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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