Spectral identification and quantification of salts in the Atacama Desert

This work was part-funded by a Research Incentive Grant from The Carnegie Trust (REF: 70335) and a Royal Society of Edinburgh Research Fellowship to C. Cousins. J, Harris acknowledges funding from STFC (consolidated grant ST/N000528/1).Salt minerals are an important natural resource. The ability to quickly and remotely identify and quantify salt deposits and salt contaminated soils and sands is therefore a priority goal for the various industries and agencies that utilise salts. The advent of global hyperspectral imagery from instruments such as Hyperion on NASA’s Earth-Observing 1 satellite has opened up a new source of data that can potentially be used for just this task. This study aims to assess the ability of Visible and Near Infrared (VNIR) spectroscopy to identify and quantify salt minerals through the use of spectral mixture analysis. The surface and near-surface soils of the Atacama Desert in Chile contain a variety of well-studied salts, which together with low cloud coverage, and high aridity, makes this region an ideal testbed for this technique. Two forms of spectral data ranging 0.35 – 2.5 μm were collected: laboratory spectra acquired using an ASD FieldSpec Pro instrument on samples from four locations in the Atacama desert known to have surface concentrations of sulfates, nitrates, chlorides and perchlorates; and images from the EO-1 satellite’s Hyperion instrument taken over the same four locations. Mineral identifications and abundances were confirmed using quantitative XRD of the physical samples. Spectral endmembers were extracted from within the laboratory and Hyperion spectral datasets and together with additional spectral library endmembers fed into a linear mixture model. The resulting identification and abundances from both dataset types were verified against the sample XRD values. Issues of spectral scale, SNR and how different mineral spectra interact are considered, and the utility of VNIR spectroscopy and Hyperion in particular for mapping specific salt concentrations in desert environments is established. Overall, SMA was successful at estimating abundances of sulfate minerals, particularly calcium sulfate, from both hyperspectral image and laboratory sample spectra, while abundance estimation of other salt phase spectral end-members was achieved with a higher degree of error.Publisher PD

The ExoMars Spectral Tool (ExoSpec):an image analysis tool for ExoMars 2020 PanCam imagery

The upcoming launch of the European Space Agency (ESA) ExoMars 2020 rover signals a need for an analysis tool to be created which can exploit the multi- and hyperspectral data that will be returned by its Panoramic Camera (PanCam), Infrared Spectrometer for Mars (ISEM), and Close-UP Imager (CLUPI) instruments. Data processed by this analysis tool will be invaluable in (i) characterising the geology local to the ExoMars rover, (ii) relating ground-based observations to orbital Compact Reconnaissance Imaging Spectrometer for Mars (CRISM) data, (iii) detecting evidence of past habitability on Mars, and (iv) identifying drilling locations. PanCam, ISEM, and CLUPI offer spectral analysis capabilities in both spatial (140-1310 microns/pixel at 2 m working distance) and spectral (440-3300 nm) dimensions. We have developed the ExoMars Spectral Tool (ExoSpec) which functions as a GUI-based extension to ENVI + IDL and performs steps from image import and compilation into ENVI.dat format, flat-fielding, radiometric correction, radiance-toreflectance (R∗) corrections using the in-scene Gretag MacBeth ColorCheckerTM, and calculation of spectral parameters. We demonstrate the functionality of ExoSpec at its current stage of development and illustrate its utility with results from field expeditions to Mars analogue terrains in: (i) geothermally altered basalts in Ńamafjall, Iceland, and (ii) layered alluvial plains deposits in Hanksville, USA, using ExoMars PanCam, ISEM, and CLUPI emulator instruments

Natural Analogue Constraints on Europa's Non-ice surface Material

Non-icy material on the surface of Jupiter’s moon Europa is hypothesised to have originated from its subsurface ocean, and thus provide a record of ocean composition and habitability. The nature of this material is debated, but observations suggest that it comprises hydrated sulfate and chloride salts. Analogue spectroscopic studies have previously focused on single phase salts under controlled laboratory conditions. We investigated natural salts from perennially cold (<0 °C) hypersaline springs, and characterised their reflectance properties at 100 K, 253 K and 293 K. Despite similar major ion chemistry, these springs form mineralogically diverse deposits, which when measured at 100 K closely match reflectance spectra from Europa. In the most sulfate-rich samples, we find spectral features predicted from laboratory salts are obscured. Our data are consistent with sulfate-dominated europan non-icy material, and further, show that the emplacement of endogenic sulfates on Europa’s surface would not preclude a chloride-dominated ocean

Selecting the geology filter wavelengths for the ExoMars Panoramic Camera Instrument

The Panoramic Camera (PanCam) instrument will provide surface remote sensing data for the ExoMars mission. A combination of wide-angle stereo, multispectral, and high resolution imagery will generate contextual geological information to help inform which scientific targets should be selected for drilling and analysis. One component of the PanCam dataset is narrowband multispectral imaging in the visible to near infrared, which utilises a dedicated set of 12 “geology” filters of predetermined wavelength and bandwidth to view the terrain, and provide information on composition and putative mineralogy. The centre wavelengths and bandwidths of these filters were optimised to account for the highly diverse mineralogical terrains the ExoMars rover will hopefully encounter. Six new alternative test filter sets were created, each optimised for the detection of either: sulfates, phyllosilicates, ferric oxides, mafic silicates, iron absorptions, and minor hydration absorptions. These six filter sets were cross-tested using database mineral reflectance spectra and Mars analogue rock multispectral data to find the best performing filter set. Once selected, the bandwidths of this filter set were also optimised. The filter set optimised to ferric oxide minerals was able to most accurately represent rock multispectral data, as well as capture subtle spectral features of hydrated minerals, including sulfates, phyllosilicates, and carbonates. These filters differ from those used on past missions (e.g., Pathfinder, Mars Exploration Rover) and represent the next evolutionary stage in PanCam instrument development. When compared to past filter sets, the updated ExoMars filters capture rock and mineral spectral data more effectively, enhancing the ability of the ExoMars PanCam to detect lithological and compositional variation within an outcrop

Colour Peak:An analogue environment for the waters of late Noachian Mars

The surface of Mars cannot sustain liquid water today, but there is evidence water was present during the Noachian era. The transition of the martian climate from the wet Noachian to the dry Hesperian would have resulted in saline and sulfur rich surface waters . Terrestrial analogue environments that possess a chemistry like these proposed waters can be used to develop an understanding of organisms that could have persisted under such conditions. Here we present the chemistry and microbiome of the analogue environment Colour Peak, a sulfidic and saline spring system located within the Canadian High Arctic. In this study, molecular and geochemical techniques were used to investigate the sediment of the Colour Peak springs. Nucleic acids were extracted from the microbes in the sediments and the microbiome was characterised by the amplification and sequencing of 16S rRNA gene amplicons. The elemental composition of the fluids and sediment was determined by ICP-OES and compared with brines determined from the chemistry of the “Rocknest” sand sample at Yellowknife Bay, Gale Crater (Mars) by thermochemical modelling. Gibbs energy values were calculated from this fluid chemistry to identify potentially viable metabolisms. Analysis of the chemistries of the Colour Peak fluids confirmed a chemical composition like the thermochemically modelled fluid, with this justifying the classification of Colour Peak as an appropriate analogue environment to investigate the habitability of former martian aqueous environments. 16S rRNA gene profiling of the Colour Peak microbial community revealed it was dominated by bacteria associated with oxidation of reduced sulfur species and carbon dioxide fixation. Gibbs energy values calculated using the chemistry of the modelled martian fluid demonstrated that the oxidation of reduced sulfur species was also viable in this chemical environment under aerobic and anaerobic conditions. These results demonstrate that microbial sulfide oxidation is thermodynamically viable using both modelled and environmental proxies for former martian aqueous environments. This study highlights that metabolisms utilising the oxidation of reduced sulfur species could have been thermodynamically viable in ancient martian aqueous environments. Further work is needed to assess this proposed viability and the potential for unambiguous biosignature formation

Colour Peak: An analogue environment for late Noachian Mars

The martian surface cannot sustain liquid water today, but there is evidence water was present during the Noachian era. The transition of the martian climate into the Hesperian would have resulted in saline and sulfuric waters. Terrestrial analogue environments that possess a chemistry like these proposed waters can be used to develop an understanding of organisms that could have persisted. Here we present the chemistry and microbiome of Colour Peak, a sulfidic and saline spring system located within the Canadian High Arctic. Nucleic acids were extracted from the microbes in the sediments and the microbiome was characterised by the amplification and sequencing of 16S rRNA gene amplicons. The elemental composition of the fluids and sediment was determined by ICP-OES and compared with brines determined from the chemistry of the “Rocknest” sample at Yellowknife Bay, Gale Crater (Mars) by thermochemical modelling. Gibbs energy values were calculated from this fluid chemistry to identify potentially viable metabolisms. Analysis of the chemistries of the Colour Peak fluids confirmed a composition like the thermochemically modelled fluid, providing justification for the classification of Colour Peak as an appropriate analogue environment to investigate the habitability of former martian waters. Profiling of the Colour Peak microbial community revealed domination by bacteria associated with oxidation of reduced sulfur species and carbon dioxide fixation. Gibbs energy values calculated using the modelled martian fluid chemistry demonstrated that oxidation of reduced sulfur species was also viable in this chemical environment under aerobic and anaerobic conditions. These results demonstrate microbial sulfide oxidation is thermodynamically viable using both modelled and environmental proxies for former martian aqueous environments. This study highlights that metabolisms utilising the oxidation of reduced sulfur species could have been thermodynamically viable in ancient martian aqueous environments. Further work is needed to test this viability and the subsequent potential for biosignature formation