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FOR RELEASE MONDAY, DEC. 3, OR THEREAFTER


       The Magellan spacecraft, mapping the surface of Venus with imaging radar, has completed imaging about a third of the planet on its primary mission cycle which began Sept. 15.

       The spacecraft went into its three hour and 15 minute orbit around Venus on Aug. 10 following a 15-month long journey from Earth.

       The Magellan science team at NASA's Jet Propulsion Laboratory, working with high resolution mosaics of the planet's surface, have identified mountainous slopes dusted with an unidentified metallic substance which may be iron pyrite, sometimes called fools gold, a line of huge volcanic domes that look like pancakes, and large horseshoe shaped formations that may be unique in the solar system.

       Magellan has completed to date 65 days of mapping, plus 15 days when Venus and Earth were in superior conjunction on opposite sides of the sun.

       There have been 473 mapping orbits but 11.8 orbits were lost. Data from 461.2 orbits were received on Earth. Mapping has covered 118.4 degrees of longitude of the planet, with 93.8 degrees mapped.

       The total area swept by radar mapping is 32.9 percent of the surface of Venus with 26 percent captured in radar data.      If the area is projected on the Earth, the total area would extend from Los Angeles to London with a 22-degree gap over the Atlantic Ocean.

       Mapping has covered much of the large continental area called Ishtar Terra which includes the seven-mile high mountain, Maxwell Montes. Scientists said it may have been formed by the same kind of tectonic compression forces that shaped the Himalayas on Earth.

       The unidentified metallic substance was detected on the slopes of Maxwell. It appears bright in the radar images and if it were seen on Earth scientists might have assumed it is ice or water. The surface of Venus, however, is above 700 degrees Fahrenheit. The substance has been identified only as a metallic material, possibly pyrite, but it also could be hematite or magnetite.

       Some recent image also shows large volcanic craters, lava floods, long trench-like rips in the surface called graben, and horseshoe-shaped features 600 miles long and 300 miles wide surrounding impact craters.

       The images also show high domes of volcanic lava 15 miles in diameter and 2,500 feet high that may have been formed by a viscous form of molten rock.

       The project expects to map about 80 percent of the planet despite problems with the spacecraft. There were two losses of signal in August before mapping began and a 40-minute loss in November.

       Flight controllers said the problem could occur again but changes made in the spacecraft's software, as illustrated by the most recent problem, can be quickly rectified resulting in a minimal time loss.

       The Magellan Project is managed by the Jet Propulsion Laboratory for NASA's Office of Space Science and Applications.


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12/3/90 JJD
#1338