Hans.Moravec%CMU-RI-ROVER@sri-unix.UUCP (01/20/84)
n515 2353 19 Jan 84
BC-SATURN-01-20
By William Hines
(c) 1984 Chicago Sun-Times (Independent Press Service)
WASHINGTON - The rings of Saturn, which have fascinated stargazers
for more than 300 years, are now believed to be much thinner than
previously supposed.
In fact, say two Stanford University scientists, the most prominent
ring is no more than a couple of hundred feet thick, and fainter ones
may be as little as a few inches in thickness.
The new findings, based on radio data from the planetary probe
Voyager 1 more than three years ago, are published in the issue of
the journal Science that goes to readers this weekend.
From the time the Dutch astronomer Christiaan Huygens identified
them in 1659 until 1977, Saturn's rings were thought to be unique in
the solar system if not in the universe. Now it is known that at
least two other major planets, Jupiter and Uranus, also possess ring
systems.
Until deep-space probes flew out to Saturn's vicinity, telescopic
measurements from Earth set one kilometer (roughly 3,300 feet) as the
probable thickness of the rings. Preliminary data from the spacecraft
Pioneer 11 (Sept. 1, 1979) and Voyagers 1 (Nov. 12, 1980) and 2 (Aug.
26, 1981) reduced the estimated maximum thickness to about 100 meters
(330 feet).
Now, say Howard A. Zebker and G. Leonard Tyler of Stanford's Center
for Radar Astronomy in the Science article, new evidence indicates
that the rings are, at most, a few dozen yards thick. ''Putting it in
human terms,'' Tyler said in a telephone interview, ''the thickness
of the A ring could easily pass between the goal posts at opposite
ends of a football field.
''The thickness of the C ring could probably pass between the
uprights of a single set of goal posts.''
The new evidence, they explained, emerged from analysis of radio
signals sent back by Voyager 1 after it had passed the Saturnian ring
system and was in a position to transmit through the rings back to
hugh dish-shaped antennas on Earth.
Saturn's A ring, the first discovered to be identified as a distinct
feature and the brightest of all the rings, is about 6,750 miles
wide. It circles the planet's equator at a height of 40,500 to 47,250
miles above the clouds that make up Saturn's visible surface.
If the Zebker-Tyler measurements are correct, the gossamer thinness
of Saturn's rings is almost incomprehensible. It is the equivalent of
a sheet of material two miles wide and only x00 the thickness of
ordinary plastic household wrap.
How can something so insubstantial be visible from Earth--even
through a telescope--over distances that are never less than about
800 million miles?
High reflectivity is the answer. Tyler said most scientists believe
the particles in the rings are practically pure ice. Saturn's rings
are tilted several degrees off the plane in which the planets circle
the sun. At various times during the 29.5 years it takes Saturn to
circle the sun, they are seen from different angles. When they face
the Earth edge-on, the rings are invisible.
END
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