Jochen Jänchen

Hygroscopic Salts and the Potential for Life on Mars

Hygroscopic salts have been detected in soils in the northern latitudes of Mars, and widespread chloride-bearing evaporitic deposits have been detected in the southern highlands. The deliquescence of hygroscopic minerals such as chloride salts could provide a local and transient source of liquid water that would be available for microorganisms on the surface. This is known to occur in the Atacama Desert, where massive halite evaporites have become a habitat for photosynthetic and heterotrophic microorganisms that take advantage of the deliquescence of the salt at certain relative humidity (RH) levels. We modeled the climate conditions (RH and temperature) in a region on Mars with chloride-bearing evaporites, and modeled the evolution of the water activity (a(w)) of the deliquescence solutions of three possible chloride salts (sodium chloride, calcium chloride, and magnesium chloride) as a function of temperature. We also studied the water absorption properties of the same salts as a function of RH. Our climate model results show that the RH in the region with chloride-bearing deposits on Mars often reaches the deliquescence points of all three salts, and the temperature reaches levels above their eutectic points seasonally, in the course of a martian year. The a(w) of the deliquescence solutions increases with decreasing temperature due mainly to the precipitation of unstable phases, which removes ions from the solution. The deliquescence of sodium chloride results in transient solutions with a(w) compatible with growth of terrestrial microorganisms down to 252 K, whereas for calcium chloride and magnesium chloride it results in solutions with a(w) below the known limits for growth at all temperatures. However, taking the limits of a(w) used to define special regions on Mars, the deliquescence of calcium chloride deposits would allow for the propagation of terrestrial microorganisms at temperatures between 265 and 253 K, and for metabolic activity (no growth) at temperatures between 253 and 233 K.

Relationship between acid-strength and framework aluminum content in dealuminated mordenites

Abstract Calorimetric measurements of ammonia at 423 K on dealuminated mordenites with Si/Al ratios between 7 and 48 show a distinct dependence of the number of very strong acid sites on the content of the framework aluminum. Plots of these numbers against the molar fraction of aluminum yield a volcano-shaped curve with an abscissa of 0.096, which corresponds to a calculated value of Barthomeuf, thus verifying her theoretical concept. Calorimetric measurements of Klyachko et al. are in good coincidence with the given data.

Water sorption in faujasite- and chabazite type zeolites of varying lattice composition for heat storage applications

Abstract The water sorption properties of faujasite type zeolites with different Si/Al ratios as well as of natural chabazite and two different SAPO-34 molecular sieves have been investigated systematically by thermogravimetry (TG), differential scanning calorimetry (DSC), microcalorimetry, and isotherm measurements. Via changing the lattice chemistry of the zeolites by dealumination and isomorphous substitution of T atoms the energetics of the water sorption have been tailored. According to this approach the charging and discharging properties of microporous molecular sieves in a thermochemical storage process can be controlled as has been demonstrated in a lab-scaled storage of 1.5 L volume.

Water and carbon dioxide sorption properties of natural zeolites and clay minerals at martian surface temperature and pressure conditions

Abstract The verified presence of smectites, natural zeolites, sulfates and other water-bearing minerals on the martian surface have encouraged us to study their water and CO 2 adsorption behaviour under conditions close to martian equatorial surface temperature and pressure. The results for smectites and zeolites show about 2.5-25 wt% of (partially mobile) water at low temperatures and a very low partial pressure of 0.001 mbar. Mars relevant minerals such as nontronite, montmorillonite, clinoptilolite and chabazite can adsorb water even in a more than thousand-fold surplus (6 mbar) of carbon dioxide. The presence of water in equatorial latitudes might be of importance for water involved chemistry and hypothetical exobiological activity on Mars.