Soluble sulfate in the martian soil at the Phoenix landing site

Abstract

Sulfur has been detected by X‐ray spectroscopy in martian soils at the Viking, Pathfinder, Opportunity and Spirit landing sites. Sulfates have been identified by OMEGA and CRISM in Valles Marineris and by the spectrometers on the MER rovers at Meridiani and Gusev. The ubiquitous presence of sulfur has been interpreted as a widely distributed sulfate mineralogy. One goal of the Wet Chemistry Laboratory (WCL) on NASA's Phoenix Mars Lander was to determine soluble sulfate in the martian soil. We report here the first in‐situ measurement of soluble sulfate equivalent to ∼1.3(±0.5) wt% as SO4 in the soil. The results and models reveal SO42− predominately as MgSO4 with some CaSO4. If the soil had been wet in the past, epsomite and gypsum would be formed from evaporation. The WCL‐derived salt composition indicates that if the soil at the Phoenix site were to form an aqueous solution by natural means, the water activity for a dilution of greater than ∼0.015 g H2O/g soil would be in the habitable range of known terrestrial halophilic microbes.

Geochemistry of Carbonates on Mars: Implications for Climate History and Nature of Aqueous Environments

“…8) ). In addition, the soil pH (7.7 ± 0.3), [Ca 2+ ], and [Mg 2+ ] measured by the WCL instrument is consistent with the presence of carbonate minerals in the soil (Kounaves et al 2010b). TEGA also detected a release of CO 2 at a low temperature (between 400°and 680°C) that has been interpreted to be due to either Fe, Mg .…”

The geology of Australian Mars analogue sites

“…The system was proposed as a possible Mars analogue by Benison et al (2007a, b) although the waters are not as concentrated and at higher pHs than those observed in Western Australia (Bowen and Benison, 2009). While it is unreasonable to expect martian surface environments to be strongly acidic everywhere, as shown by the recent results from the Phoenix lander where the soil pH is 8:370:5 (Kounaves et al, 2009), such moderate to slightly acidic saline environments such as Lake Tyrrell may still be applicable as analogues to many ancient martian environments. The weakly acidic lakes and boinka complexes of the Eyre Peninsula (Kimber et al, 2002) may also have Mars analogue potential, but further work is required to assess their value.…”

The Potential for Biologically Catalyzed Anaerobic Methane Oxidation on Ancient Mars

“…Sulfur-bearing species have been identified at several surface sites (Toulmin et al, 1977;Wänke et al, 2001;Squyres et al, 2004;Wang et al, 2006;Kounaves et al, 2010). Various regionally extensive polyhydrated and monohydrated sulfate-bearing geological units have been observed from orbit, distributed across the planet (Bibring and Langevin, 2008), and Murchie et al (2009) described five distinct classes of sulfates that express a range of co-occurring minerals and layer-forming tendencies.…”

“…Sulfate minerals are widespread, having been detected or inferred from elemental chemistry at every Mars landing site to date (Toulmin et al, 1977;Wänke et al, 2001;Squyres et al, 2004;Wang et al, 2006;Kounaves et al, 2010). Ca-, Mg-, and Fe-hydrated sulfates have also been identified from Mars orbit (e.g., Gendrin et al, 2005) in numerous locations correlated with expected locations of groundwater upwelling .…”