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J.L. Heldmann (NASA Ames Research Center), O.B. Toon (University of Colorado), W.H. Pollard (McGill University), M.T. Mellon, J. Pitlick (University of Colorado), C.P. McKay (NASA Ames Research Center), D.T. Andersen (SETI)
Geomorphic evidence suggests that recent gullies on Mars were formed by fluvial activity. Irrespective of the ultimate source of the fluid carving the gullies, we seek to understand the behavior of this fluid after it reaches the Martian surface. We numerically simulate the flow of liquid water within gully channels to determine whether liquid water can flow over sufficient distances to carve the observed channels and to place constraints on the flow rate and salinity of the water. This model is first developed to simulate a well-observed terrestrial example of channel flow in the High Canadian Arctic. This model is then applied to Mars.
We find that, contrary to popular belief, the fluvially-carved Martian gullies are consistent with formation conditions such as now occur on Mars, outside of the temperature-pressure stability regime of liquid water. Our model of the action of flowing pure liquid water produces the observed gully length distribution only at surface pressures and temperatures below the triple point where liquid water simultaneously boils and freezes and thus suggests that gullies were formed under conditions similar to present-day Mars. Numerical simulations show that pure liquid water flowing at rates of 15-60 m3/s is consistent with the observations of the gullies. The formation of gullies on Mars is inconsistent with briny fluid flows with significant flow rates because inhibiting rapid evaporation by vapor pressure suppression (or other means such as ice sheets capping the flow, or a higher pressure climate state) results in channels that are much longer than those observed on Mars. Instead, our model indicates that these fluvially-carved gullies formed in the low temperature and low pressure conditions of present day Mars by the action of relatively pure liquid water.
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Bulletin of the American Astronomical Society, 37 #3
© 2004. The American Astronomical Soceity.