Oxalate formation under the hyperarid conditions of the Atacama desert as a mineral marker to provide clues to the source of organic carbon on Mars

In this study, we report the detection and characterization of the organic minerals weddellite (CaC2O4 · 2H2O) and whewellite (CaC2O4 · H2O) in the hyperarid, Mars-like conditions of the Salar Grande, Atacama desert, Chile. Weddellite and whewellite are commonly of biological origin on Earth and have great potential for preserving records of carbon geochemistry and possible biological activity on Mars if they are present there. Weddellite and whewellite have been found as secondary minerals occurring inside the lower detrital unit that fills the Salar Grande basin. The extremely low solubility of most oxalate minerals inhibits detection of oxalate by ion chromatography (IC). Crystalline oxalates, including weddellite and whewellite, were detected by X-ray diffraction (XRD). The association of weddellite with surface biota and its presence among subsurface detrital materials suggest the potential of a biological origin for Salar Grande weddellite and whewellite. In this regard, biological activity is uniquely capable of concentrating oxalates at levels detectable by XRD. The complementary detection of oxalate-bearing phases through IC in the upper halite-rich unit suggests the presence of a soluble oxalate phase in the basin that is not detected by XRD. The formation, transport, and concentration of oxalate in the Salar Grande may provide a geochemical analogue for oxalate-bearing minerals recently suggested to exist on Mars

Ceres' spectral link to carbonaceous chondrites - Analysis of the dark background materials

Ceres’ surface has commonly been linked with carbonaceous chondrites (CCs) by ground‐based telescopic observations, because of its low albedo, flat to red‐sloped spectra in the visible and near‐infrared (VIS/NIR) wavelength region, and the absence of distinct absorption bands, though no currently known meteorites provide complete spectral matches to Ceres. Spatially resolved data of the Dawn Framing Camera (FC) reveal a generally dark surface covered with bright spots exhibiting reflectance values several times higher than Ceres’ background. In this work, we investigated FC data from High Altitude Mapping Orbit (HAMO) and Ceres eXtended Juling (CXJ) orbit (~140 m/pixel) for global spectral variations. We found that the cerean surface mainly differs by spectral slope over the whole FC wavelength region (0.4–1.0 μm). Areas exhibiting slopes <−10% μm−1 constitute only ~3% of the cerean surface and mainly occur in the bright material in and around young craters, whereas slopes ≥−10% μm−1 occur on more than 90% of the cerean surface; the latter being denoted as Ceres’ background material in this work. FC and Visible and Infrared Spectrometer (VIR) spectra of this background material were compared to the suite of CCs spectrally investigated so far regarding their VIS/NIR region and 2.7 μm absorption, as well as their reflectance at 0.653 μm. This resulted in a good match to heated CI Ivuna (heated to 200–300 °C) and a better match for CM1 meteorites, especially Moapa Valley. This possibly indicates that the alteration of CM2 to CM1 took place on Ceres

Fitting the curve in Excel®:Systematic curve fitting of laboratory and remotely sensed planetary spectra

Spectroscopy in planetary science often provides the only information regarding the compositional and mineralogical make up of planetary surfaces. The methods employed when curve fitting and modelling spectra can be confusing and difficult to visualize and comprehend. Researchers who are new to working with spectra may find inadequate help or documentation in the scientific literature or in the software packages available for curve fitting. This problem also extends to the parameterization of spectra and the dissemination of derived metrics. Often, when derived metrics are reported, such as band centres, the discussion of exactly how the metrics were derived, or if there was any systematic curve fitting performed, is not included. Herein we provide both recommendations and methods for curve fitting and explanations of the terms and methods used. Techniques to curve fit spectral data of various types are demonstrated using simple-to-understand mathematics and equations written to be used in Microsoft Excel® software, free of macros, in a cut-and-paste fashion that allows one to curve fit spectra in a reasonably user-friendly manner. The procedures use empirical curve fitting, include visualizations, and ameliorates many of the unknowns one may encounter when using black-box commercial software. The provided framework is a comprehensive record of the curve fitting parameters used, the derived metrics, and is intended to be an example of a format for dissemination when curve fitting data

Infrared spectroscopic characterization of organic matter associated with microbial bioalteration textures in basaltic glass

Microorganisms have been found to etch volcanic glass within volcaniclastic deposits from the Ontong Java Plateau, creating micron-sized tunnels and pits. The fossil record of such bioalteration textures is interpreted to extend back ∼3.5 billion years to include meta-volcanic glass from ophiolites and Precambrian greenstone belts. Bioalteration features within glass clasts from Leg 192 of the Ocean Drilling Program were investigated through optical microscopy and Fourier transform infrared (FTIR) spectroscopy of petrographic thin sections. Extended depth of focus optical microscopic imaging was used to identify bioalteration tubules within the samples and later combined with FTIR spectroscopy to study the organic molecules present within tubule clusters. The tubule-rich areas are characterized by absorption bands indicative of aliphatic hydrocarbons, amides, esters, and carboxylic groups. FTIR analysis of the tubule-free areas in the cores of glass clasts indicated that they were free of organics. This study further constrains the nature of the carbon compounds preserved within the tubules and supports previous studies that suggest the tubules formed through microbial activity

Salt – A critical material to consider when exploring the solar system

International audienc

Complex Water-ice Mixtures on NII Nereid: Constraints from NIR Reflectance

Nereid, Neptune's third-largest satellite, lies in an irregular orbit and is the only outer satellite in the system (apart from Triton) that can be spectroscopically characterized with the current generation of Earth-based telescopes. We report our results on the spectral characterization of Nereid using its reflectance spectrum from 0.8 to 2.4 μm, providing the first measurements over the range of 0.8-1.4 μm. We detect spectral absorption features of crystalline water ice in close agreement with previous measurements. We show that model fits of simple intimate mixtures including water ice do not provide simultaneous matches to absorption band depths at 1.5 and 2.0 μm when accounting for the spectral continuum. Possible solutions include invoking a more complex continuum, including both crystalline and amorphous water ice, and allowing for submicron-sized grains. We show that mixtures including magnetite and the CM2 chondrite Murchison provide a flexible framework for interpreting spectral variation of bodies with neutral-sloped spectra like that of Nereid. Magnetite in particular provides a good match to the spectral continuum without requiring the presence of tholin-like organics. We note that carbonaceous chondrites and their components may be useful analogs for the non-ice components of outer solar system bodies, consistent with recent findings by Fraser et al. Comparison to spectra of large trans-Neptunian objects and satellites of Uranus show that Nereid's low albedo, deep water bands, and neutral color is distinct from many other icy objects, but such comparisons are limited by an incomplete understanding of spectral variability among ∼100 km-sized icy bodies 2021. The Author(s). Published by the American Astronomical Society. © 2021. The Author(s). Published by the American Astronomical Society.Open access journalThis item from the UA Faculty Publications collection is made available by the University of Arizona with support from the University of Arizona Libraries. If you have questions, please contact us at [email protected]

Reflectance spectroscopy (200-2500nm) of highly-reduced phases under oxygen- and water-free conditions

Spectra of highly-reduced mineral phases from 200 to 2500 nm provide new laboratory constraints on the surfaces of asteroids and other extremely reduced solid assemblages. Synthetic oldhamite (CaS) is distinguished by high ultraviolet reflectance (which decreases toward shorter wavelengths). Oldhamite and osbornite spectra show absorption features at ∼401 nm and ∼436 nm, respectively. Chemically pure synthetic oldhamite is spectrally distinct from naturally-occurring oldhamite from the Norton County aubrite, possibly due to differences in minor and trace element compositions, presence or absence of inclusions, or differences in oxidation/hydration (terrestrial weathering). Iron powders at 50 nm and 10 μm nominal particle sizes, nanophase graphite, and carlsbergite (CrN) all have very low reflectivity over the 200–2500 nm wavelength range. Carlsbergite has a slight blue spectral slope in the visible and near-infrared (400–2500 nm), while the iron powders and nanophase graphite show slight red slopes over this wavelength range

Evidence for life in the isotopic analysis of surface sulphates in the Haughton impact structure, and potential applications on Mars

The analysis of sulphur isotopic compositions in three sets of surface sulphate samples from the soil zone in the Haughton impact structure shows that they are distinct. They include surface gypsum crusts remobilized from the pre-impact gypsum bedrock (mean δ34S +31‰), efflorescent copiapite and fibroferrite associated with hydrothermal marcasite (mean δ34S −37‰), and gypsum-iron oxide crusts representing weathering of pyritic crater-fill sediments (mean δ34S +7‰). Their different compositions reflect different histories of sulphur cycling. Two of the three sulphates have isotopically light (low δ34S) compositions compared with the gypsum bedrock (mean δ34S +31‰), reflecting derivation by weathering of sulphides (three sets of pyrite/marcasite samples with mean δ34S of −41, −20 and −8‰), which had in turn been precipitated by microbial sulphate reduction. Thus, even in the absence of the parent sulphides due to surface oxidation, evidence of life would be preserved. This indicates that on Mars, where surface oxidation may rule out sampling of sulphides during robotic exploration, but where sulphates are widespread, sulphur isotope analysis is a valuable tool that could be sensitive to any near-surface microbial activity. Other causes of sulphur isotopic fractionation on the surface of Mars are feasible, but any anomalous fractionation would indicate the desirability of further analysis

Constraining the regolith composition of asteroid (16) psyche via laboratory visible near-infrared spectroscopy

(16) Psyche is the largest M-type asteroid in the main belt and the target of the NASA Discovery-class Psyche mission. Despite gaining considerable interest in the scientific community, Psyche's composition and formation remain unconstrained. Originally, Psyche was considered to be almost entirely composed of metal due to its high radar albedo and spectral similarities to iron meteorites. More recent telescopic observations suggest the additional presence of low-Fe pyroxene and exogenic carbonaceous chondrites on the asteroid's surface. To better understand the abundances of these additional materials, we investigated visible near-infrared (0.35-2.5 μm) spectral properties of three-component laboratory mixtures of metal, low-Fe pyroxene, and carbonaceous chondrite. We compared the band depths and spectral slopes of these mixtures to the telescopic spectrum of (16) Psyche to constrain material abundances. We find that the best matching mixture to Psyche consists of 82.5% metal, 7% low- Fe pyroxene, and 10.5% carbonaceous chondrite by weight, suggesting that the asteroid is less metallic than originally estimated (≈94%). The relatively high abundance of carbonaceous chondrite material estimated from our laboratory experiments implies the delivery of this exogenic material through low velocity collisions to Psyche's surface. Assuming that Psyche's surface is representative of its bulk material content, our results suggest a porosity of 35% to match recent density estimates. © 2021 The Author(s).Open access journalThis item from the UA Faculty Publications collection is made available by the University of Arizona with support from the University of Arizona Libraries. If you have questions, please contact us at [email protected]