Water vapor diffusion in Mars subsurface environments

Abstract

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 cm2 s−1 at 600 Pascal and 260 K. This range becomes 1.9–4.7 cm2 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 cm2 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 cm2 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.

Modeling vapor diffusion within cold and dry supraglacial tills of Antarctica: Implications for the preservation of ancient ice

“…Other forces influence vapor transport, including osmotic pressure and nonisothermal vapor flux; but it has been reported that Fickian diffusion processes dominate transport in extreme cold environments (Chevrier et al, 2007(Chevrier et al, , 2008Hudson et al, 2007). Our vapor-diffusion model ignores the very minor effects of Knudsen diffusion and does not specifically track vapor density beyond saturation (as may occur with the formation of hoar frost).…”

Experimental study of the sublimation of ice through an unconsolidated clay layer: Implications for the stability of ice on Mars and the possible diurnal variations in atmospheric water

“…From 2 to 75 mm, the sublimation rate should decrease by a factor ∼38 (see Section 4.1), while the temperature difference generates an Fig. 2), as a function of surface temperature for a variety of clay depths, L. The data lie below the theoretical (Ingersoll, 1970) and experimental (Moore and Sears, 2006) curve for water ice sublimation. Sublimation rate decreases with regolith thickness.…”

The martian soil as a planetary gas pump

“…Mars is known to have buried ice within its subsurface 20 and water vapour can be transported by diffusion to the surface 12 . Ref.…”