Hydrothermal environments driven by volcanism are prime astrobiological targets on Mars, due to their ability to support and preserve microbial ecosystems. Volcano -ice interactions on On Earth, volcano -ice interactions produce many hydrothermal habitats available to microbial colonisation, and thus provide an analogue to past environments on Mars, where many landforms have been attributed to volcano -cryospheric interaction. However, Mars exploration urgently requires a framework for identifying such environments on a range of scales and with a range of geological criteria. In this paper rRemote sensing data were combined with sub-mm environmental mapping and sample analysis that included (X-ray diffraction, Raman spectroscopy, thin section petrography, scanning electron microscopy, electron dispersive spectrometer analysis, and dissolved ion water chemistry,) to characterise samples from two areas of basaltic volcano -ice interaction: namely Askja and Kverkfjöll volcanoes in Iceland. Askja was erupted subglacially during the Pleistocene, and is now exposed within a volcanic desert. Kverkfjöll is a subglacial volcano beneath on the northern margin of Vatnajökull ice cap, and hosts active hydrothermal systems. NE-trending fissure swarm ridges extend between these two volcanic systems. Multiple Holocene glacial outburst (jökulhlaup) sedimentary deposits lie to the north of Kverkfjöll. Hydrothermal environments at Kverkfjöll were found to be predominantly acidic, with dissolved sulphate dominating the water chemistry. These hydrothermal environments vary across a small (<100 m) spatial scale, and include hot springs, anoxic pools, meltwater lakes, and sulphur-and iron-depositing fumaroles. Biomats, two in association with individual goethite and pyrite mineral terraces, were common at Kverkfjöll. In-situ and laboratory VNIR (440 -1000 nm) reflectance spectra representative of Mars rover multispectral imaging show spectral profiles to be influenced by Fe 2+/3+ -bearing minerals. Overall, sediments and lavas display two types of hydrothermal alteration: a low-temperature (<120°C) assemblage dominated by palagonite, sulfates, and iron oxides; and a high-temperature (>120°C) assemblage signified by heulandite and quartz. This Overall, this work provides a framework for identifying such environments during future exploration of Mars, given their high astrobiological potential, and Claire Cousins -BBK 14/08/12 3 provides a descriptive reference for the two prominent active hydrothermal environments at Kverkfjöllwhich can be used as analogues for those on Mars.

This paper is dedicated to the late Prof. Dave Barnes who sadly passed away before the publication of this work, to which he had significantly contributed over the years through his work on the ExoMars PanCamA 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?1000 nm) data produced by the Panoramic Camera (PanCam) instrument. We deployed a PanCam emulator at four hydrothermal sites in the N?mafjall 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?1000 nm) of PanCam spectral targets; (iii) laboratory X-ray Diffraction, and (iv) laboratory VNIR (350?2500 nm) 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 affectedpublishersversionPeer reviewe

Abstract-The mineralogy of Mars is well understood on a qualitative level at a global scale due to satellite data. Quantitative analysis of visible and near-infrared (VNIR) satellite data is a desirable but nontrivial task, due partly to the nonlinearity of VNIR reflectance spectra from the mineral mixtures of the Martian surface. In this study, we investigated the use of the Hapke radiative transfer model to generate linearly mixed single scattering albedo data from nonlinearly mixed VNIR reflectance data and then quantitatively analyzed them using the linear spectral mixture model. Simplifications to the Hapke equation were tested accounting for variables that would be unknown when using satellite data. Mineral mixture spectra from the RELAB spectral library were degraded to test the robustness of the unmixing technique in the face of data that mimic some of the complexities of satellite spectral data collected at Mars. A final test was performed on spectra from shergottite meteorites to assess the technique against real Martian mineral mixtures. The simplified Hapke routine produced robust abundance estimates within 5-10% accuracy when applied to laboratory standard spectra from the synthetic mixtures of igneous minerals in agreement with previous studies. The results of tests involving degraded data to mimic the low spectral contrast of the Martian surface and the lack of a priori knowledge of the constituent mineral spectral endmembers, however, were less encouraging, with errors in abundance estimation greater than 25%. These results cast doubt on the utility of Hapke unmixing for the quantitative analysis of VNIR data of the surface of Mars.