Stability and exchange of subsurface ice on Mars

Abstract

[1] We seek a better understanding of the distribution of subsurface ice on Mars, based on the physical processes governing the exchange of vapor between the atmosphere and the subsurface. Ground ice is expected down to $49°latitude and lower latitudes at poleward facing slopes. The diffusivity of the regolith also leads to seasonal accumulation of atmospherically derived frost at latitudes poleward of $30°. The burial depths and zonally averaged boundaries of subsurface ice observed from neutron emission are consistent with model predictions for ground ice in equilibrium with the observed abundance of atmospheric water vapor. Longitudinal variations in ice distribution are due mainly to thermal inertia and are more pronounced in the observations than in the model. These relations support the notion that the ground ice has at least partially adjusted to the atmospheric water vapor content or is atmospherically derived. Changes in albedo can rapidly alter the equilibrium depth to the ice, creating sources or sinks of atmospheric H 2 O while the ground ice is continuously evolving toward a changing equilibrium. At steady state humidity and temperature oscillations, the net flux of vapor is uninhibited by adsorption. The occurrence of temporary frost is characterized by the isosteric enthalpy of adsorption.

The 3–5MHz global reflectivity map of Mars by MARSIS/Mars Express: Implications for the current inventory of subsurface H2O

“…For both hemispheres, the highest values (6 -10) are observed at tropical latitudes. These values are in agreement with laboratory measurements on dry igneous rocks (Campbell and Ulrichs, 1969;Heggy et al, 2007) ice is not stable on the surface, we expect the ground ice to be overlaid by a layer of dry regolith whose thickness depends on latitude, soil physical properties, and the seasonal evolution of surface humidity (Mellon and Jakosky, 1991;Schorghofer and Aharonson, 2005).…”

“…In the case of the southern hemisphere there is a good agreement between the latitude of the ground-ice determined by MARSIS and GRS, with an average latitude of 48-50°, almost constant with regard to longitude. This ground-ice extent is also in good agreement with the calculated stability limit for the currently observed atmospheric conditions (Mellon and Jakosky, 1991;Schorghofer and Aharonson, 2005). This suggests that the icy layer is in equilibrium with the current climatology.…”

The Modern Near-Surface Martian Climate: A Review of In-situ Meteorological Data from Viking to Curiosity

“…At equatorial and low latitudes, brine formation by the melting of ice is unlikely because water ice is not thermodynamically stable in the shallow subsurface at these latitudes (Mellon and Jakosky 1993; Mellon et al 2004;Schorghofer and Aharonson 2005). Similarly, brine formation by deliquescence is less likely to occur in these regions than at higher latitudes.…”

“…In the polar regions, brine formation by the melting of ice in contact with salts is plausible because frost or snow are seasonally deposited on saline soils (Whiteway et al 2009;Martínez et al 2012), water ice is seasonally present in the shallow subsurface (Paige 1992;Mellon and Jakosky 1993;Schorghofer and Aharonson 2005;Cull et al 2010), and temperatures exceed the eutectic value of salts detected on Mars during a significant fraction of the sol (from minutes to hours depending on the location and time of the year) (Möhlmann 2011;Nuding et al 2014;. Moreover, numerical modeling and laboratory experiments indicate that brine formation by deliquescence in the polar region is theoretically possible because simulated diurnal cycles of RH and temperature at the ground at the PHX site are compatible with deliquescence of Ca(ClO 4 ) 2 and Mg(ClO 4 ) 2 salts (Möhlmann 2011;Nuding et al 2014;Nikolakakos and Whiteway 2015).…”

Small-scale trench in the north polar region of Mars: Evolution of surface frost and ground ice concentration

“…Theoretical simulations performed by many authors (Leighton and Murray, 1966;Fanale et al, 1986;Mellon and Jakosky, 1995;Schorghofer and Aharonson, 2005;Aharonson and Schorghofer, 2006) led finally to the conclusion, that the subsurface ice may be present in wide range of latitudes. The neutron and gamma ray spectrometers on board Mars Odyssey spacecraft confirmed, that some subsurface ice is present almost everywhere on Mars except low latitudes (Boynton et al, 2002;Mitrofanov et al, 2004).…”