•We find that the lunar Christiansen Feature is influenced by space weathering.•Albedo-dependent thermal gradients are the likely cause of the observed effect.•Composition is also demonstrated to ...influence the Christiansen Feature.•Space weathering can be partly removed from Diviner data using an independent maturity index.
Multispectral infrared measurements by the Diviner Lunar Radiometer Experiment on the Lunar Renaissance Orbiter enable the characterization of the position of the Christiansen Feature, a thermal infrared spectral feature that laboratory work has shown is proportional to the bulk silica content of lunar surface materials. Diviner measurements show that the position of this feature is also influenced by the changes in optical and physical properties of the lunar surface with exposure to space, the process known as space weathering. Large rayed craters and lunar swirls show corresponding Christiansen Feature anomalies. The space weathering effect is likely due to differences in thermal gradients in the optical surface imposed by the space weathering control of albedo. However, inspected at high resolution, locations with extreme compositions and Christiansen Feature wavelength positions – silica-rich and olivine-rich areas – do not have extreme albedos, and fall off the albedo- Christiansen Feature wavelength position trend occupied by most of the Moon. These areas demonstrate that the Christiansen Feature wavelength position contains compositional information and is not solely dictated by albedo. An optical maturity parameter derived from near-IR measurements is used to partly correct Diviner data for space weathering influences.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK, ZRSKP
Chloride salt‐bearing deposits on Mars were discovered using the Mars Odyssey Thermal Emission Imaging System (THEMIS) and have been characterized by both mid‐infrared (MIR) and ...visible‐to‐near‐infrared (VNIR) remote sensing instruments. The chloride salt‐bearing deposits exhibit a blue slope at MIR wavelengths and a featureless red slope at VNIR wavelengths. These deposits also lack strong 3 µm bands in VNIR spectra, indicating that they are desiccated compared to the surrounding regolith. The lack of VNIR spectral features suggests that an anhydrous chloride salt, the most likely of which is halite, is responsible for the observed spectral slope. In this work, we use laboratory spectra and a hybrid T‐matrix/Hapke light scattering model to constrain the particle sizes and salt abundances of the Martian chloride salt‐bearing deposits. Our work shows that the two broad spectral classes of these deposits observed by THEMIS can be explained by a difference in the particle size of the admixed silicate regolith. In all cases, chloride salt abundances of 10–25% are required to match the THEMIS data. The chloride salt abundances determined in this work suggest deposition in a lacustrine/playa setting or in association with late‐stage groundwater upwelling.
Key Points
Laboratory spectra and scattering models confirm the presence of chloride salt deposits on Mars
THEMIS spectra of salt deposits are consistent with the presence of approximately 10–25 wt % halite
Salts were deposited in either a lacustrine/playa setting or by late‐stage groundwater upwelling
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BFBNIB, FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SAZU, SBCE, SBMB, UL, UM, UPUK
Plagioclase feldspar is the most abundant rock‐forming mineral in the crust of the Earth, Moon, and Mars and is also an important component in some minor bodies in the Solar System. The distribution, ...abundance, and precise composition of plagioclase on planetary surfaces from remote sensing data are important measurements for evaluating changing conditions during magma evolution. Optical constants are critical input parameters in radiative transfer theory, which enables modeling of spectra for the extraction of mineral abundances and grain sizes from a remotely sensed spectrum. Mid‐infrared (MIR) optical constants of most triclinic rock‐forming minerals are not available due to the complexity associated with the derivation of optical constants of low‐symmetry minerals. In this work, we have calculated the MIR optical constants of a labradorite single crystal using dispersion theory and laboratory reflectance spectra at non‐normal incidence. The optical constants we derived here will assist in modeling spectra in the MIR region and quantifying mineral composition, particle size, and abundances from remote sensing data.
Key Points
Mid‐infrared spectroscopy is an effective tool to detect plagioclase from remote sensing data sets
We have derived the mid‐infrared oriented optical constants of a triclinic rock‐forming plagioclase mineral, labradorite
The averaged optical constants acquired from contributions of each principal axis can be used to model spectra by radiative transfer theory
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FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SAZU, SBCE, SBMB, UL, UM, UPUK
The Mairan domes are four features located in northern Oceanus Procellarum at ∼312.3E, 41.4N on the Moon. High resolution visible imagery, visible‐to‐mid‐IR spectra, and Lunar Prospector Th abundance ...data all indicate that these four domes have a composition that is consistent with derivation from a Si‐rich, highly evolved magma.
Key Points
The Mairan domes are silicic volcanic constructs
Their formation requires either liquid immiscibility or basaltic underplating
These volcanoes are prime targets for future lunar exploration
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FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SAZU, SBCE, SBMB, UL, UM, UPUK
Radiative transfer models of remotely acquired infrared spectra result in quantitative identification of minerals on planetary surfaces. Optical constants, or the real (n) and imaginary (k) indices ...of refraction are necessary inputs in such models. Pyroxenes are ubiquitous on the surfaces of terrestrial bodies within our solar system and can be readily used as thermo‐barometers to interpret magmatic histories. However, optical constants for intermediate pyroxene compositions are undetermined. Here, we have determined the optical constants of two natural orthopyroxenes both in the visible/near‐infrared (VNIR) and mid‐infrared (MIR) regions. VNIR reflectance spectra were measured using powdered samples and modeled using a combination of Hapke theory and Kramers‐Kronig analysis. MIR reflectance spectra were measured on oriented single crystal samples with non‐normal incidence and modeled using Lorentz‐Lorenz dispersion theory. The optical constants derived here are available to the scientific community at https://doi.org/10.5281/zenodo.4758045 to be used in the interpretation of remote sensing data.
Key Points
Optical constants are necessary inputs into remote sensing models that quantitatively determine modal mineralogies on planetary surfaces
Many optical constants available are end member compositon only
Here we calculate the optical constants for two compositions of orthopyroxene, common minerals observed on planetary surfaces, in the visible/near infrared and mid to far infrared
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FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SAZU, SBCE, SBMB, UL, UM, UPUK
Arsenic is present in numerous ecosystems and microorganisms have developed various mechanisms to live in such hostile environments. Herminiimonas arsenicoxydans, a bacterium isolated from arsenic ...contaminated sludge, has acquired remarkable capabilities to cope with arsenic. In particular our previous studies have suggested the existence of a temporal induction of arsenite oxidase, a key enzyme in arsenic metabolism, in the presence of As(III).
Microarrays were designed to compare gene transcription profiles under a temporal As(III) exposure. Transcriptome kinetic analysis demonstrated the existence of two phases in arsenic response. The expression of approximatively 14% of the whole genome was significantly affected by an As(III) early stress and 4% by an As(III) late exposure. The early response was characterized by arsenic resistance, oxidative stress, chaperone synthesis and sulfur metabolism. The late response was characterized by arsenic metabolism and associated mechanisms such as phosphate transport and motility. The major metabolic changes were confirmed by chemical, transcriptional, physiological and biochemical experiments. These early and late responses were defined as general stress response and specific response to As(III), respectively.
Gene expression patterns suggest that the exposure to As(III) induces an acute response to rapidly minimize the immediate effects of As(III). Upon a longer arsenic exposure, a broad metabolic response was induced. These data allowed to propose for the first time a kinetic model of the As(III) response in bacteria.
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DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
Both the speciation and toxicity of arsenic are affected by bacterial transformations, i.e. oxidation, reduction or methylation. These transformations have a major impact on environmental ...contamination and more particularly on arsenic contamination of drinking water. Herminiimonas arsenicoxydans has been isolated from an arsenic- contaminated environment and has developed various mechanisms for coping with arsenic, including the oxidation of As(III) to As(V) as a detoxification mechanism.
In the present study, a differential transcriptome analysis was used to identify genes, including arsenite oxidase encoding genes, involved in the response of H. arsenicoxydans to As(III). To get insight into the molecular mechanisms of this enzyme activity, a Tn5 transposon mutagenesis was performed. Transposon insertions resulting in a lack of arsenite oxidase activity disrupted aoxR and aoxS genes, showing that the aox operon transcription is regulated by the AoxRS two-component system. Remarkably, transposon insertions were also identified in rpoN coding for the alternative N sigma factor (sigma54) of RNA polymerase and in dnaJ coding for the Hsp70 co-chaperone. Western blotting with anti-AoxB antibodies and quantitative RT-PCR experiments allowed us to demonstrate that the rpoN and dnaJ gene products are involved in the control of arsenite oxidase gene expression. Finally, the transcriptional start site of the aoxAB operon was determined using rapid amplification of cDNA ends (RACE) and a putative -12/-24 sigma54-dependent promoter motif was identified upstream of aoxAB coding sequences.
These results reveal the existence of novel molecular regulatory processes governing arsenite oxidase expression in H. arsenicoxydans. These data are summarized in a model that functionally integrates arsenite oxidation in the adaptive response to As(III) in this microorganism.
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DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
Since biofilms are an important issue in the fields of medicine and health, several recent microbiological studies have focused on their formation and their contribution to toxic compound resistance ...mechanisms. In this review, we describe how metals impact biofilm formation and resistance, and how biofilms can help cells resist toxic metals. First, the organic matrix acts as a barrier isolating the cells from many environmental stresses. Secondly, the metabolism of the cells changes, and a slowly-growing or non-growing sub-population of cells known as persisters emerges. Thirdly, in the case of multispecies biofilms, metabolic interactions are developed, allowing cells to be more persistent or to have greater capacity to survive than a single species biofilm. Finally, we discuss how the high density of the cells may promote horizontal gene transfer processes, resulting in the acquisition of new features. All these crucial mechanisms enable microorganisms to survive and colonize toxic environments, and probably accelerate ongoing evolutionary processes.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
After the publication of our article 1, similarities between lanes 2, 5 and 6 (aoxB-, rpoN- and dnaJ-) and between lanes 3 and 4 (aoxR- and aoxS-) in Fig. 4 were brought to our attention. This error ...occurred during the compilation of the Western blot images. A corrected version of Fig. 4 has been assembled from the original Western blot experiments and is presented below. This error affects neither the other results nor the conclusions of the article. Fig. 4 Immunodetection of AoxB protein in total protein extracts of H. arsenicoxydans wild-type and mutant strains
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DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
•2D elastic-scattering patterns of single particles.•Orientation control of optically trapped particles.•Comparison with diffraction calculations.
We demonstrate a method for recording 2D ...forward-scattering patterns from optically trapped single airborne particles at multiple angular orientations. We collected images of trapped particles simultaneously with their scattering patterns to observe changes in the patterns with orientation. We present measurements of particles with wide-ranging morphologies from nearly spherical to highly irregular and with various compositions. The highly irregularly shaped particles have scattering patterns with spots of high intensity whose locations change with particle orientation. Additionally, measurements of a manufactured polystyrene spheroid of a known size are compared with calculated diffraction patterns. Such controlled-orientation measurements have the potential to help develop algorithms to characterize airborne aerosol particles using morphological information inferred from remote-sensing or other elastic light scattering measurements.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
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