Novel solvent systems for in situ extraterrestrial sample analysis

The life marker chip (LMC) is being designed to test for the chemical signature of life in the soil and rocks of Mars. It will use an antibody array as part of its detection and characterisation system and aims to detect both polar and non-polar molecules at the sub-ppm to tens of ppb level. It is necessary to use a solvent to transfer organic compounds from the Martian samples to the LMC itself, but organic solvents such as dichloromethane or hexane, commonly used to dissolve non-polar molecules, are incompatible with the LMC antibodies. Hence, an aqueous-based solvent capable of dissolving the biomarkers that might exist in the soil or rocks of Mars is required. Solvent extractions of a Martian soil analogue, JSC Mars-1, spiked with a range of standards show that a 20:80 (vol:vol) mixture of methanol and water is incapable of extracting compounds insoluble in water. However, addition of 1.5 mg ml⁻¹ of the surfactant polysorbate 80 produces extraction efficiencies of the aliphatic standards, hexadecane and phytane, equal to 25-30% of those produced by the common organic solvent mixture 93:7 (vol:vol) dichloromethane:methanol. Extraction of squalene and stigmasterol using the polysorbate solution is less efficient but still successful, at 5-10% of the efficiency of 93:7 dichloromethane:methanol. Such aliphatic compounds with occasional functional groups represent the compound classes to which most fossil organic biomarkers belong. The polysorbate solution did not extract the aromatic compounds pyrene and anthracene with great efficiency. A solvent of 20:80 methanol:water with 1.5 mg ml⁻¹ polysorbate 80 is therefore capable of selectively extracting aliphatic biomarkers from Martian samples and transferring them to the antibody sites on the life marker chip.     

Digging deep for ice in Isidis Planitia—New constraints on subsurface volatile concentrations from thermal modeling

The Isidis Planitia region on Mars usually is regarded as a comparably attractive site for landing missions based on engineering constraints such as elevation and smooth regional topography. The Mars Express landed element Beagle 2 was deployed to this area, and the southern margin of the basin was selected as one of the backup landing sites for the NASA Mars Exploration Rovers.Especially in the context of the Beagle 2 mission, Isidis Planitia has been discussed as a place which might have experienced a volatile-rich history with associated potential for biological activity [e.g. Bridges et al., 2003. Selection of the landing site in Isidis Planitia of Mars Probe Beagle 2. J. Geophys. Res. 108(E1), 5001, doi: 10.1029/2001JE001820]. However the measurements of by the GRS instrument on Mars Odyssey indicate a maximum inferred water abundance of only 3 wt% in the upper few meters of the surface [Feldman et al., 2004. Global distribution of near-surface hydrogen on Mars. J. Geophys. Res. 109, E09006, doi: 10.1029/2003JE002160]. Based on these measurements this area seems to be one of the driest spots in the equatorial region of Mars.To support future landing site selections we took a more detailed look at the minimum burial depth of stable ice deposits in this area, focusing as an example on the planned Beagle 2 landing site. We are especially interested in the likelihood of ground ice deposits within the range of proposed subsurface sampling tools as drills or ‘mole’-like devices [Richter et al., 2002. Development and testing of subsurface sampling devices for the Beagle 2 Lander. Planet. Space Sci. 50, 903-913] given reasonable physical constraints for the surface and near surface material.For a mission like ExoMars [Kminek, G., Vago, J.L., 2005. The Aurora Exploration Program—The ExoMars Mission. In: Proceedings of the 35th Lunar and Planetary Science Conference, abstract no. 1111, 15-19 March 2004, League City, TX] with a focus on finding traces of fossil life the area might be of potential interest, because these traces would be better conserved in the dry soil. Modeling and measurement indicate that Isidis Planitia is indeed a dry place and any hypothetical ground ice deposits in this region are out of range of currently proposed sampling devices.     

Soil simulant sourcing for the ExoMars rover testbed

ExoMars is the European Space Agency (ESA) mission to Mars planned for launch in 2018, focusing on exobiology with the primary objective of searching for any traces of extant or extinct carbon-based micro-organisms. The on-surface mission is performed by a near-autonomous mobile robotic vehicle (also referred to as the rover) with a mission design life of 180 sols (Patel et al., 2010). In order to obtain useful data on the tractive performance of the ExoMars rover before flight, it is necessary to perform mobility tests on representative soil simulant materials producing a Martian terrain analogue under terrestrial laboratory conditions. Three individual types of regolith shown to be found extensively on the Martian surface were identified for replication using commercially available terrestrial materials, sourced from UK sites in order to ensure easy supply and reduce lead times for delivery. These materials (also referred to as the Engineering Soil (ES-x) simulants) are: a fine dust analogue (ES-1); a fine aeolian sand analogue (ES-2); and a coarse sand analogue (ES-3). Following a detailed analysis, three fine sand regolith types were identified from commercially available products. Each material was used in its off-the-shelf state, except for ES-2, where further processing methods were used to reduce the particle size range. These materials were tested to determine their physical characteristics, including the particle size distribution, particle density, particle shape (including angularity/sphericity) and moisture content. The results are analysed to allow comparative analysis with existing soil simulants and the published results regarding in situ analysis of Martian soil on previous NASA (National Aeronautics and Space Administration) missions. The findings have shown that in some cases material properties vary significantly from the specifications provided by material suppliers. This has confirmed the need for laboratory testing to determine the actual parameters to prove that standard geotechnical processes are indeed suitable. The outcomes have allowed the confirmation of each simulant material as suitable for replicating their respective regolith types.