Martian regolith

Plumb, R. C., Tantayanon, R., Libby, M., and Xu, W. W. (1989). Chemical model for Viking biology experiments Implications for the composition of the martian regolith. Nature (London) 338, 633-635. 

Earlier, we examined the movement of salts through a Martian regolith under a freezing regime (Fig. 5.18). Initially, each layer (0.5km) was separately equilibrated this initial step removed virtually all the Fe(II) as siderite, most of the Ca as calcite, and a lesser percent of Mg as hydromagnesite. In a second step, we froze the system from the top down, which led to salt exclusion, increasing salt concentrations with depth, and additional precipitation of calcite and hydromagnesite (Fig. 5.18). 

Farquhar J., Savarino J., Jackson T. L., and Thiemens M. H. (2000) Evidence of atmospheric sulphur in the martian regolith from sulphur isotopes in meteorites. Nature 404, 50-52. 

McSween H. Y. and Keil K. (2000) Mixing relationships in the martian regolith and the composition of globally homogeneous dust. Geochim. Cosmochim. Acta 64, 2155-2166. 

On May 25, 2008, the mission landed and began to investigate samples. The mass spectrometer obtained spectra of atmospheric constituents, and measured the evolved gas from multiple samples collected directly in front of the lander [82,83]. It was critical in the potential discovery of calcium carbonate in surface material when it was used in peak mode to identify when CO2 was evolved. A significant increase in the concentration of CO2 was detected from a sample named Wicked Witch when the oven temperature approached 1200°C [82]. In the discovery of perchlorate in the Martian regolith, TEGA identified the evolved mass from O2 in a sample named Baby Bear. The onset of evolved O2 at 325°C and a peak at 465°C, which is consistent with the thermal decomposition of perchlorate [84]. These two discoveries, along with the measurement of the Ph and identification of precipitation from water ice clouds were highlights of the Phoenix mission [85]. 

Lukow SR, Kounaves SP (2005) Analysis of simulated Martian regolith using an array of ion selective electrodes. Electroanalysis 17 1441-1449... 

Fig. 6.3 (a) Potential vs. time traces recorded for the ISEs for the Sol-30 (Rosy Red) sample on Mars. The two vertical lines indicate the addition of the calibrant crucible and the sample, (b) Concentrations of cations and anions in solution containing 25 niL leaching solution and 1 g of martian regolith for three of the WCL units. Reprinted with permission from reference (12)... 

The pH of the martian regolith was measured using two polymer-based membrane ISEs and an iridium oxide electrode. Measurement of pH of the martian regolith was seen as a critical objective for the mission, which is why this measurement was performed in triplicate. The dynamic range of the polymer-based pH ISEs as determined preflight was 1 < pH <9, while the dynamic range of the iridium... 

The NERNST concept applies several lessons learned from the Phoenix mission in order to provide a more robust, sensitive, and accurate measurement of the martian regolith. With NERNST, a sample of martian soil is first mixed with water off-chip in a sample extraction hub, and then the sample leachate (the water separated from the soil-water mix) is pumped on-chip for analysis. The sample can then be manipulated (with acid/base, BaCl2, etc.) and measured multiple times with multiple electrodes in order to provide a deeper understanding of the soluble chemistry of the soil sample. 

Fig. 5.18. The regolith layer (0.5 km) molal concentrations as the freezing front moves through the Martian profile. Minerals that should theoretically precipitate within the profiles either from the initial evaporative concentration or later from freezing concentration are listed...

Numerous authors (e.g., Warren, 1994 Wieler, 2002 Nyquist et al., 2001) have contrasted the exposure histories and other properties of lunar and martian meteorites. On average, we would expect key systematic differences to relate to their respective distances from the Earth (or more precisely how easily their ejecta could attain Earth-crossing orbits), the respective depths of their gravitational wells, the mechanical properties of their regoliths, and the relative fluxes of impacting bodies. 

Mars is characterized by low noble gas abundances in the atmosphere, with equivalent total planet concentrations that are 10 times less than on Earth. The amount of martian carbon is also not well known while the atmosphere has only 7 X 10 g C, equivalent to 0.01 ppm for the bulk planet (Owen et al, 1977), a large fraction may be stored in the polar regolith. 

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