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JET PROPULSION LABORATORY
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Contact: Jim Doyle

FOR IMMEDIATE RELEASE                                                June 28, 1994



       The planet Venus is still geologically active in places, even though radar images of its surface indicate that little has changed in the past half-billion years, a scientist working on data from NASA's Magellan mission has found.

       Dr. Suzanne Smrekar, a geophysicist at NASA's Jet Propulsion Laboratory, said her studies, based on Magellan spacecraft altimetry and gravity data, suggest that there are at least two, and possibly more, active hot spots on Venus.

       Her paper, entitled "Evidence for Active Hotspots on Venus from Analysis of Magellan Gravity Data," is to be published later this year in the science publication Icarus. Smrekar earlier presented her findings before a meeting of the Lunar and Planetary Society in Houston, Texas.

       The Magellan spacecraft went into orbit around Venus in August of 1990 and, over the next two years, mapped about 98 percent of the planet's surface with imaging radar. It then began to gather gravity data to help scientists develop a model of the planet's interior.

       Gravity is measured using only the spacecraft's radio signal. This technique allows ground controllers to measure the spacecraft's speed in orbit as it increases in velocity over regions of high density or slows down over regions of lesser density.

       Magellan's altimetry instrument measured the height of features on the surface of the planet.

       The gravity data showed evidence of "top loading" and "bottom loading" at several locations, Smrekar said. Top loading is evidence of a large mass, such as a mountain or volcano, pushing down on the crustal plate. At hot spots, bottom loading indicates an upwelling of less dense and, therefore, hotter material beneath the surface.

       "The matter rises and is pushed upward because it is hot and, thus, less dense," she said. "As it nears the surface, it produces volcanism." The mechanisms are similar to those which occur on Earth and which produce volcanoes like those on Hawaii.

       Earlier data from the spacecraft's imaging radar showed that much of the surface of Venus had been covered in the past by lava flows.

       Smrekar said two regions on Venus -- Atla Regio and Bell Regio -- exhibited clear signatures of both bottom and top loading of the elastic surface.

       The signatures from the data are indicative of an active hot spot at Atla Regio, Smrekar said. Although the loading response is less clear, the data from Western Eistla and Beta Regio also support the interpretation that those areas are underlain by large, hot areas, probably due to active plumes in the mantle beneath the planet's crust.

       At Bell Regio, Smrekar found indications of a late, possibly inactive, evolutionary stage of a low-density layer that is no longer very hot.

       "These early results from a survey of four major volcanic swells on Venus reveal hot spots in different stages of evolution," Smrekar noted in her paper. "Analysis confirms that the Beta, Atla and Western Eistla regions are active hot spots."

       Smrekar said future studies of those areas and other possible hot spots on Venus would continue to improve scientists' understanding of the evolution of hot spots on both Venus and Earth.

       Her work at the Jet Propulsion Laboratory was done under contract to NASA's Office of Space Science.


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6/28/94 JJD
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