Numerical modeling of a desiccation mechanism for formation of Crater Floor Polygons on Mars

Details Numerical modeling of a desiccation mechanism for formation of Crater Floor Polygons on Mars Numerical modeling of a desiccation mechanism for formation of Crater Floor Polygons on Mars

Dec 2010

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2010agufm.p53c1534e&link_type=abstract

American Geophysical Union, Fall Meeting 2010, abstract #P53C-1534

Biology

[1800] Hydrology, [5220] Planetary Sciences: Astrobiology / Hydrothermal Systems And Weathering On Other Planets, [5419] Planetary Sciences: Solid Surface Planets / Hydrology And Fluvial Processes

Scientific paper

Crater floor polygons (CFPs) are polygonal networks that are located in many impact crater floors on Mars (El Maarry et al., 2010). They have been mapped using high resolution images and were shown to display diameters ranging from 15 to 350 meters. Morphological investigations, aerographic distribution, and analytical modeling lend support to a desiccation mechanism for these polygons as opposed to seasonal thermal contraction processes (El Maarry et al., 2010). This would imply the past existence of lakes or volatile rich sediments in the crater basins as a result of an impact-generated hydrothermal system. However, a desiccation pathway is yet to be formulated to explain the development of these structures under past and current Martian conditions. We devised a hydro-elastic model to describe the stress-strain conditions in a soil undergoing desiccation under Martian conditions. Our results show that given enough desiccation, stresses build up to values that lead to formation and propagation of cracks. In addition, assuming that the time frame for formation of the Martian desiccation polygons is comparable to the one for the terrestrial analogs, we can put some constrains on the physical properties of the soil involved. Finally, we propose a mechanism for formation of desiccation polygons on Mars (Fig.1). Reference: El Maarry M. R., Markiewicz W.J., Mellon M., Goetz W., Dohm J., and Pack A., (2010). Crater Floor Polygons : Desiccation Patterns of Ancient Lakes on Mars?. J. Geophys. Res., doi:10.1029/2010JE003609, in press Fig.1. Proposed formation pathway for CFPs. A: A lake (dashed lines) lies above a saturated zone. A thin ice layer (grey zone) may form on top (assuming current Mars climate) . B: As the lake dries/sublimates away, a dried-up zone forms in the middle as water is either draining downwards or vapor is rising (for example, through thermal vapor diffusion) to thicken the ice layer on top. Fractures initiate at the boundary between the ice and the dried zone. C: Thermal contraction processes eventually lead to cracking of the upper frozen soil layer preferably above the fractured weakened zones thus exposing the fractures. D: Further thermal cycles may form the secondary thermal contraction features within the larger polygons.

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