NASA Space Telescope Discovers Largest Ring Around Saturn

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Whitney Clavin 818-354-4673
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J.D. Harrington 202-358-5241
NASA Headquarters, Washington
j.d.harrington@nasa.gov

NEWS RELEASE: 2009-150 Oct. 6, 2009

NASA Space Telescope Discovers Largest Ring Around Saturn

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.

An artist's concept of the newfound ring is online at
http://www.nasa.gov/mission_pages/spitzer/multimedia/spitzer-20091007a.html .

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/spitzer and http://www.nasa.gov/spitzer .

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