Vortrag > Autor > Dokumentname > Folie 1 EMC/ERH-properties of thin layers of martian analogue soils – First results A. Lorek German Aerospace Center (DLR) / Fax: / Phone: )

Vortrag > Autor > Dokumentname > Folie 2 Motivation [Rivkina et al., 2000] has shown that live its possible below 0°C and at low liquid water contends ( > 2 mono layer of water -- 1 mono layer = 0,3nm thickness) Chemical experiments at DLR have shown that the Photo-Fenton-Reaction is possible at low water contents (corresponding to a few - n > 2 – mono layers). Liquid water influences physical properties of soils Rheology Electric- and heat conductivity Dielectric and related spectral properties The water content of soils significantly influences their chemical, physical and biological properties. gullies in a crater wall (at 168.2°W, 37.4°S) (MOC M ) Photo NASA

Vortrag > Autor > Dokumentname > Folie 3 Mars analogue soil Bentonite (Clay with a high content of montmorillonite) Montmorillonite was detected on the basis of spectrometer data from Mars Express [Poulet et al., 2005] Is distinguished as a promising habitat for earlier or current live [Chevrier; Mathe, 2006] specific surface 50,3 m²/g, absolute density 2,38 g/cm³ (Federal Institute for Materials Research and Testing (BAM)) JSC MARS-1 (Volcanic material from Mauna Kea Vulcan (Hawaii)) Its spectra is like the Olympus-Amazonis Region of Mars [Allen et al., 1998] Specific surface 146 m²/g, absolute density 2,64 g/cm³ (BAM) The upper millimeter of the martian surface is of particular interest It interacts directly with the diurnally varying atmospheric humidity, which can reach saturation during the night and early morning hours Adsorption/desorption of water in the soil and freezing of water can be a consequence Could contain several mono layers of liquid water

Vortrag > Autor > Dokumentname > Folie 4 EMC/ERH Water content in the upper soil layers depends on the relative humidity of the atmosphere Equilibrium relative humidity (ERH) is related to an equilibrium moisture content (EMC) An increase of relative humidity leads to an increase of the soil moisture content The properties of the soil (structure, specific surface, free charges, van der Waals-forces) determine the EMC saturation vapor pressure p 0 [Pa] water activity [a w ] Equilibrium relative humidity Desorption isotherms [BAM] Equilibrium moisture content

Vortrag > Autor > Dokumentname > Folie 5 Theory of the liquid water content in soils (Möhlmann`s formula) Möhlmanns formula establish a relationship between ERH and adsorbed (liquid) water content Theory (Möhlmann) based on Hamaker-Theory of van der Waals interactions (planar surfaces) in combination with the saturation water vapor formula Hamaker- constant ( J to J ), specific surface and r.h. must be known

Vortrag > Autor > Dokumentname > Folie 6 Atmospheric humidity and soil moisture on Mars It is expected that the water content in upper soil is in a range from 2 to 10%wt in mid- and low latitudes Relative humidity ranges between 100 %r.h. in night - and early morning hours and near 0%r.h. about noon During 100% r.h. the first millimeter can adsorb a lot of mono layers water Atmospheric humidity at mid- and low latitudes is in the range of - 80° to -100°C T d (0,12Pa to 0,004 Pa) There is only a weak increase of soil moisture with decreasing temperature Sorption isotherm at 20°C corresponds nearly to an isotherm at lower temperatures Viking 2 at 47.97° N and ° W (Foto NASA 18 Mai 1979) Feldman, Los Alamos National Laboratory, 2003 Desorption isothermes of Montmorillonite at -16°C, 2°C, 20°C u. 30°C based on data from Jähnchen, Bish, Möhlmann, Stach Investigation of the water sorption properties of Mars-relevant micro- and mesoporous minerals, Icarus, 2006

Vortrag > Autor > Dokumentname > Folie 7 Dielectric test plate capacitor (10 Hz - 1MHz) Measurement system for detection of liquid water content in soils Distance between capacitor plates is 1,27mm (0.82mm soil, 0.45mm air gap) Gas in- and output Possible to evacuate the capacitor Maximum gas flow through the capacitor is 15 NL/h Soil adsorb/desorb water from gas flow Water significantly influence the DK of soil If formation of ice occurs, the DK decreases to 3,25 at frequencies about 100KHz

Vortrag > Autor > Dokumentname > Folie 8 Soil moisture measurement at JSC Mars 1 Measurements at 25°C and 1013 hPa for frequencies (10Hz, 90Hz, 1KHz, 5KHz, 10KHz, 100 KHz and 1MHz) Soil probes were baked out at 105°C over 24h Results Considerable and repeatable dependence of the DK on soil moisture content 3,8 %wt correspond to approximately 1 mono layer of water 10 Hz 90 Hz 1 KHz 5 KHz 10 KHz 100 KHz 1 MHz

Vortrag > Autor > Dokumentname > Folie 9 Liquid water content in JSC Mars 1 and Bentonite in a temperature range from +25°C to -70°C JSC Mars 1 shows indication of freezing at -35°C (9,4 %wt curve) 7,6 %wt curve (close of the 9,4 %wt curve) indicates that, down to -35°C, 2 mono layers are liquid 6 %wt curve shows no indication of freezing approximately 1,5 mono layers are liquid down to -70°C 9,4%wt curve for Bentonite shows indication of freezing at -15°C 7,8%wt curve has a nearly linear decrease over the full temperature range: No freezing is observable 4,8 %wt curve shows the same behavior: Approximately 3 mono layers are in the liquid state down to -70°C

Vortrag > Autor > Dokumentname > Folie 10 Diurnal temperature variation (-70°C to +5°C), Gas flow 15Nl/h (air), constant humidity of -80°C T d, pressure1013 hPa, Time period 28 days (Equilibrium not yet reached) Result 2,8 %wt soil moisture content at the end of the measurement (0.75 mono layer)

Vortrag > Autor > Dokumentname > Folie 11 Conclusions Measurements (under normal pressure at JSC Mars 1) show that adsorbed water in the simulated martian soils is present with contents not less than 3%wt (1 mono layer) First Measurements lead to the assumption (JSC Mars 1) that, down to -35°C, more than 2 mono layers (8 %wt) are in a liquid state and more than 1 mono layer is liquid at -70°C A liquid water content of 2 mono layer at -35°C would corresponds to a Hamaker-constant of 3,5x J (Möhlmanns - formula) Chemical reactions and live processes can be supported by liquid water below 0°C Future prospects Further measurements under normal pressure and at temperatures below 0°C Measurements under martian conditions (CO 2 atmosphere, 600 Pa) Use of a dielectric measurement system (TDR) to confirm and to extend the given results