospace Corporation, Boulder, Colo., and
the
University of Arizona, Tucson. Its principal investigator is George
Rieke of the University of Arizona.

For additional images relating to the ring discovery and more
information about Spitzer, visit http://www.spitzer.caltech.edu
http://www.spitzer.caltech.edu/spitzer and http://www.nasa.gov/spitzer
..

Whitney Clavin 818-354-4673
Jet Propulsion Laboratory, Pasadena, Calif.


J.D. Harrington 202-358-5241
NASA Headquarters, Washington


2009-150