Space & Astronomy/Space and Astronomy (October 1993).iso/pc/text/jplnews2/1396.pr

Text File | 1993-05-03 | 6KB | 125 lines

PUBLIC INFORMATION OFFICE
JET PROPULSION LABORATORY
CALIFORNIA INSTITUTE OF TECHNOLOGY
NATIONAL AERONAUTICS AND SPACE ADMINISTRATION
PASADENA, CALIF. 91109. TELEPHONE [phone]

Contact:  Franklin O'Donnell

FOR IMMEDIATE RELEASESeptember 30, 1991


        Thirty years ago last spring, researchers slewed the
metal skeleton of a giant dish antenna toward a spot in the sky
and beamed a pulse of radar energy across tens of millions of
miles of space.
        Some five minutes later, a faint echo of that signal
was received by a second antenna, several miles to the north in
California's Mojave Desert.  The experiment had captured the
first radar echo bounced off another planet, Venus.
        In 1991, researchers are using a similar technique to
bounce signals off of Saturn's moon Titan, hundreds of millions
of miles distant in the outer solar system.  By snagging an
elusive echo from the surface of Titan -- shrouded by a dense
atmosphere boasting organic chemicals possibly like those that
led to life on the Earth -- they may be able to tell if Titan is
partially covered by oceans of ethane, as many scientists
believe.
        Those experiments -- in 1961 and 1991 -- represent the
earliest attempts and most sophisticated recent efforts in the
field of ground-based planetary radar.
        A symposium marking the 30th anniversary of the
technique is being held October 2 at the California Institute of
Technology in Pasadena, California, sponsored by NASA's Jet

Propulsion Laboratory.
        "Radar astronomy was the godfather of the planetary
space program," said Dr. Nicholas Renzetti, manager of JPL's
Telecommunications and Data Acquisition Science Office and
organizer of the Caltech symposium.
        Although such radar experiments can provide nowhere
near the detailed data on planets sent back by exploration
spacecraft, the ground-based technique offers one approach for
scientists when no spacecraft is available.
        By counting how long the radar signal took to return
from Venus in the 1961 tests at JPL's Deep Space Network at
Goldstone, California, researchers were able to measure precisely
the distance between Earth and Venus.  That in turn offered the
best-ever estimate of the astronomical unit, or AU -- the
standard unit of astronomical measure based on the distance
between Earth and the Sun.
        Researchers also found that Venus -- cloaked by
perpetual clouds -- rotates in a retrograde direction about once
every eight months.  That fact was confirmed the next year when
JPL's Mariner 2 made the first flyby of Venus in August 1962.
        In later years, researchers at other institutions used
various other dish antennas around the world to conduct radar
studies, among them Lincoln Laboratory in Massachusetts, Jodrell
Bank at Manchester in the United Kingdom, and various sites in
the Soviet Union.
        The largest such dish on Earth -- the AreciboObservatory in Puerto Rico -- was used by scientists to map the
terrain of Mercury, Venus and Mars.
        Planets have not been the only targets for radar
studies.  Using the giant Arecibo dish, researchers have bounced
radar off of asteroids to help determine their orbits -- and, in
some cases, even their spin rates.  Radar was also used to show
for the first time that comets have a solid nucleus.
        Today the most sensitive radar studies are made not
with a single dish antenna but with a network of such antennas
arrayed together.  In many current experiments, scientists beam a
radar signal into space from JPL's Goldstone site in the
California desert and receive the bounce hundreds of miles away
at the National Radio Astronomy Observatory's Very Large Array in
Socorro, New Mexico.
        That technique is currently being used by researchers
in an attempt to resolve some of the surface features of Saturn's
moon Titan.  Masked by an opaque haze and orbiting the Sun a
billion miles from Earth, Titan appears featureless to telescopes
on Earth.  Even the instruments of JPL's Voyager spacecraft
provided only limited information on the moon during their flybys
in 1980 and 1981.
        Contrasts in "brightness" of radar echoes received in
June 1989 suggest that continents or some similar features may
exist in the oceans of ethane that scientists believe may cover
the surface of Titan.  Although Titan's environment is not
hospitable to human-type life, its atmosphere appears rich in

organic chemicals like those that led to life on Earth.
Scientists are particularly interested in studying Titan to
understand better conditions on the early Earth.
        Titan and its parent planet, Saturn, will be the
destination of Cassini, a NASA mission with the European Space
Agency to be launched in the mid-1990s.  Clues from ground-based
radar studies may help to shape the investigations that the
Cassini spacecraft will carry out.
        Speakers at the Pasadena symposium will include:
        -- Prof. Solomon W. Golomb, University of Southern
California, "The First Touch of Venus";

        -- Dr. Donald B. Campbell, Cornell University, "The
Exploration of Venus by Radar";

        -- Dr. John K. Harmon, Arecibo Observatory, Puerto
Rico, "Radar Observations of Mars and Mercury";

        -- Dr. Steven J. Ostro, JPL/Caltech, "Asteroid Radar
Astronomy";

        -- Prof. Von R. Eshelman, Center for Radar Astronomy,
Stanford University, "Early Radar Astronomy at Stanford";

        -- Prof. Duane O. Muhleman, Caltech, "Goldstone-Very
Large Array Observations of Titan."

        JPL's ground-based radar studies are sponsored by
NASA's Office of Space Science and Applications with support from
the Office of Space Operations.
#####
Note to Editors:  Journalists are invited to attend the symposium
October 2.  For more information, contact JPL's Public
Information Office at [phone].


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