Cassini 'CAT scan' maps clumps in Saturn's rings
NASA/JPL NEWS RELEASE
Posted: May 22, 2007
Saturn's largest and most densely packed ring is composed of tightly packed clumps of particles separated by nearly empty gaps, according to new findings from NASA's Cassini spacecraft.
These clumps in Saturn's B ring are neatly organized and constantly colliding, which surprised scientists.
"If you were flying under Saturn's rings in an airplane, you would see these flashes of sunlight come through the gaps, followed by dark and so forth. This is different from flying under a uniform cloud of particles."
Because previous interpretations assumed the ring particles were distributed uniformly, scientists underestimated the total mass of Saturn's rings. The mass may actually be two or more times previous estimates.
"These results will help us understand the overall question of the age and hence the origin of Saturn's rings," said Josh Colwell, assistant professor of physics at the University of Central Florida, Orlando, and a team member of the Cassini ultraviolet imaging spectrograph. A paper with these results appears in the journal Icarus.
Scientists observed the brightness of a star as the rings passed in front of the star on multiple occasions. This provided a measurement of the amount of ring material between the spacecraft and the star.
"Combining many of these occultations at different viewing geometries is like doing a CAT scan of the rings," said Colwell. "By studying the brightness of stars as the rings pass in front of them, we are able to map the ring structure in 3-D and learn more about the shape, spacing and orientation of clusters of particles."
"At any given time, most particles are going to be in one of the clumps, but the particles keep moving from clump to clump as clumps are destroyed and new ones are formed," added Colwell.
In the dense B ring, the classical cloud model of the rings predicted that particles collide about twice per hour on average. "Our results show that the particles in the B ring spend most of their time in almost continuous contact with other particles," said Colwell. These clumps may act like super-sized particles, changing the way the rings spread due to collisions.
The clumps are seen in all regions of the B ring that are not opaque. One surprising aspect of the measurements is that the clumps in the B ring are broad and very flat, like big sheets of particles. They are roughly 10 to 50 times wider than they are thick. Scientists are also surprised that the B ring clumps are flatter and have smaller spaces between them than those found in the neighboring A ring.
The Cassini-Huygens mission is a cooperative project of NASA, the European Space Agency and the Italian Space Agency. The Jet Propulsion Laboratory, a division of the California Institute of Technology in Pasadena, manages the Cassini-Huygens mission for NASA's Science Mission Directorate, Washington. The Cassini orbiter was designed, developed and assembled at JPL. The ultraviolet imaging spectrograph was built at, and the team is based at the University of Colorado, Boulder.