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Water vapor diffusion in Mars subsurface environments

Hudson, Troy L. and Aharonson, Oded and Schorghofer, Norbert and Farmer, Crofton B. and Hecht, Michael H. and Bridges, Nathan T. (2007) Water vapor diffusion in Mars subsurface environments. Journal of Geophysical Research E, 112 . Art. No. E05016. ISSN 0148-0227. doi:10.1029/2006JE002815.

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The diffusion coefficient of water vapor in unconsolidated porous media is measured for various soil simulants at Mars-like pressures and subzero temperatures. An experimental chamber which simultaneously reproduces a low-pressure, low-temperature, and low-humidity environment is used to monitor water flux from an ice source through a porous diffusion barrier. Experiments are performed on four types of simulants: 40–70 µm glass beads, sintered glass filter disks, 1–3 µm dust (both loose and packed), and JSC Mars–1. A theoretical framework is presented that applies to environments that are not necessarily isothermal or isobaric. For most of our samples, we find diffusion coefficients in the range of 2.8 to 5.4 cm^2 s^-1 at 600 Pascal and 260 K. This range becomes 1.9–4.7 cm^2 s^-1 when extrapolated to a Mars-like temperature of 200 K. Our preferred value for JSC Mars–1 at 600 Pa and 200 K is 3.7 ± 0.5 cm^2 s^-1. The tortuosities of the glass beads is about 1.8. Packed dust displays a lower mean diffusion coefficient of 0.38 ± 0.26 cm^2 s^-1, which can be attributed to transition to the Knudsen regime where molecular collisions with the pore walls dominate. Values for the diffusion coefficient and the variation of the diffusion coefficient with pressure are well matched by existing models. The survival of shallow subsurface ice on Mars and the providence of diffusion barriers are considered in light of these measurements.

Item Type:Article
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Aharonson, Oded0000-0001-9930-2495
Bridges, Nathan T.0000-0002-6790-6793
Additional Information:© 2007 American Geophysical Union. Received 18 August 2006; revised 29 November 2006; accepted 1 February 2007; published 31 May 2007. We wish to thank Matt Siegler for his work on initial chamber development, and Steve Clifford and Bill Boynton for their helpful reviews. Early work was carried out at the Extraterrestrial Materials Simulation Laboratory (EMSiL) at JPL with the help of Jackie Green, Stephen Fuerstenau, and Greg Peters. This work was funded in part by the JPL Director’s Discretionary Fund and by NASA’s Mars Fundamental Research Program.
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JPL Director’s Discretionary FundUNSPECIFIED
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ID Code:13577
Deposited By: Tony Diaz
Deposited On:08 May 2009 18:21
Last Modified:08 Nov 2021 22:39

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