Douglas Isbell
Headquarters, Washington, DC               May 18, 1995
(Phone: 202/358-1547)

Mary Beth Murrill
Jet Propulsion Laboratory, Pasadena, CA
(Phone: 818/354-6478)

RELEASE:  95-72


SATURN'S RINGS: NOW YOU SEE THEM, NOW YOU DON'T

        The rings of Saturn will all but disappear for a few 
moments on May 22 during a rare astronomical event that will 
allow astronomers to look for new moons and other features that 
are normally obscured by the glare of the dazzling rings.

        Many of the world's major telescopes, including NASA's 
Hubble Space Telescope, will focus on Saturn during the 24-
minute event.

        The phenomenon is known to astronomers as a Saturn ring 
plane crossing. This year and next, the rings will be seen 
edge-on from the Earth's perspective on three occasions -- May 
22 and August 10, 1995, and Feb. 11, 1996.  This event only 
happens about every 15 years.  

	Ring plane crossings provide astronomers with unique 
views of the Saturnian system.  With the rings temporarily 
invisible as viewed from Earth, faint objects near the planet 
are easier to see.  Thirteen of Saturn's 18 known moons have 
been discovered during past ring plane crossings.

        The faint, outermost E-ring also is easier to detect 
when viewed edge-on due to the greater amount of material in 
the line-of-sight.  Thus, observations made over the course of 
the ring plane crossing also can be used to gather new 
information on the thickness of the rings and to search for new 
rings.

        The event is of special interest to scientists and 
engineers at NASA's Jet Propulsion Laboratory (JPL), Pasadena, 
CA, who are fine-tuning the flight path of the Cassini 
spacecraft.  Cassini is scheduled for launch on a mission to 
Saturn in 1997, jointly conducted by NASA, the European Space
Agency and the Italian Space Agency.  Any new data on the location
and density of material in the rings will help the Cassini team 
plan the most advantageous and safest course for the spacecraft 
to take when it flies through the rings upon arrival at Saturn 
in 2004.

        "We're going in awfully close with Cassini," said 
mission scientist Dr. Linda Horn of JPL, "so the more we know 
about the boundaries of the rings, the more confident we'll 
be."   Plans call for the spacecraft to fly through a 15,500-
mile (25,000-kilometer) gap between the F- and G-rings, then 
closely over the broad C-ring.  Later, the spacecraft will make 
several passes through the E-ring.

        Astronomers hope to refine measurements of Saturn's 
small, inner moons during the ring plane crossing.  Better 
estimates of the moons' sizes will be useful in targeting 
Cassini's observations of those satellites, according to Horn.

        Saturn's rings are known to be numerous, dynamically 
complex and made up of countless particles of ice ranging in 
size from boulders to snowflakes, with some rock mixed in.  
They are thought to be the remains of comets, meteoroids and 
possibly small moons that have been captured and torn apart by 
Saturn's gravity. 

        The rings are a prime target for the science 
instruments aboard the Cassini spacecraft, whose mission is to 
study the Saturnian system while orbiting the planet for four 
years.  Cassini also will carry the European Space Agency's 
Huygens Probe to be dropped into the atmosphere of Saturn's 
large moon Titan.  As it parachutes downward, the Huygens Probe 
will return information about Titan's atmosphere and surface.  
In some ways scientists believe Titan resembles Earth as it 
existed in a primordial stage before life developed.

        The Cassini Project is managed by JPL for NASA's Office 
of Space Science in Washington, DC.

                       - end -

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