Remote detection of past habitability at Mars-analogue hydrothermal alteration terrains using an ExoMars Panoramic Camera emulator

J.K Harris,C.R Cousins,M Gunn,P.M Grindrod,D Barnes,I.A Crawford,R.E Cross,A.J Coates

doi:10.1016/j.icarus.2015.02.004

J.K Harris, C.R Cousins + Show 6 more

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https://doi.org/10.1016/j.icarus.2015.02.004

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Abstract

A major scientific goal of the European Space Agency’s ExoMars 2018 rover is to identify evidence of life within the martian rock record. Key to this objective is the remote detection of geological substrates that are indicative of past habitable environments, which will rely on visual (stereo wide-angle, and high resolution images) and multispectral (440–1000nm) data produced by the Panoramic Camera (PanCam) instrument. We deployed a PanCam emulator at four hydrothermal sites in the Námafjall volcanic region of Iceland, a Mars-analogue hydrothermal alteration terrain. At these sites, sustained acidic–neutral aqueous interaction with basaltic substrates (crystalline and sedimentary) has produced phyllosilicate, ferric oxide, and sulfate-rich alteration soils, and secondary mineral deposits including gypsum veins and zeolite amygdales. PanCam emulator datasets from these sites were complemented with (i) NERC Airborne Research and Survey Facility aerial hyperspectral images of the study area; (ii) in situ reflectance spectroscopy (400–1000nm) of PanCam spectral targets; (iii) laboratory X-ray Diffraction, and (iv) laboratory VNIR (350–2500nm) spectroscopy of target samples to identify their bulk mineralogy and spectral properties. The mineral assemblages and palaeoenvironments characterised here are analogous to neutral–acidic alteration terrains on Mars, such as at Mawrth Vallis and Gusev Crater. Combined multispectral and High Resolution Camera datasets were found to be effective at capturing features of astrobiological importance, such as secondary gypsum and zeolite mineral veins, and phyllosilicate-rich substrates. Our field observations with the PanCam emulator also uncovered stray light problems which are most significant in the NIR wavelengths and investigations are being undertaken to ensure that the flight model PanCam cameras are not similarly affected.

Highlights

The European Space Agency/Roscosmos rover “ExoMars”, scheduled for launch in 2018, has the primary objective of sampling the martian subsurface via a 2 m drill, and analysing the retrieved samples for geochemical and organic biosignatures (Vago et al, 2006)
Alteration and secondary minerals identified in the ASD laboratory Visible-Near Infrared (VNIR) spectra (Figure 3) include hematite, goethite, nontronite, montmorillonite, gypsum, and sulfur
Sample XRD analysis is consistent with the laboratory VNIR results, revealing alteration phases to include all the above, and kaolinite, anatase, natrojarosite, trace calcite and quartz

Summary

Introduction

The European Space Agency/Roscosmos rover “ExoMars”, scheduled for launch in 2018, has the primary objective of sampling the martian subsurface via a 2 m drill, and analysing the retrieved samples for geochemical and organic biosignatures (Vago et al, 2006) Key to this objective is the identification of geological and mineralogical surface deposits that are indicative of past habitable conditions. Each WAC is interfaced with a filter wheel containing 11 filters of pre-determined wavelength, with all 22 filters dedicated to a particular scientific investigation (Table 1) Of these 22 filters, 6 are dedicated broadband red, green, and blue filters that will produce stereo colour composite images of the martian surface, while 12 filters are dedicated narrowband ‘geology’ filters that have been designed to capture and differentiate between the subtle spectral properties of phyllosilicates, sulfates, iron oxides, and major basaltic minerals within the limited Visible-Near Infrared (VNIR) wavelength range (440 – 1000 nm) captured by the PanCam Active Pixel Sensor (Cousins et al, 2010; 2012). Together with targeted monochrome and colour images provided by the HRC, WAC colour composite and multispectral data will be used for palaeoenvironmental interpretation of surface deposits and subsequent drill target selection

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