Saturn’s Surprises 
Unpredictability was the only predictable aspect of the data sent back by 
the Voyager 1 spacecraft from this giant planet 
by Andrew P. Ingersoll 
Scientists awaiting the Voyager 1 en- 
counter with Saturn in November 1980 
were concerned that the second giant 
planet might not be as interesting as the 
first (see "By Jove,” Natural History , 
May 1980, describing Voyager’s en- 
counter with Jupiter). Saturn’s famous 
rings might be featureless. The surfaces 
of its satellites might reveal no record 
of geologic activity. A uniform haze 
might hide the colorful swirling clouds 
on the planet. And the atmosphere of 
Titan, Saturn’s largest moon, might 
prove to be disappointingly thin. But 
Saturn was not a disappointment, its 
richness proving once again that new 
worlds are worth exploring. 
As planets go, Saturn and Jupiter are 
in a class by themselves. They are not 
massive enough to be stars, although 
they are made of the same elemental 
mixture that makes up the stars and the 
sun. They shine by reflected light, as 
the other planets do, yet they also emit 
appreciable amounts of stored internal 
energy. Like the sun, they are gaseous 
objects without solid surfaces on which 
to land a spacecraft. Saturn is less mas- 
sive than Jupiter and colder. Both have 
rings and more than a dozen satellites. 
Together they account for more than 
90 percent of the solar system’s mass 
outside the sun. And the study of these 
great planets not only teaches us about 
our own world and its history but also 
allows us to test our model of solar sys- 
tem formation. 
Perhaps the most interesting and 
special feature of Saturn is its system of 
rings. These are not solid sheets but bil- 
lions of particles, small satellites, in 
fact, orbiting around the planet. Long 
ago, collisions between the particles 
eliminated most out-of-plane motion as 
well as motion toward and away from 
Saturn. Thus, from afar the rings ap- 
pear perfectly flat and circular. Earth- 
based observations suggest that the 
particles range from one to ten feet in 
diameter and have water-ice surfaces. 
Several rings are visible from the earth. 
Starting farthest from Saturn, these are 
the A ring, followed by a narrow, 
semitransparent “gap” called the Cas- 
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