In situ analysis of ice table depth variations in the vicinity of small rocks at the Phoenix landing site

Abstract

Prior to the Phoenix mission, ice stability simulations predicted that surface rocks at the landing site would produce depressions in the ice table (the boundary between dry and ice-cemented soil) if ground ice at the site were in diffusive equilibrium with atmospheric water vapor. We use stereo images and digital elevation models to investigate variations in the depth of the ice table near two decimeter-scale rocks at the Phoenix landing site and compare the observed depth variations to ice stability simulations. We find that ice table depth variations observed near rocks at the landing site are consistent with our theoretical predictions. Based on our results we conclude that: 1) Water transport in the near-surface regolith occurs primarily via vapor diffusion; 2) Environmental conditions in which water transport is dominated by diffusion have been persistent at the landing site for 100s to 1000s of years or longer; that is, ground ice is in diffusive equilibrium with atmospheric water vapor; and 3) In diffusive equilibrium, thermal stability dictates the depth of the ice table on horizontal length scales as small as centimeters. Copyright 2010 by the American Geophysical Union.