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Record-breaking revelations from Venus.

Two record-breaking discoveries -- unveiled in a single day -- offer compelling evidence of Venus' geologic activity, both past and present.

On the morning of Aug. 30, researchers announced that radar images of Venus revealed the solar system's longest channel, an ancient trough longer than the Nile River. Hours later, at a hastily called press conference, the same team announced an even more dramatic finding: Other images showed that Venus suffered a massive landslide sometime in the past several months, providing the first confirmation of current geologic activity on a planet other than Earth.

Jeffrey Plaut of the Jet Propulsion Laboratory in Pasadena, Calif., says he discovered the landslide while comparing two radar images of Aphrodite Terra, an equatorial plateau. The Magellan spacecraft took one of the images last November and the other in July during its second trip around Venus. Placed side by side under a stereoscope, the images should have merged to form a three-dimensional view of a cliff and steeply sloping valley, with bright areas representing the most jagged regions. But a bright patch at the base of the valley, clearly visible in the July image, did not appear in the earlier picture.

Plaut interprets the patch as a massive heap of rocks, roughly 1 mile wide and 4 miles long, that fell from the cliff at some point during the eight-month interim. A third, more recent Magellan image also shows the feature, he says.

Plaut suggests that the landslide may have been triggered by an underground disturbance, such as a "Venusquake," or by a fracture originating at the planet's surface. It probably released as much energy as a magnitude 5 earthquake, he calculates. Though exciting, the discovery that Venus continues to experience geologic upheavals isn't surprising, he adds, since previous eidence suggests the planet has undergone many volcanic eruptions during the past several million years. Plaut says he expects Magellan to capture other such events as it continues to map Venus.

Magellan's other radar revelation emerged in images taken in August. The unusually long channe, stretching across the plains of Venus for 4,200 miles, begins just above the equatorial highlands in a region west of Atla Regio and follows a smoothly curving, northward course toward a large basin called Atalanta Planitia. Soviet spacecraft spied sections of the trough in 1984, but only with Magellan's higher resolution could researchers gauge its full extent, says project scientist Steve Saunders of the Jet Propulsion Laboratory.

Magellan had previously mapped similar, shorter channels on the Venusian plans. Many of these terminate at lava flows, suggesting they were carved out by molten lava from a volcanic eruption, Saunders says. But it's difficult to understand how a lava flow could have remained fluid long enough to create a channel as extensive as the newly discovered one, he adds.

In a rugged terrain of ridges and impact craters, the remarkably uniform width of this trough -- which averages 1.1 miles across -- poses another puzzle, says Saunders. He speculates that the region may have been far smoother when the lengthy channel originally formed.
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Title Annotation:geological activity
Author:Cowen, Ron
Publication:Science News
Date:Sep 7, 1991
Words:508
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