Space & Astronomy/Space and Astronomy (October 1993).iso/pc/text/jplnews2/1346.pr

Text File | 1993-05-03 | 4KB | 75 lines

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

FOR RELEASE FRIDAY JAN. 25, AND THEREAFTER
    The Magellan spacecraft mapping the surface of Venus with
imaging radar has swept over nearly 55 percent of the planet, an
area comparable on Earth to the distance from Los Angeles to New
Delhi, India.
    Magellan scientists said the radar data provides significant
new knowledge about the surface of Venus and its atmosphere.
    All of the areas mapped show widespread evidence of
volcanism, said Project Scientist Dr. Steve Saunders, along with
evidence of tectonics, the process that produces mountains.
    "Venus and Earth are the only planets in our solar system
that have linear mountain belts," he said. But the mountains on
Venus are not deeply eroded by rainfall and running water as are
the mountains on Earth.
    Magellan also confirmed the number of impact craters that
scientists had expected to find, judging from their earlier
Earth-based radar data.
    The smallest impact craters that have been seen so far on
the surface are about three miles in diameter, which indicates
the dense atmosphere has effectively shielded the surface from
bombardment of smaller asteroids and comets.
    There is also evidence that the poisonous, thick atmosphere
of Venus was not formed recently, Saunders said. Surface images
indicate it may be from 400 million to 800 million years old oreven older. The Venus atmosphere is 90 times heavier than that of
Earth and is composed primarily of carbon dioxide with
significant amounts of sulfuric acid at upper levels.
    Saunders said scientists see in the images that linear
mountain belts are being pulled apart by gravitational forces on
the planet.
    New styles of volcanism have been found and lava channels
hundreds of miles long occur at several places on the plains.
Although lava channels have been found on Earth, none are as long
or as regular as those seen on Venus.
    Another new type of volcanism is being referred to by
scientists as "pancake" domes; these structures appear to be up
to 20 miles across and nearly a mile high and form on the plains.
Scientists believe the domes are formed by an outflow of a pasty,
thick lava, similar to silicon-rich lavas on Earth
    Volcanic domes also form on Earth, but they are much
smaller and form in volcanic calderas, Saunders said.
    The images also reveal indications of turbulent surface
winds on the planet. The evidence is in the form of wind streaks
in the lee of topographical obstacles, such as the small, low
shield volcanoes on the plains.
    "Careful mapping of those wind streaks over the entire
planet may give us meteorological data about circulation of the
atmosphere near the surface," Saunders said.
    To date, there have been 118 days of mapping and 973 orbits.
A total of 819.6 mapping orbits have been received on Earth, 45
percent of the planet's surface, Project Manager Tony Spear said.

    Fifteen days of mapping were lost, as expected, to superior
conjunction, the period last November when Earth and Venus were
on opposite sides of the sun and data transmission between the
two planets was impossible.
    There have been other losses of data since mapping began
last Sept. 15, due to spacecraft problems and difficulties at
the various Deep Space Network stations, Spear said. But of the
area covered by mapping orbits, only 2.4 percent has been lost.
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Editors note:  Three pictures will be released with the story.
The pictures will be available Friday, Jan. 25, at the Jet
Propulsion Laboratory and at NASA Public Affairs Office in
Washington, D.C.