A perchlorate brine lubricated deformable bed facilitating flow of the north polar cap of Mars: Possible mechanism for water table recharging

摘要

The Phoenix Wet Chemistry Lab (WCL) discovered substantial amounts of magnesium, calcium, and sodium perchlorate in the soil of polar Mars. Magnesium perchlorate is likely the dominant salt in the polar region's soils. But it could be that the cations are contributed by a mixture of Mg, Ca, and Na. Mg, Ca, and Na perchlorate brines can stay liquid as low as ～–74, –32℃, respectively. WCL reports 0.7 % (wt) of the soil is pure perchlorate, and if 5% of the northern permanent ice cap is soil, then the perchlorate could make about 1/2800 of the ice cap. This suggests there could be enough perchlorate in the ice cap to generate about 1-3 m of brine at the bed. Large areas under the north polar cap have basal temperatures above –69℃ so the Mg and Ca perchlorate brines would be liquid. Because of its high density, the perchlorate brine would pool over impervious layers and make the bed into a perchlorate sludge, which could be mobilized and deformed by the weight of the overburden of ice and soil. The sludge would be deformed and moved outward and stop where the basal temperature dropped below –69℃. During the warmest climates, any frozen cold dam at the edge could be breached and the brine reintroduced to the polar surface. Some of the brine could have penetrated downward under the ice cap. This mobile sludge-bed ice cap has been modeled with a 2-D time-varying model. Results of such model runs have similarities to measured layers found by shallow subsurface radar.