|
Ring around Saturn
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.
NASA finds Saturn 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.
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"
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.
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
|
|
|
