Water Activity of Thin Films in High Latitude Martian Ground Ice: A Preliminary Study
Abstract
Shallowly buried ground ice is nearly ubiquitous on Mars at high latitudes poleward of ~50° in both hemispheres. In the current climate, this ice is perennially cold, i.e., averaging ~190K at ~70° N latitude. Despite low temperatures, thin films of unfrozen water can exist due to interfacial and Gibbs-Thomson premelting at soil-ice interfaces. The presence of salts can further suppress the freezing point. Water activity is a thermodynamic measure of salinity and an indicator of the biological availability of water molecules. We carried out numerical simulations of subsurface temperatures and thin film occurrence over the last 10 Ma of Martian history. We then calculated the water activity in premelted films occurring< 1 m below the surface. In the current climate, peak mid-summer water activity in these films does not exceed 0.6, inconsistent with habitability for known terrestrial organisms. However, obliquity excursions over the past 10 Ma episodically produce mid-summer water activity >0.7, consistent with metabolism in some species of Halobacteriaceae.
- Publication:
-
American Astronomical Society Meeting Abstracts #233
- Pub Date:
- January 2019
- Bibcode:
- 2019AAS...23334603D