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Absent shoreline challenges Mars water theory

Viking mission images of the Acidalia region on Mars shown here were thought to show an ancient shoreline but a closer look offered by Global Surveyor reveals no coastal landforms, scientists say.  

October 4, 1999
Web posted at: 2:21 p.m. EDT (1821 GMT)

(CNN) -- Despite a flood of previous evidence suggesting Mars once was awash with water, high-resolution images from a NASA mapping orbiter show no evidence of ancient ocean shorelines on the red planet.

The images from Mars Global Surveyor, taken in 1998, have a resolution five to 10 times better than those returned by the Viking missions in the 1970s, which scientists said showed remnants of coastlines.

Destination Mars

Now, none of these features appears to have been formed by the action of water in a coastal environment.

"The newer images do not show any coastal landforms in areas where previous researchers --working with lower resolution Viking images -- proposed there were shorelines," said researcher Ken Edgett.

"The ocean hypothesis is very important because the existence of large bodies of liquid water in the martian past would have had a tremendous impact on ancient martian climate and implications for the search for evidence of past life on the planet,"

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Edgett is a staff scientist at Malin Space Science Systems, the institution that built and manages the Mars Orbiter Camera on the spacecraft.

About 2 percent of the Mars Orbiter Camera images were targeted to look in places that would test shorelines proposed by others in the scientific literature.

Looking for ancient shorelines from air or space is a challenge above any planet, said Michael Malin, principal investigator for the camera and head of Malin Space Science Systems.

"Despite these difficulties, we believe these Mars Orbiter Camera images of the proposed shorelines are of a high-enough resolution that they would have shown features indicative of a coastal environment had there been an ancient ocean on Mars," he said.

The results were published in the latest issue of the Journal of Geophysical Research Letters.

Coastline expected at Olympus Mons

Scientists had suspected a coastline northwest of the volcano Olympus Mons. Viking researchers said earlier images suggested a cliff separating the western margin of the Lycus Sulci uplands from the lower-elevation, smoother Amazonis plains.

The proposed cliff looked like the kind that forms on Earth from erosion as waves break against a coastline.

Global Surveyor snapped three high-resolution images of this area. The uplands are roughly textured, while the flat plains appear smoother, Malin said.

The image shows that the contact between the two regions clearly is not a wave-cut cliff, nor are there any features that can be unambiguously identified as coastal landforms, he said.

The hypothesis that Mars once had oceans cannot be ruled out, Malin said.

"It should be understood that there is significant other evidence of water on Mars in the past, both from Mars Global Surveyor and from previous missions," he said.

Global Surveyor is the first mission in NASA's Mars exploration program, managed by Jet Propulsion Laboratory.

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