NASA Space Telescope Discovers Largest Ring Around Saturn
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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_
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.
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
and
http://www.nasa.gov/spitzer
