Identification of fluids accompanying bio-signature formation in martian analogue experiments

Introduction: Geological, geochemical and geomorphological evidence collected by orbiting spacecrafts and rovers (e.g. Curiosity, Opportunity) on Mars suggests the presence of impact-generated hydrothermal systems and fluvio-lacustrine environments that may have been habitable in the Noachian - early Hesperian [1-2]. However, finding evidence that life has existed on Mars is dependent on the identification of bio-signatures that testify biological processes have occurred in martian aqueous environments. Owing to the detrimental effect that the conditions at the surface of Mars have on organic molecules [3, 4], inorganic biosignatures, such as secondary alteration minerals associated with microbial activity, may be more appropriate for assessing whether life existed on early Mars. Clay minerals, carbonates and sulfates found at Gale and Jezero craters are considered to have formed in extinct aqueous systems following basalt weathering and / or brine evaporation [5, 6]. At present, it is not possible to determine unambiguously whether the formation of these alteration minerals is the result of biotic weathering or solely related to the interaction of martian brines with rocks of basaltic composition. Laboratory experiments and field studies can only study basalt weathering under abiotic and biotic conditions over short timeframes (days to months). By contrast, thermochemical modelling can be used to study alteration processes that can occur over geological time scales, owing to its capability to predict secondary mineral assemblages and variations in fluid chemistries through the assessment of reaction pathways during water-rock interaction [7-9]. By combining laboratory experiments and thermochemical modelling it is possible to investigate alteration mineral and brine chemistries that may form biotically and abiotically during basalt weathering over a range of different time scales [10]