The smallest of the three rings of Saturn appears to be made of snow and ice balls as large as 30 feet across.
Measurements of the so-called C-ring made by the Voyager spacecraft that flew by Saturn last Wednesday show that the "particles" that make up the ring range in size from three inches to 30 feet. They average three feet in size, which comes as something of a suprise to scientists who expected them to be smaller.
"These are not "particles," Dr. G. Len Tyler said today at the Jet Propulsion Laboratory where the flight of Voyager is being directed. "These are boulders flying around Saturn in some very organized manner."
The information on the rings is amonga massive amount of data that Voyager has sent back to earth from itsencounter with Saturn. The probe has yielded so much data, in fact, and so much of it has been different from what scientists had expected that it wllbe weeks or even months before it is all sorted out. And determination of what it all means will take longer than that.
The measurements of the C-ring were the first taken by Voyager, which beamed a radio signal through the three large rings when it flew behind Saturn late Wednesday night. The way the signals came back scattered back to earth tells scientists how large the ring particles are that do the scattering.
"The same effect is used [by deviceson earth] to measure the speed of baseballs," Tyler said. "Since we know the speed of the particles in the ring, we can use this effect to measure and figure out their size."
Dr. Alan Cook of the Harvard-Smithsonian Center for Astrophysics said that he expects the particles in the A- and B-rings will be smaller than those found today in the C-ring. Cooksaid the two larger rings are thicker and more densely populated than the C-ring, implying that the larger rings are made of smaller particles thatmaybe grinding against each other.
"We don't expect much in the 30-foot size range in the A- and B-rings," Cook said. "We expect things to scaledown in size when we get the results of the radio experiment from those two rings."
The radio signals scattered through the rings do not tell scientists what the rings are made of but ultraviolet measurements strongly suggest they are made of little more than snow and ice. Most of the rings are tinted red, suggesting some kind of cosmic dust might cover the surface of the snow and ice balls.
"The smallest particles in the C-ring are probably pure ice," Cook said. "The larger ones are a mix of snow and ice, with the ice acting as inclusions in the snow."
Cook said the "balls" that make up the ring are not spherical. He said that collisions with other particles and bombardment by cosmic dust probably give the ring particles an irregular and evenjagged shape.
The C-ring has a blue cast to it that the other rings do not have, Cook said which probably means there's more dust on the snowballs in it than those in the other rings. That could be because the C-ring partgicles are farther apart than those in the other rings and don't undergo as much grinding.
"We still don't know what kinds of collisions go on inside the rings," Cook said. "We think the ring particles areelectrically charged from their passage through Saturn's strong magnetic field,which would keep them apart by electrostatic repulsion."
The rings also undergo meteorite bombardment, which serves to keep the ring particles smaller in size and also acts to replenish the rings. The meteorites could be the source of the dust that tints the A- and B-rings red and the C-ring blue.
Besides sending a radio signal through the rings, Voyager also beamed a signal through the atmosphere of Titan, the largest of Saturn's 15 moons and the only moon in the solar system topossess a sizable atmosphere. Stanford's Dr. Tyler said that an early look at the Titan information showed that its atmosphere is at least half again as dense as the earth's and could be as thick as three times that of the earth.
"We have not analyzed all our data and we have not reached the surface of Titan in our data," Tyler said. "But what we are seeing is a deep atmosphere that is almost 100 percent nitrogen.