Tuesday, April 05, 2016

Possible water lubricated grain movement in the circumpolar region of Mars

Possible water lubricated grain movement in the circumpolar region of Mars


Kereszturi et al


In this work we evaluate a new model on the possibility, could microscopic liquid water supported grain movement on Mars happen at the circumpolar region (in Richardson crater) today, combined with the analysis of new HiRISE ESP images. We confirmed earlier (PSP images based) findings on the morphology, sequential growth and two separate phased formation method of flow features emanate from Dark Dune Spots (1: gas-jet driven streaks toward different directions, 2: flow-like streaks downward). We also identified that the gas-jet ejected and back fallen grains surrounded by water ice produce local enrichment of H2O, forming local water ice layer.

Several model scenarios were developed and evaluated to exploit the possibilities of liquid supported flow, including the increased thickness of interfacial liquid layer by salts and impurities, the collapse and movement of loose stratum of air-fallen dust-salt mixture with interbedded liquid layers, the mechanical force to kick-off the movement by hydration/dehydration cycles, and the migrating phase change plus the seeping of thin liquid film around interconnected grains. Selecting the most relevant elements among them, which are also compatible to our current knowledge of Mars, a comprehensive model was built that could be tested. This best model contains four interconnected and subsequent elements: 1. deposition of airfall dust in autumn and winter producing a loose surface layer, 2. spatial concentration of H2O ice by gas-jet activity during the CO2 sublimation phase, 3. mechanical kick-off by daily expansion/contraction cycles to mix the components, 4. engulfed hygroscopic salts and dust grains to enlarge the ratio of liquid to support the flow. The emerged self-amplifying process could produce daily movement in theory. The scenario contains realistic elements; it is in agreement with the observations, and also being testable by laboratory modelling. The analyzed locations are important because of the joint occurrence of concentrated water ice, elevated temperature and moving flow-features; and it also provides insight into the possible current action of liquid water on Mars.

No comments: