Sulfate Martian soil

A cold early climate and a thin CO2 atmosphere are consistent with the ubiquity of primary igneous minerals and the apparent absence of secondary minerals and copious carbonates on the surface. Aqueous eruptions introduced soluble chloride and sulfate salts into Martian soils, leaving clays and carbonates within the crust. If the Martian crust hosts a deep biosphere, aqueous eruptions could bring organisms or their chemical signature to the surface. The biotic component of any recent eruptions may be preserved in transient ice in cold traps on the surface. 

Professor Sam Kounaves and his students at Ihfts University were filled with excitement as their Wet Chemistry Laboratory experiment aboard the Phoenix Mars Lander returned a stream of information about the composition of Martian soil scooped up hy a robotic arm. The arm delivered 1 gram of soil through a sieve into a lieakei fitted with a suite of electrochemical sensors described in Chapter 15. Aqueous solution added to the beaker leached soluble salts from the soil while sensors measured ions appearing in the liquid. Unlike other ions, sulfate was measured hy a precipitation titration with Ba ... 

Sulfate in soil on Mars, A barium sulfate precipitation titration described at the opening of this chapter is shown in the figure. The initial concentration of Cl" before adding BaCl2 was 0.000 19 M in 25 mL of aqueous extract of Martian soil. At the end point, when there is a sudden rise in Ba, [cr] = 0.009 6 M. 

Kounaves SP, Hecht MH, Kapit J et al (2010) Soluble sulfate in the martian soil at the Phoenix landing site. Geophys Res Lett 37 n/a-n/a. doi 10.1029/2010GL042613... 

Although TES and THEMIS are sensitive to carbonates and sulfates, these minerals have not yet been detected unambiguously from orbit (Bandfield, 2002). The low carbon abundance in APXS-analyzed soils rules out much carbonate, although appreciable sulfur and chlorine are present in all soils. Thermodynamic stability considerations suggest that sulfates and iron carbonates should be present under martian conditions (Clark and Van Hart, 1981 Catling, 1999). It is unclear whether sulfate formed by reactions with acidic vapor from volcanic exhalations (Banin et al., 1997) or evaporation of surface brines (Warren, 1998 McSween and Harvey, 1998). 

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