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NEW MARS IMAGES: NO EVIDENCE OF ANCIENT OCEAN SHORELINES

http://www.jpl.nasa.gov

"NEW MARS IMAGES: NO EVIDENCE OF ANCIENT OCEAN SHORELINES

     Scientists studying high-resolution images from NASA's Mars
Global Surveyor spacecraft have concluded there is no evidence of
shorelines that would have surrounded oceans that may have once
existed on Mars.

     One argument that such a body of water once existed was
suggested by features in images from the NASA Viking missions
taken in the 1970s, which were interpreted by a number of
researchers as remnants of ancient coastlines. The images from
Mars Global Surveyor, taken in 1998, have a resolution five to 10
times better than those that Viking provided.  With this closer
inspection, none of these features appears to have been formed by
the action of water in a coastal environment.

     "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," said Dr. Kenneth Edgett, a staff scientist at Malin
Space Science Systems, San Diego, CA, the institution that built
and manages the Mars Orbiter Camera onboard the spacecraft. "The
newer images do not show any coastal landforms in areas where
previous researchers -- working with lower resolution Viking
images -- proposed there were shorelines."

     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.

     "Even on Earth, looking for ancient shorelines from the air
or space is a challenge," said Dr. Michael Malin, principal
investigator for the camera at 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."

     The paper containing these new conclusions was published in
the October 1 issue of the Journal of Geophysical Research
Letters.

     One area that might have been a coastline is located
northwest of the great volcano Olympus Mons.  Researchers looking
at Viking images have suggested that there might be 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.

     Three high-resolution images were taken of this proposed
coastline. The uplands are roughly textured, while the flat
plains appear smoother. The image shows that the contact between
the two regions is clearly not a wave-cut cliff, nor are there
any features that can be unambiguously identified as coastal
landforms, according to Malin.

     "While the suggestion that Mars at one time had oceans
cannot be ruled out, the foundation for the 'ocean hypothesis'
developed in the 1980s on the basis of suspected shorelines
appears now to have been incorrect," Malin concluded. "However,
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. Today, the Mars Orbiter Camera continues
to acquire new high-resolution pictures, each one helping to
search for clues to the very important question of the role of
water in the evolution of Mars."



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