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Ridges on Mars

The northern plains of Mars is the flattest known region in the solar system. When Viking returned topographic data for the surface of Mars in the 1970s, one-quarter of the surface appeared featureless. The Viking images were accurate only to the nearest kilometer. Now, higher resolution data from the Mars Orbiter Laser Altimeter (MOLA) has returned images that are accurate to the nearest meter. Suddenly the featureless northern plains appear not to be as smooth as scientists once believed.

[At right: This color-enhanced topographic contour map resolves radial ridges at 54°N on the northern plains of Mars. NASA.]

Planetary geologists had attributed the extraordinary flatness to an ancient ocean. But an article published in the Dec. 24, 1999, Science outlines earlier work on the MOLA images and concludes that the newly visible features are ancient shorelines.
 
More recently, the paleo-shorelines were re-examined by Paul Withers of the University of Arizona and Gregory Neumann of the Massachusetts Institute of Technology — two scientists who don’t believe the features are shorelines at all. Their work, published in the April 5 Nature, supports the theory that the lines are actually tectonic ridges.
 
In some areas the ridges are “radial to obvious centers of volcanism,” including the Tharsis Rise, the Utopia impact basin and the Alba Patera volcano, Withers says. “Topographic profiles taken across the ridges look similar to compressional wrinkles on other terrestrial planets,” he adds.
 
Withers and Neumann’s finding is big news for those who study the geology of Mars. “Viking data showed nothing for this quarter of Mars,” Withers says. “This was a big gap to have in a global model.”

Laura Wright


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