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The Venusian landslide that wasn't.

Forget that report about evidence of a recent landslide on Venus. Scientists now say they misinterpreted radar images taken by the Magellan spacecraft, which orbits the planet.

Comparing Magellan images of an inclined region associated with a plateau called Aphrodite Terra, recorded last November and again in July, researchers had found a striking difference. A bright line in the November image, thought to be a fracture, seemed to have evolved into a bright patch in the July picture. Scientists interpreted the bright area, often an indicator of rough terrain, as a massive heap of rocks that had fallen sometime in the previous eight months (SN: 9/7/91, p.149). The finding appeared to offer the first confirmation of current geological activity on a planet other than Earth.

Jeffrey Plaut of the Jet Propulsion Laboratory in Pasadena, Calif., who discovered the bright patch, now attributes the feature to image distortion. Such distortion occurs when the angle of the detector (relative to the vertical) is less than or equal to the incline of the steeply sloped area.

Such conditions prevailed both times that Magellan flew by Aphrodite Terra. In July, because Magellan's viewing angle was smaller than the area's incline, the craft orbited closer to the top of the hill than to the bottom. Thus it received radar echoes from the top sooner. This translated into an image in which the top appeared as if it were near the bottom. The patch may be an artifact of the misplaced signals. Plaut says.

Because Magellan's viewing angle last November matched the region's slope, echoes from the top and bottom arrived simultaneously. Researchers mistakenly interpreted the single bright line that these echoes formed as a fracture, Plaut says. Though radar still indicates the area contains a few fallen rocks, he says the rubble likely rolled down the slope long ago.
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Title Annotation:radar evidence from Venus was misinterpreted
Publication:Science News
Date:Oct 26, 1991
Words:307
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