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Show Kenneth S. Edgett, Department of Geology, Arizona State University, Tempe, AZ 85287- 1404. - and - Timothy J. Parker, MS 183- 501, Jet Propulsion Lab., 4800 Oak Grove Dr., Pasadena, CA 91109. FROM THE NORTH AMERICAN GREAT BASIN TO THE PLANET MARS: TAKING LACUSTRINE GEOMORPHOLOGY INTO THE 21ST CENTURY Introduction: The entire planet Mars is presently a desert more arid than any on Earth. The planet appears to have had more water in the past, and some of this water affected the surface geology and geomorphology by carving a variety of channels. Despite the evidence for running water in the martian past, the presence of standing bodies of water ( lakes, oceans) has been a topic of considerable controversy in the past two decades. The issue is still not settled, but evidence has mounted to suggest that lakes and oceans were indeed a major factor in shaping the present geomorphology of the martian surface. Although there remains uncertainty as to whether lakes were present on Mars, major efforts to seek evidence for fossil martian organisms are focused on the search for lake sediments and tufa deposits [ 1]. In 2001 and 2003, the NASA Mars Surveyor Program will launch mobile rovers designed to explore the surface and collect samples for return to Earth. The first set of samples will reach Earth in 2008. The types of landing sites being considered for the ' 01 and ' 03 missions include areas interpreted as ancient lacustrine deposits. Knowledge and experience with the geomorphology of lacustrine features in the North American Great Basin is crucial for identifying lake features on Mars. Martian Lakes and Oceans: Prior to spacecraft exploration of Mars, many early astronomers thought that the low- albedo surfaces on Mars could be seas or lakes; others considered these to be vast tracts of vegetation [ 2]. The low- albedo surfaces are now known to be the result of aeolian action on the distribution of sand and dust. The Mariner 4, 6, and 7 spacecraft in 1965 and 1969 stunned the world by showing a cratered, lunar- like martian surface. In 1972, Mariner 9 showed a more Earth- like surface- indeed, there were numerous channels, some carved by massive floods, others perhaps by fluvial run- off or sapping. The Viking orbiters ( 1976- 1980) provided additional images; these formed the basis of study for the past two decades. In the mid- 1980' s some investigators began to speak of Mars as having a more " wet" history than was discussed earlier [ 3,4]. Parker et al. [ 5- 7] showed similarities between landforms along the margins of the great northern plains of Mars and landforms along the margins of Great Basin Lakes Bonneville and Lahontan; this work has stimulated much additional research [ e. g., 8] and controversy [ e. g., 9]. Others began to identify smaller basins that seem to contain sediments deposited by various channels. Among the earliest convincing arguments were presented by De Hon [ 10], who simply noted the occurrence of places where water had ponded along the course of some of the giant martian outflow channels. Evidence Mounts: The most commonly- cited place on Mars that may have been an ancient lake is within a 175 km- diameter crater, Gusev, located at 5° S, 184.5° W. A channel, Ma'adim Vallis, flowed into this crater; and an eroded, delta- like deposit is found at the site where the channel contacts the basin. This particular site has been repeatedly described in recent years as a |
