A process to make massive ice in the martian regolith using long-term diffusion and thermal cracking

This paper describes a simple standard model of water transport through regolith that includes diffusive migration and phase changes driven by damped seasonal temperature waves. A hitherto unused first-order process is then added, that can produce ice densities much greater than those allowed by the initial dry porosity. Voids are produced in cooling icy regolith when tensile stresses exceed the cracking threshold (similar to 2 MPa). These stresses build up through all interaction of thermal contraction and elastic-plastic response. When the cracks open Lip after tensile failure there is purely thermal void enhancement and Subsequent reduction as the regolith warms again. When the cracks are open the porosity is increased and they partially fill with ice crystals. Thus the void reduction oil warming cannot go back to the original zero point and the bulk density office is increased with each temperature cycle. The cracking and thermal adjustment happen at scales of meters to millimeters. The large cracks can Occur in pure ice and/or homogeneous icy material and the smaller cracks are produced by rock cobbles, pebbles, and grains having a much smaller coefficient of thermal expansion than ice. Thus a hierarchy of cracks and voids forms each temperature cycle and augments the ice content. The process can take the upper few meters of a pore-saturated icy soil from 28% by mass ice content to 70% in 10 Ma. This mechanism and the seasonal temperature cycle can plausibly produce massive ice deposits in the upper few meters of Mars' high-latitude regolith by diffusion and also keep the massive-ice regolith effectively Porous to water vapor transport. The obliquity Cycle Call produce tensile stresses nearing 2 MPa down to similar to 100 m depth so even deeper cracking could be happening. Crown Copyright (c) 2005 Published by Elsevier Inc. All rights reserved.