The possibility that such a body of water once existed was suggested by features in Viking images that were interpreted by a number of researchers as remnants of ancient coastlines.
During 1998, MSSS scientists Michael Malin and Kenneth Edgett targeted about 2% of the MOC images in places that would test shorelines proposed by others in the scientific literature.
The MOC images have a resolution five to ten times better than Viking provided. With this closer inspection, none of these features appears to have been formed by the action of water in a coastal environment.
Their analysis was published this week in Geophysical Research Letters, in a paper entitled, "Oceans or Seas in the Martian Northern Lowlands: High Resolution Imaging Tests of Proposed Coastlines."
"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. Edgett, a staff scientist at MSSS.
"The MOC images we took last year do not show any coastal landforms in areas where previous researchers--working with lower resolution Viking images--proposed there were shorelines."
As presented in the Geophysical Research Letters paper, the analysis focused on four different areas that had been proposed as coastlines. One of these areas is northwest of the great volcano, Olympus Mons.
Viking images of the linear feature separating the western margin of the Lycus Sulci from the lower elevation smoother Amazonis plains led some researchers to conclude that the two surfaces were in contact along a cliff.
The proposed cliff faces toward the smooth plains, and thus it was suggested that this might be the kind of cliff that forms from erosion by waves in a body of water as they break against a coastline.
"Even on Earth, looking for ancient shorelines from the air or space is a challenge," said Dr. Malin. "But, despite the difficulties in identifying ancient coastlines remotely, we believe these MOC 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."
While the suggestion that Mars at one time had oceans cannot not 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.
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 MOC 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.
Additional details and more images from the Malin and Edgett paper can be found at Shorelines
Selected Mars Headlines at SpaceDaily.com