Susan E. Postawko

Carbon dioxide: Adsorption on palagonite and partitioning in the Martian regolith

Abstract We report new CO 2 adsorption measurements on palagonites. These results are used together with earlier results on basalt and nontronite adsorption to derive a “generic” relationship which is valid to within a factor of 3 for likely mixtures of basalt and weathering products of basalt. The relationship involves only t, P CO 2 , and the specific surface area, and is relatively insensitive to mineralogy. It is used to predict the distribution and exchange of CO 2 on Mars. We conclude: (1) One to two orders of magnitude more CO 2 is adsorbed on the regolith than is present in the atmosphere and cap. (2) Nonetheless, most of the initially degassed CO 2 must have been lost to space or must be present as carbonates, especially if there was enough degassed CO 2 to provide a significant early greenhouse effect. (3) Given the derived relationship, the CO 2 vapor pressure curve, and the constraint that the system exhibits the current P CO 2 at the current obliquity, it is possible to predict approximately the atmospheric pressure at any obliquity (with or without a cap) without knowing the total available CO 2 inventory, the regolith mass, the regolith distribution, or its mineralogy, any better than those parameters are currently known.

Changes in erosional style on early Mars - External versus internal influences

The conditions which led to the formation of the valley networks on Mars were apparently very different from present-day conditions. In this paper we investigate the relative importance of higher early surface temperatures versus higher deep regolith temperatures in producing a shallower depth to liquid water in the regolith on Mars. If enough CO2 is in the atmosphere, the surface temperature could be raised to near the freezing point around 3.8 b.y. ago despite a possibly weak early sun, at least in the equatorial regions. On the other hand, it has been argued that higher internal regolith temperatures, associated with a much higher heat flow around 3.8 b.y. ago than at present, could reduce the depth to liquid water sufficiently to account for the change in erosional style with time. In fact, it does not make sense on physical grounds to consider these two mechanisms separately. The effectiveness of both of these mechanisms is dependent on a high early heat flow. In general, we find that if early heat flow were around 100 mW m−2, then the total available CO2 in the atmosphere-plus-regolith system becomes critical. If total available CO2 were greater than about 4 bars, then the atmospheric greenhouse effect could play an important role in raising the liquid water level closer to the surface, but only in equatorial regions. On a global basis, condensation of large amounts of atmospheric CO2 may inhibit surface warming. If the total CO2 were 1 bar or less, the atmospheric greenhouse effect raises the surface temperature by only a few degrees. Heat flows greater than 100 mW m−2 can still raise the liquid water level from over 1 km to less than 350 m, enabling substantially more efficient network formation very early in martian history.

Mars: Long Term Changes in the State and Distribution Of H2O

A model for H2O distribution and migration on Mars has been formulated which takes into account: 1) thermal variations at all depths in the regolith due to variations in obliquity, eccentricity and the solar constant; 2) variations in atmospheric partial pressure of water (PH2O) caused by corresponding changes in polar surface insolation; and 3) the finite kinetics of H2O migration in both the regolith and atmosphere. Results suggest that regolith H2O transport rates are more strongly influenced by polar-controlled atmospheric PH2O variations than variations in pore gas PH2O brought about by thermal variations at the buried ice interface. The configuration of the ice interface as a function of assumed soil parameters and time is derived. Withdrawal of ice proceeds to various depths at latitudes 50° and transfer of H2O to the polar cap. The transfer has a somewhat oscillatory character, but only 1g/cm2 is shifted into and out of the regolith during each obliquity cycle. The net irreversible and inexorable transfer of H2O to higher latitudes involves between 1 × 106 km and 1 × 107 km3 of H2O over the history of Mars for most reasonable sets of assumptions. This mass is comparable to the amount of material removed from deflated terrain at mid and low latitudes and to the mass of the polar cap. We conclude that this process combined with periodic thermal cycles played a major role in development of the fretted terrain, deflationary features in general, patterned ground, the north polar cap and the layered terrain.