Abstract
AbstractThe scientific aims of the ExoMars Raman laser spectrometer (RLS) include identifying biological signatures and evidence of mineralogical processes associated with life. The RLS instrument was optimised to identify carbonaceous material, including reduced carbon. Previous studies suggest that reduced carbon on the Martian surface (perhaps originating from past meteoric bombardment) could provide a feedstock for microbial life. Therefore, its origin, form, and thermal history could greatly inform our understanding of Mars' past habitability. Here, we report on the Raman analysis of a Nakhla meteorite analogue (containing carbonaceous material) that was subjected to shock through projectile impact to simulate the effect of meteorite impact. The characterisation was performed using the RLS Simulator, in an equivalent manner to that planned for ExoMars operations. The spectra obtained verify that the flight‐representative system can detect reduced carbon in the basaltic sample, discerning between materials that have experienced different levels of thermal processing due to impact shock levels. Furthermore, carbon signatures acquired from the cratered material show an increase in molecular disorder (and we note that this effect will be more evident at higher levels of thermal maturity). This is likely to result from intense shearing forces, suggesting that shock forces within basaltic material may produce more reactive carbon. This result has implications for potential (past) Martian habitability because impacted, reduced carbon may become more biologically accessible. The data presented suggest the RLS instrument will be able to characterise the contribution of impact shock within the landing site region, enhancing our ability to assess habitability.
Highlights
Recent developments in instrument miniaturisation, robustness, and autonomy have led to Raman spectrometers being included on two of the most recent surface missions to Mars: there are two Raman systems on board NASA's Perseverance rover payload,[4,5] and a Raman spectrometer is included in the ESA ExoMars Rover's suite of analytical instruments.[6]
Recent investigations focusing on Archean rock samples have shown that the carbonaceous material present in the samples can be differentiated into populations based on levels of thermal maturity; that is, the characteristics of the socalled carbon D and G bands (Raman shifts of around 1350 cmÀ1 and between 1580 and 1600 cmÀ1, respectively[23]) can be used as indicators of structural organisation within the carbon
We report on the Raman analysis of a Nakhla meteorite analogue that was partially subjected to stress through a projectile impact
Summary
Raman spectroscopy has been identified as a powerful technique for the in situ analysis of surface material during planetary exploration surface missions.[1,2,3] Recent developments in instrument miniaturisation, robustness, and autonomy have led to Raman spectrometers being included on two of the most recent surface missions to Mars: there are two Raman systems on board NASA's Perseverance rover payload (launched in 2020),[4,5] and a Raman spectrometer is included in the ESA ExoMars Rover's suite of analytical instruments.[6]. A large number of studies have already been performed on the analysis of reduced carbon in meteorites[15,27] and in a range of terrestrial samples.[28,29,30,31] Recent investigations focusing on Archean rock samples have shown that the carbonaceous material present in the samples can be differentiated (spectrally) into populations based on levels of thermal maturity; that is, the characteristics of the socalled carbon D and G bands (Raman shifts of around 1350 cmÀ1 and between 1580 and 1600 cmÀ1, respectively[23]) can be used as indicators of structural organisation within the carbon. We discuss how thermal history and shock impacts of a sample affect the Raman spectra observed and determine the level to which such signatures can be identified when using the flight representative instrument
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