Abstract
We have measured the salt content changes of soil samples in laboratory
experiments to simulate the salt and water migration that may cause
duricrust formation on Mars. Although the cold, dry surface of modern
Mars lacks abundant, liquid water, salts may stabilize scant liquid
water as thin films through freezing point depression, allowing them to
migrate along temperature and water concentration gradients driven by
evaporation at the surface, and to transport salts where they
precipitate and cement loose soil grains into crusts. Our work also
demonstrates that spectral data complements salt content changes we
measured, by showing changes in the hydration states inferred in the
1950 nm water band. We simulated salt and water migration, required in
salt crust formation, in Mars analog regolith, through desiccating wet
loess doped with either MgCl2, MgSO4, or
CaSO4 at a temperature range of -196 °C to 150 °C. Our
experiments allowed exploring temperature and depth dependencies on
water and salt behaviors in 2 cm tall cylindrical soil sample tubes. The
1000 nm to 2400 nm spectral slope and the area of the 1950 nm water band
correlate with salt concentration. MgSO4 exhibits the
greatest migration, CaSO4 hydrates with weak migration,
and MgCl2 migrates with moderate hydration. Spectral
analysis may be useful in estimating salt and water migration, and in
turn, aiding in interpreting hydrological and climatic history of the
regolith of Mars.