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Mars valleys point to rainy red planet

A network of valleys discovered on Mars show that the red planet was likely once covered by a vast ocean that fed a humid, rainy climate, according to according to
prep.
1. As stated or indicated by; on the authority of: according to historians.

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 research published Monday.

Debate has raged for decades over whether Martian valleys resulted from water erosion -- caused by humidity and rainfall -- or through groundwater-sapping erosion, which can happen in cold and dry conditions.

The comparative lack of river networks on the Martian surface supported theories that rain was unlikely, but mapping based on topographic data from NASA NASA: see National Aeronautics and Space Administration.
NASA
 in full National Aeronautics and Space Administration

Independent U.S.
 satellites has found that the valley network is at least twice as extensive as previously estimated.

The shape and distribution of the valleys is even more telling, and makes it "hard to imagine" that they could have been caused by anything but rainfall, said co-author Wei Luo, a geography professor at Northern Illinois University Coordinates:  .

The valleys are deeper and more common in the areas closest to the coast of what scientists believe was once a vast northern ocean.

This indicates that they were caused by erosion from clouds which formed over the ocean and dumped the bulk of their rain on the windward side of the mountains, he said.

"Once we looked at the global distribution (of the valley network) we found there is a limit on the southern end of it and most of the concentrated, high density area is close to the hypothesized northern ocean boundary," Luo said in a telephone interview.

"We calculated the estimated depths of the valleys and we see that they get shallower as you go north to south."

Rain, said Luo, "would be mostly restricted to the area over the ocean and to the land surfaces in the immediate vicinity, which correlates with the belt-like pattern of valley dissection seen in our new map.

"The southernmost regions of Mars, located farthest from the water reservoir, would get little rainfall and would develop no valleys."

The study appears in the Journal of Geophysical Research Journal of Geophysical Research is a publication of the American Geophysical Union. JGR was formerly titled Terrestrial Magnetism from its founding by the AGU's president Louis A. .

Luo is co-author of the report along with Tomasz Stepinski, a staff scientist at the Lunar and Planetary Institute The Lunar and Planetary Institute (LPI) is a NASA-funded research institute, dedicated to studies of the solar system, its evolution and formation. The Institute is part of the Universities Space Research Association, located in Houston, Texas.  in Houston, Texas.
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Author:AFP
Publication:AFP American Edition
Date:Nov 24, 2009
Words:349
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