Escape of Martian Water: Modeling the Atmosphere from the Surface to the Exobase
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چکیده
Water has had a major impact on the martian surface and climate, and understanding the history of water is a major scientific goal of NASA's Mars Exploration Program. While there is ample and increasing evidence that the ancient Mars had copious amounts of water on its surface, there is no general understanding of how much of that water remains sequestered in the martian crust today, and how much may have escaped to space over time. While several groups have modeled the escape processes from the upper martian atmosphere, water molecules must be dissociated in the lower atmosphere, and the diffusion of their byproducts from the surface to the exobase (where they can escape into space) is subject to many factors. We here propose an extension of previous observational and modeling programs related to the martian atmosphere to develop a model which will include all of the key elements of the escape of martian water from the surface into space. We will adapt an existing finite-element simulation code, presently used to model the martian ionosphere, to extend down to the surface. This will treat the dissociation of water, including the varying rates of photo-induced and condensation-induced fractionation of deuterated species, their diffusion into the upper atmosphere, their chemistry (lower atmosphere) and photochemistry (upper atmosphere), and their energy-dependent escape from the exobase. Armed with a physics-based model of the entire atmosphere, it will then be possible to simulate conditions in the history of Mars, and determine the rates and main factors which have controlled the escape of martian water.
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تاریخ انتشار 2004