http://SaturnianCosmology.Org/ mirrored file For complete access to all the files of this collection see http://SaturnianCosmology.org/search.php ========================================================== *Evidence Mounts for Ancient Martian Ocean * *By Greg Clark * Staff Writer posted: 05:33 pm ET 09 December 1999 The vast lowlands that cover most of Mars' northern hemisphere have long posed an interesting puzzle for scientists: Dry river channels that appear to have carried more water than the greatest rivers on Earth run into a wide empty basin that is exceedingly flat and apparently dry. During the past decade a handful of planetary geologists have achieved notoriety by proposing that an ancient ocean likely covered most of the planet's northern hemisphere. They have argued that surface features show evidence of ancient coastlines around the perimeter of the northern basin -- a proposal that has generated controversy since it was advanced. The claims have been difficult to substantiate because they were based on interpretation of images taken by orbiting spacecraft -- an inexact and often subjective exercise. But now, a team of scientists from Brown University is announcing that evidence from the Mars Global Surveyor supports the idea that a wide ocean did once cover the northern third of the planet. The findings are published in this week's issue of the journal /Science/. The mounting evidence invigorates the prospect that a planet other than Earth may once have had conditions favorable to the formation of life. In this topographic portrayal of Mars, an ocean occupies the northern lowlands, as they might have been one to three billion years ago. The Tharsis region, with its numerous volcanoes, is seen in the central part of the globe. Credit: NASA Mars Global Surveyor Project; MOLA Team. Rendering by Peter Neivert, Brown University. Until recently, there has been no way to check whether or not features that might appear to be coastlines were actually that, said James Head, a planetary geologist at Brown, who leads the research team. "Nobody had good data to be able to test the idea and now with the laser altimeter we do," Head said. "We have a lot of good information, we can take pictures, we can look at the topography, we can test a lot of the ideas," that have been put forth. The Mars Orbiter Laser Altimeter is one of the primary instruments aboard the Mars Global Surveyor. It can measure altitude of surface features with great precision, allowing scientists to develop detailed topographical maps of Mars. Head and his colleagues analyzed two proposed coastlines that were suggested by geologist Tim Parker in papers published in 1989 and 1993. Parker, who works at NASA's Jet Propulsion Laboratory, noticed in images from the Viking orbiter that certain features that appeared to encircle Mars' northern basin resembled lakeshores on Earth. He detected linear features that appeared to alternate between beaches and sea cliffs he said. After detailed study, he mapped two lines that he believes were shores of the ancient ocean at two different levels. The diagram above shows a topographical map of Mars' northern hemisphere on the right. Cool colors represent low elevations. The highest land features are shown in red. The outlines, designated Contact 1 and Contact 2, represent two coastlines proposed by Parker and colleagues. Credit: NASA Mars Global Surveyor Project; MOLA Team. Because any coastline would stand at the same elevation along its entire length, Head and his team measured Parker's proposed coastlines, which were named Contact 1 and Contact 2. One of those coastlines appears to have too much variation in elevation to be a coastline, but the other was surprisingly level, Head said. Over the entire several thousand miles of proposed coastline, the elevation varies by only a few hundred meters, on average. "It shows a lot of flatness over a significant part of the planet. And where we do see variation, we have reason to believe that there was subsequent change in topography," Head said. In addition, Head's team analyzed the roughness of the terrain above and below the proposed coastlines. If an ocean did exist, the underwater surface would tend to be smooth. "We found that on all scales, the topography below Contact 2 was smoother than above Contact 2," he said. The team also calculated the volume of water that would have existed in an ocean with the proposed shoreline and found it to be between the minimum and maximum estimates of water on Mars. "Those three things are consistent with the idea that an ocean once existed," Head said. "It doesn't prove it, but it says to me, 'Boy, we really need to be looking at this a lot more seriously and finding more ways to test it.' " While Parker admits that he feels somewhat vindicated by the conclusions of Head's study, he said he is continuing his work analyzing images of the surface. He is now studying high-resolution images from the Mars Global Surveyor's imaging camera. The argument that an ocean existed on Mars is still controversial, however. In a recent paper published in /Geophysical Resource Letters/, planetary scientist Mike Malin offers a differing interpretation of the origin of features that others call a shoreline. Malin is principal investigator for the Mars Orbiter Camera, which is on board the Mars Global Surveyor. Victor Baker, a planetary geologist at the University of Arizona who, along with Parker, was an early advocate of the northern ocean idea, said the new study strengthens the case for a northern global ocean. "It's another set of clues that can be put together, the way a detective puts together clues that he would find at a crime scene," Baker said. "A whole lot of things hang together in a way that looks like they are causally related. So you really have to begin asking the question, 'Is it just a capricious act of nature that makes it look that way, or are they really related?' I think it all hangs together in a way that deserves some attention." http://space.com/