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Magellan finds wind sculpture on Venus.

The Magellan spacecraft has radar-mapped parts of the Venusian surface more than once, providing researchers with information not apparent from a single image, such as mountain's height, or indications that major surface changes have occurred between snapshots.

At the Lunar and Planetary Science Conference in Houston last week, scientists presented a pair of Magellan images that suggests winds on Venus have played a surprisingly important, and perhaps recent, role in sculpting large-scale features on the planet. The images, from data gathered last year in March and November, show a nearly flat terrain, about the size of Pennsylvania, surrounding the crater Stowe near a highland called Imdr Regio.

In the March image, obtained as Magellan's radar detector faced east, about 25 [degrees] from the vertical, most of the terrain appears dark. But an image taken eight months later, as the detector faced west at about the same angle from the vertical, shows many bright patches, as well as bright bands. The changes may reflect one of two intriguing possibilities, says Jeffrey Plaut of NASA's JEt Propulsion Laboratory in Pasadena, Calif.

The region may consist of an undulating field of small, regularly spaced sand dunes, each no higher than a few meters, sloping to the east. Wind associated with the impact that formed the Stowe crater might have created such structures from pulverized rock, he says. The easterly sloping dunes, unchanged between Magellan snapshots, may account for the brighter November image, says Plaut, since they would reflect radio waves more efficiently toward a detector facing them. But he adds that this interpretation requires the Venusian wind to have sculpted the dunes over an area as big as 264,000 square kilometers.

Alternatively, Plaut says, the differences may stem from an actual surface change. During the months between images, he suggests, gusts of wind may have blown surface soil from most of the region, exposing rockier terrain beneath. Such terrain would reflect more radio waves, resulting in a brighter image.

In new observations confirm this scenario, Plaut notes, then winds on Venus may alter the planet's surface continuously, rather than having acted as a one-shot force. Yet either notion, he adds, seems surprising, since previous instruments had found that relatively flat features on Venus lack the temperature gradient needed to drive strong surface winds, even though fierce winds occur higher in Venus' dense atmosphere.

Image distortion due to Magellan's different viewing angles has at times fooled researchers into identifying unique surface features where none actually existed. But in the present case, the symmetry of the viewing angles from the vertical makes such a mistake unlikely, Plau says.
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Title Annotation:space probe
Author:Cowen, Ron
Publication:Science News
Article Type:Brief Article
Date:Mar 28, 1992
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