51st Lunar and Planetary Science Conference (2020) 2590.pdf

DEVELOPMENT OF OXIA PLANUM SIMULANT RELEVANT TO THE EXOMARS MISSION. A. Dugdale1, N. K. Ramkissoon2, P. Fawdon3, S. M. R. Turner2, S. P. Schwenzer2, K. Olsson-Francis2 and V. K. Pearson2. 1Biology Department, Maynooth University, Maynooth, Kildare, Ireland. 2AstrobiologyOU, STEM Faculty, The Open University Milton Keynes, MK7 6AA, UK. 3School of Physical Sciences, STEM Faculty, The Open University, Milton Keynes, MK7 6AA, UK. (Corresponding author:[email protected]).

Introduction: The ExoMars rover is due to land data and in situ data from MSL at Gale crater. CRISM on Mars in the spring of 2021. The key objectives of is capable of acquiring data representative of particle this mission are to search for signs of life, past or depth of 1-10s μm. This data is then integrated present, and characterise the geochemical/water horizontally, providing data on spatial distribution of environment as a function of depth [1]. To achieve minerals. CheMin on the other hand is capable of this, Oxia Planum, a clay-rich plain located between vertical analyses, taking measurements from an area of Mawrth Vallis and Ares Vallis, has been selected as ~10s mm3 beneath the surface, providing definite the landing site, due to abundant mineralogical quantitative mineralogy data. CRISM and CheMin evidence of aqueous activity and its astrobiological therefore provide data that can be used in conjunction potential [2,3]. To assist in data interpretation to understand minerology [12]. For example, the simulants mimicking the region’s mineralogy are quantity of olivine and high- calcium pyroxene in Gale required. The aim of this project is to develop regolith crater was higher when analysed in situ by MSL, while simulants that can be used to assist in the interpretation alkali feldspars were not observed from orbit but were of data returned from the ExoMars rover mission and detected by MSL [13, 14]. Using geological and in habitability investigations. mineralogical data from remote sensing, 5 simulant Target mineralogy: Differential erosion rates at lithologies have been identified representing the Oxia Planum have exposed three distinct units [4]: stratigraphy in the clay unit (Table 1). 1) A clay unit (mid-Noachian in age) is concentrated Characterisation: Simulants will be made from in the eastern outcrop. These clays likely formed due terrestrial analog materials and characterized using to mafic/ultramafic or rock water interaction causing instruments akin to RLS (Raman Laser Spectrometer) alteration of montmorillite and nontronite [5]. CRISM and ISEM (Infrared Spectrometer for ExoMars) data shows the presence of Fe-phyllosilicates as well instruments on board the ExoMars rover as well as as sporadic Al-phyllosilicates to overlay Fe- standard geological techniques, such as Scanning phyllosilicates. Such layering is evidence of a electron microscopy (SEM) and electron microprobe weathering profile in an aqueous environment [6,7]. analysis in order to refine mineral chemistries. Clays are indicative of once aqueous environments, Uses: These simulants can be used to help interpret active chemistries and perhaps habitability, as clay data returned from instruments onboard the ExoMars particles act as reaction vessels for organic molecules. rover from a range of potential lithologies that could On Earth biochemistries and microbe clay interactions be found at Oxia Planum. Additionally, these are observed at Al/Fe clay boundaries [9, 10]. These simulants incorporate the longitudinal mineralogical layers are also thought to be deep enough to preserve changes in the clay unit, relevant to the ExoMars drill. biosignatures if present, such as organic molecules They could also be used in a range of experiments to that can be damaged by ionising radiation [8]. assess the habitability of this region. 2) A depositional unit (late Noachian in age), Acknowledgements: AD and NKR would like to thank the potentially a fluvial deltaic fan, in which hydrated RAS for funding towards this work. References: [1] J.L. Vago and F. Westall, Astrobiology Vol. 17, silica is detected. Concentrated in the southern No. 471-510, 2017. [2] C. Quantin-Nataf et al., International Conference outcrop, this unit has little astrobiological potential, on Mars, Lunar and Planetary Institute. Vol. 9, No. 2089, pp. 6317, with no clays present. [2,4]. 2019. [3] J. Carter et al., EPSC Abstracts Vol. 13, No. 445, 2019 [4] J. 3) A younger volcanic unit (Amazonian in age) that Carter et al., 2019 LPSC Vol. 47, No.2064, 2016 [5] D. Loizeau et al., Journal of Geophysical Research: Planets, Vol. 112 No. 8, 2007. [6] C. protected the underlying clay and deltaic units from Quantin et al., EPSC Vol. 10 No. 704, 2015. [7] F. Da Pieve et al., Icarus erosion. It is thought to be rich in pyroxene and Vol. 300, pp458-76, 2019. [8] G. Kminek and J. Bada Earth and plagioclase (similar to units at Mawrth Vallis) [7,11]. Planetary Science Letters, Vol. 245 No.1-2, pp.1-5, 2006. [7] J.C. Simulant design: CRISM data suggests Mawrth Bridges, et al., LPSC Abstract Vol 49, No. 2083, pp2177, 2018. [9]C. Quantin et al., LPSC abstract, Vol. 47, No. 2863, 2016 [10] J. Bishop Vallis has a similar formation history to Oxia Planum, et al., Planetary and Space Science, Vol.86, pp. 130-149, 2013 [11] C. both exhibiting diverse mineralogy, characteristic of Quantin-Nataf et al., Submitted to Astrobiology, 2019. [13] K.D. Seelos once aqueous environments [11]. Therefore, we have et al., Geophys. Res. Lett., Vol 41 No. 14, pp.4880-4887, 2014. [14] M.S. used mineralogical information from Mawrth Vallis to Rice et al., J. Geophys. Res.: Planets, Vol.122, No.1 pp.2-20, 2017. [15]J. Wray et al., Geophysical Research Letters, Vol.35 No. 12, 2008. refine mineral selection for Oxia Planum simulants. [16] S.M Turner and J.C Bridges, Lunar and Planetary Science We have also made adjustments to mineral Conference Vol. 48 No. 2228, 2017. [17] N.K. Ramkissoon et al., compositions based on discrepancies between orbital Planetary and Space Science, p. 104722, 2019. 51st Lunar and Planetary Science Conference (2020) 2590.pdf

Table 1: Proposed simulants for Oxia Planum clay unit, based on minerology at Oxia Planum and Mawrth Vallis.

Simulant Mineralogy Justification for minerology References Simulant one: Major component: This simulant represents the upper clay [5,11,15,16] Al-rich layer Al- smectite layer. (montmorillonites), Al-rich clays are identified at 2.2μm band kaolinite (OMEGA). Minor Component: Allophane and hematite are added, these Allophane, hydrated minerals were detected in Al- rich layers at silica, sulfate, Mawrth Vallis. hematite, zeolite, Sulfates are detected in pockets within clay plagioclase. layer. Zeolite and plagioclase are added to all simulants as small quantities of both are detected at clay units at Mawrth Vallis. Simulant two: Major component: Addition of iron hydroxide and iron oxide [11] Al-rich clay Al- smectite to simulant one represents blending of with ferrous (montmorillonites), above Al-rich clays with a ferrous layer material kaolinite between Al and Fe- rich clays as detected Minor Component: at Mawrth Vallis. Allophane, sulfate, hematite, zeolite, plagioclase iron hydroxide, iron oxide Simulant three: Major component: This simulant represents underlying Fe- [5,11,16] Fe rich layer Fe-smectite rich layer consisting of vermiculite, Ferron (vermiculites, saponite and berthierite. saponite and Absorbance bands at 1.4, 1.9, 2.3 μm berthierite) (OMEGA) consistent with Fe-smectites. Minor component: CRISM detection of olivine and pyroxene Olivine, pyroxene, in Fe- rich clay layer. At the centre of the zeolite, plagioclase landing site an orange colour is observed possible sulfate. due to Fe/Mg-clay olivine mixture. Sulfates are possible additions as presence of sulfate reservoir is hypothesised below Fe-rich clays at Mawrth Vallis. Simulant four: Major component: Addition of iron hydroxide and iron oxide [11] Fe-rich layer Fe-smectite to simulant three represents blending of with ferrous (vermiculites, below Fe-rich clays with a ferrous layer material. saponite and between Al and Fe-rich clays as detected berthierite) at Mawrth Vallis. Minor component: Olivine, pyroxene, zeolite, plagioclase possible sulfates, iron hydroxide, iron oxide. Simulant five: Minerology CRISM data is unclear about the clay’s Fe [11,17] Fe-rich layer consistent simulant speciation, with variation in Fe spectral with varied four with the iron absorption (1-1.7μm), likely due to Fe2+/Fe3+ ratio. component’s Fe2+/Fe3+ variation. It is also not clear if oxidation state Fe2+ detected is due to smectite or olivine. adjusted. Therefore, it will be possible to vary the Fe3+/Fe2+ ratio as in [17].