Theory of ground ice stability in sublimation environments

Permanently stable ground ice is found beneath a permanently frost free surface on Mars, and similar conditions exist in the Antarctic Dry Valleys. This phenomenon is due to a balance of the vapor pressure of the ice with the atmospheric humidity in the presence of large amplitude temperature oscillations. An exactly solvable model example shows that the fraction of time the atmosphere needs to be saturated to stabilize the ice decreases with temperature amplitude. It is estimated that for conditions that prevail on Mars today, the mean temperature needs to be about 5 K lower than the frost point temperature for ground ice to be stable. A decomposition method to evaluate the contribution of short term weather events to ground ice stability is developed; when applied to a study site in the Dry Valleys, it reveals that the coldest periods contribute most to stabilization.