Emission Spectrometer Data Research Articles

Thermal infrared spectral characteristics of martian dust deposits and evidence for atmosphere-regolith interactions

It has been hypothesized that the dust component of the Martian surface is globally homogeneous, based on chemical similarity between landing sites and spectral similarity from select areas within bright regions. We tested that hypothesis by producing the first near-global data set of surface spectral emissivity (excluding polar regions) across the ∼233–508 and 825–1650 cm−1 (∼20–50 and 6–12 μm) spectral ranges from Mars Global Surveyor Thermal Emission Spectrometer data and using various data reduction techniques to search for any spectral heterogeneity in bright regions that might be present. We found no unequivocal evidence for spectral heterogeneity, supporting the hypothesis that dust is globally homogenized. The global emissivity product permits new spectral parameter maps and preliminary assessments of atmosphere-regolith interactions. We produced the first map of the Christiansen feature (CF) and show that, unlike on the Moon, where CF is a proxy for bulk silica content, CF position on Mars is primarily associated with dust cover. We produced an updated map of the 1630 cm−1 emissivity peak that arises from bound H2O in fine-particulate material and show that the peak is nearly ubiquitous across the Martian surface, including in dark regions with relatively low dust cover. This is attributed to minor amounts of dust disproportionally contributing to the spectral signal in the ∼1630 cm−1 region. We show that regions within the equatorial dust deposits with higher annual modeled frequency of nighttime CO2 frosts are more likely to have lower emissivity in the ∼1350-1400 cm−1 region, consistent with a higher fraction of unconsolidated dust. This provides the first spectral evidence for a previously hypothesized regolith gardening process via a diurnal CO2 cycle, representing an important surface-atmosphere interaction that may contribute to near-surface porosity and affect diffusive exchange of H2O between atmosphere and hydrated solids (ice, minerals) in the regolith.

Mapping Phyllosilicates on the Asteroid Bennu Using Thermal Emission Spectra and Machine Learning Model Applications

AbstractBennu, the target of the OSIRIS‐REx mission, is an asteroid with compositions analogous to low petrologic type CI, CM, CR, and/or ungrouped carbonaceous chondrites. Asteroids like Bennu provide information about the building blocks of the early Solar System. Analysis of the mid‐infrared remote sensing data informs mineral quantification. We apply a phyllosilicate specific model, developed by Breitenfeld et al. (2021, https://doi.org/10.1029/2021je007035) that distinguishes between Mg and Fe serpentines, to Baseball Diamond 1 (BBD1), equatorial station 3 (EQ3), and touch‐and‐go OSIRIS‐REx thermal emission spectrometer data. The average total phyllosilicate predictions are 73 (BBD1) and 72 vol% (EQ3). We observe higher Fe‐cronstedtite and lower Mg‐rich serpentine content in the equatorial region of Bennu than average. Mid‐infrared spectral variability may be explained by sorting effects through mass movement.

Martian Atmospheric Spectral End‐Members Retrieval From ExoMars Thermal Infrared (TIRVIM) Data

AbstractKey knowledge about planetary composition can be recovered from the study of thermal infrared spectral range datasets. This range has a huge diagnostic potential because it contains diagnostic absorptions from a planetary surface and atmosphere. The main goal of this study is to process and interpret the dataset from the Thermal Infrared channel (TIRVIM) which is part of the Atmospheric Chemistry Suite of the ExoMars2016 Trace Gas Orbiter mission to find and characterize dust and water ice clouds in the atmosphere. The method employed here is based on the application of principal component analysis and target transformation techniques to extract the independent variable components present in the analyzed dataset. Spectral shapes of both atmospheric dust and water ice aerosols have been recovered from the analysis of TIRVIM data. The comparison between our results with those previously obtained on Thermal Emission Spectrometer (TES) data and with previous analysis on TIRVIM data, validates the methodology here applied, showing that it allows to correctly recover the atmospheric spectral endmembers present in the TIRVIM data. Moreover, comparison with atmospheric retrievals on PFS, TES and IRIS data, allowed us to assess the temporal stability and homogeneity of dust and water ice components in the Martian atmosphere over a time period of almost 50 years.

Insight Into Formation Processes of Layered Ejecta Craters on Mars From Thermophysical Observations

AbstractUnderstanding the morphological characteristics of craters that are indicative of their formation environment can provide insight into surface geology. Layered ejecta (LE) craters, found on Mars and some other planetary bodies, have been hypothesized to have formed as a result of either interaction with subsurface volatiles (volatile fluidization model) and/or with the atmosphere (atmospheric entrainment model). Formation of LE craters by either model should result in different grain size distributions throughout the ejecta deposit. Using thermal inertia to infer surface properties, we investigated LE craters and their ejecta deposits in an effort to distinguish between possible LE formation processes on Mars. We used thermophysical properties of crater ejecta to determine grain size distribution, to model horizontal mixtures and vertical layering, and to identify materials present within the ejecta. We assessed the thermal properties of 50 uniformly sampled LE craters using Mars Odyssey Thermal Emission Imaging System (THEMIS) and Mars Global Surveyor Thermal Emission Spectrometer (TES) data. Our THEMIS analysis identifies 12 craters with grain size distributions consistent with the volatile fluidization model, 3 craters that have characteristics potentially associated with either model, and 22 craters that do not exhibit characteristics matching either model. Our TES analysis identifies 11 craters with characteristics consistent with the volatile fluidization model and 8 craters that are consistent with the atmospheric entrainment model. While some observations of grain size distributions provide evidence for either or both models, there is not overwhelming support for either model, potentially due to uncertainties of derived thermal inertia data.

Machine Learning Mid‐Infrared Spectral Models for Predicting Modal Mineralogy of CI/CM Chondritic Asteroids and Bennu

AbstractPlanetary surfaces can be complex mixtures of coarse and fine particles that exhibit linear and nonlinear mixing behaviors at mid‐infrared (MIR) wavelengths. Machine learning multivariate analysis can estimate modal mineralogy of mixtures and is favorable because it does not assume linear mixing across wavelengths. We used partial least squares (PLS) and least absolute shrinkage and selection operator (lasso), two types of machine learning, to build MIR spectral models to determine the surface mineralogy of the asteroid (101955) Bennu using OSIRIS‐REx Thermal Emission Spectrometer (OTES) data. We find that PLS models outperform lasso models. The cross‐validated root‐mean‐square error of our final PLS models (consisting of 317 unique spectra of samples derived from 13 analog mineral samples and eight meteorites) range from ∼4 to 13 vol% depending on the mineral group. PLS predictions in vol% of Bennu's average global composition are 78% phyllosilicate, 9% olivine, 11% carbonates, and 6% magnetite. Pyroxene is not predicted for the global average spectrum, though it has been detected in small amounts on Bennu. These mineral abundances confirm previous findings that the composition of Bennu is consistent with CI/CM chondrites with high degrees of aqueous alteration. The predicted mineralogy of two previously identified OTES spectral types vary minimally from the global average. In agreement with previous work, we interpret OTES spectral differences as primarily caused by relative abundances of fine particulates rather than major compositional variations.

Developed split window method to retrieve land surface temperature from HYTES thermal hyperspectral images using genetic algorithm

ABSTRACTThis article aims to establish a new method to retrieve land surface temperature (LST) from hyperspectral thermal emission spectrometer (HYTES) data with split window (SW) algorithm. First, the optimal bands of HYTES sensor were selected with the genetic algorithm and then were used in the SW algorithm. In the SW algorithm, its coefficients were obtained based on several subranges of atmospheric column water vapours (CWVs) and view zenith angle (VZA) under various land surface conditions, in order to remove the atmospheric effect and improve the retrieval accuracy. Results showed that the root-mean-square error (RMSE) varies for different CWV and VZA, and with the increasing CWV and VZA, the RMSE value also increases. The emissivity, CWV, and VZA were also obtained for pixels. The sensitive analysis of LST retrieval to instrument noise and uncertainty of pixel emissivity and water vapour demonstrated the good performance of the proposed algorithm. Finally, the new algorithm was applied to HYTES sensor data, and the LST was validated using LST product of HYTES sensor obtained by NASA. The results showed that the RMSE of the LST retrieval with the proposed algorithm and the LST product of sensor for data 1 and data 2 is 1.3 K and 1.6 K, respectively.

Synchrotron emission in molecular cloud cores: the SKA view

Understanding the role of magnetic fields in star-forming regions is of fundamental importance. In the near future, the exceptional sensitivity of the Square Kilometre Array (SKA) will offer a unique opportunity to evaluate the magnetic field strength in molecular clouds and cloud cores through synchrotron emission observations. The most recent Voyager 1 data, together with Galactic synchrotron emission and Alpha Magnetic Spectrometer data, constrain the flux of interstellar cosmic-ray electrons between ∼3 MeV and ∼832 GeV, in particular in the energy range relevant for synchrotron emission in molecular cloud cores at SKA frequencies. Synchrotron radiation is entirely due to primary cosmic-ray electrons, the relativistic flux of secondary leptons being completely negligible. We explore the capability of SKA in detecting synchrotron emission in two starless molecular cloud cores in the southern hemisphere, B68 and FeSt 1-457, and we find that it will be possible to reach signal-to-noise ratios of the order of 2 − 23 at the lowest frequencies observable by SKA (60 − 218 MHz) with one hour of integration.

MGS‐TES Spectra Suggest a Basaltic Component in the Regolith of Phobos

AbstractThe origins of the Martian moons Phobos and Deimos have been the subjects of considerable debate. Visible and near‐infrared spectra of these bodies are dark and nearly featureless, with red slopes of varying degrees. These spectra are generally consistent with those of carbonaceous asteroids, leading to the hypothesis that Phobos and Deimos are captured carbonaceous asteroids. The shapes and inclinations of the orbits of Phobos and Deimos present problems for the asteroid capture hypothesis. This had led researchers to suggest that Phobos and Deimos coaccreted with Mars or that they are the result of an impact with Mars or in the Mars vicinity. In this work, we reexamine Mars Global Surveyor Thermal Emission Spectrometer (MGS‐TES) data of Phobos and compare spectra of the Phobos surface to mid‐IR spectra of the ungrouped C2 meteorite Tagish Lake (a suggested analog for D‐class asteroids) and particulate basalt and phyllosilicate samples (mixed with carbon black to reduce their visible albedos) acquired in a simulated airless body environment. We find that Tagish Lake is a poor mid‐IR spectral analog to Phobos and that major spectral features in the Phobos spectrum are best matched by a silicate transparency feature similar to that found for finely particulate basalt. Other features in the spectrum are likely best explained by a phyllosilicate component. We suggest that these results indicate that at a portion of the Phobos surface regolith is derived from the Martian crust.

Application of high gradient magnetic separation for oil remediation using polymer-coated magnetic nanoparticles

Abstract Oil can be released into the environment from different sources such as runoff, accidental oil spills and oily wastewater discharges produced during industrial activities and can have dramatic impacts on the environment. The limitations of current clean-up techniques have inspired researchers to study the application of nanotechnology for oil remediation. Previously, we reported excellent oil-removal efficiency of a reference MC252 oil using polyvinylpyrrolidone (PVP)-coated magnetic nanoparticles (NPs) from an oil-water mixture under a wide range of environmentally relevant conditions. In the current report, the same type of NPs were used with a high gradient magnetic separation (HGMS) technique for the rapid removal of oil from oil-water mixtures in a continuous flow system. Using a high magnetic field (0.56 T) and 1 h mixing time, fluorescence and inductively coupled plasma-optical emission spectrometer (ICP-OES) data showed approximately 85–95% oil and NP removal under all conditions. Gas chromatography–mass spectrometry (GC–MS) results show 88 and near 100% removal of alkanes (C9-C22) for experiments in the presence or absence of stainless steel wool, respectively. Continuous use over 7 h of operation (17 L oil-water mixture was treated) showed no reduction in oil and NP removal capacity. Results showed that increasing the magnetic field and inserting stainless steel wool significantly increased oil and NP removal efficiencies. This study shows that using HGMS is a promising technique for oil remediation using PVP-coated magnetic NPs.

Martian polar vortices: Comparison of reanalyses

AbstractThe structure and evolution of the Martian polar vortices is examined using two recently available reanalysis systems: version 1.0 of the Mars Analysis Correction Data Assimilation (MACDA) and a preliminary version of the Ensemble Mars Atmosphere Reanalysis System (EMARS). There is quantitative agreement between the reanalyses in the lower atmosphere, where Mars Global Surveyor (MGS) Thermal Emission Spectrometer (TES) data are assimilated, but there are differences at higher altitudes reflecting differences in the free‐running general circulation model simulations used in the two reanalyses. The reanalyses show similar potential vorticity (PV) structure of the vortices: There is near‐uniform small PV equatorward of the core of the westerly jet, steep meridional PV gradients on the polar side of the jet core, and a maximum of PV located off of the pole. In maps of 30 sol mean PV, there is a near‐continuous elliptical ring of high PV with roughly constant shape and longitudinal orientation from fall to spring. However, the shape and orientation of the vortex varies on daily time scales, and there is not a continuous ring of PV but rather a series of smaller scale coherent regions of high PV. The PV structure of the Martian polar vortices is, as has been reported before, very different from that of Earth's stratospheric polar vortices, but there are similarities with Earth's tropospheric vortices which also occur at the edge of the Hadley Cell, and have near‐uniform small PV equatorward of the jet, and a large increase of PV poleward of the jet due to increased stratification.

Integrated visible and near-infrared, shortwave infrared, and longwave infrared full-range hyperspectral data analysis for geologic mapping

Airborne visible/infrared imaging spectrometer (AVIRIS) and spatially coincident hyperspectral thermal emission spectrometer (HyTES) data were used to map geology and alteration for a site in northern Death Valley, California and Nevada. AVIRIS with 224 bands from 0.4 to 2.5 μ m were converted to reflectance. HyTES data with 256 bands covering 8 to 12 μ m were converted to emissivity. Two approaches were investigated for integration of the datasets for full spectrum analysis. A combined (integrated) bands method utilized 332 spectral bands spanning both datasets. Spectral endmembers were extracted, and the predominant material at each pixel was mapped for the full spectral range using partial unmixing. This approach separated a variety of materials, but it was difficult to directly relate mapping results to surface properties. The second method used visible to near-infrared, shortwave infrared, and longwave infrared data independently to determine and map key endmembers in each spectral range. AVIRIS directly mapped a variety of specific minerals, while HyTES separated and mapped several igneous rock phases. Individual mapping results were then combined using geologically directed logical operators. The full-range results illustrate that integrated analysis provides advantages over use of just one spectral range, leading to improved understanding of the distribution of geologic units and alteration.

Compositional provinces of Mars from statistical analyses of TES, GRS, OMEGA and CRISM data

AbstractWe identified 10 distinct classes of mineral assemblage on Mars through statistical analyses of mineral abundances derived from Mars Global Surveyor Thermal Emission Spectrometer (TES) data at a spatial resolution of 8 pixels per degree. Two classes are new regions in Sinus Meridiani and northern Hellas basin. Except for crystalline hematite abundance, Sinus Meridiani exhibits compositional characteristics similar to Meridiani Planum; these two regions may share part of a common history. The northern margin of Hellas basin lacks olivine and high‐Ca pyroxene compared to terrains just outside the Hellas outer ring; this may reflect a difference in crustal compositions and/or aqueous alteration. Hesperian highland volcanic terrains are largely mapped into one class. These terrains exhibit low‐to‐intermediate potassium and thorium concentrations (from Gamma Ray Spectrometer (GRS) data) compared to older highland terrains, indicating differences in the complexity of processes affecting mantle melts between these different‐aged terrains. A previously reported, locally observed trend toward decreasing proportions of low‐calcium pyroxene relative to total pyroxene with time is also apparent over the larger scales of our study. Spatial trends in olivine and pyroxene abundance are consistent with those observed in near‐infrared data sets. Generally, regions that are distinct in TES data also exhibit distinct elemental characteristics in GRS data, suggesting that surficial coatings are not the primary control on TES mineralogical variations, but rather reflect regional differences in igneous and large‐scale sedimentary/glacial processes. Distinct compositions measured over large, low‐dust regions from multiple data sets indicate that global homogenization of unconsolidated surface materials has not occurred.

Variability of the martian seasonal CO2 cap extent over eight Mars Years

We present eight Mars Years of nearly continuous tracking of the CO2 seasonal cap edges from Mars Year (MY) 24 to 31 using Mars Global Surveyor (MGS) Thermal Emission Spectrometer (TES) and Mars Reconnaissance Orbiter (MRO) Mars Climate Sounder (MCS) thermal infrared data. Spatial and temporal resolutions are 1 pixel per degree and 10°Ls (aerocentric longitude of the Sun). The seasonal caps are defined as the regions where the diurnal radiometric temperature variations at ∼32μm wavelength do not exceed 5K. With this definition, terrains with small areal fraction of defrosted regolith able to experience measurable diurnal temperature cycles are not mapped as part of the cap. This technique is adequate to distinguish CO2 from H2O ices, and effective during the polar night or under low illumination conditions. The present analysis answers outstanding questions stemming from fragmented observations at visible wavelengths: (1) the previously sparsely documented growth of the North seasonal caps (160°<Ls<270°) is shown to be repeatable within 1–2° equivalent latitude, and monotonic over the MY 24–31 time period; high repeatability is observed during the retreat of the caps in non-dusty years (∼1° or less equivalent latitude); (2) the MY 25 storm does not seem to have impacted the growth rate, maximal extents, or recession rate of the North seasonal caps, whereas the MY 28 dust storm clearly sped up the recession of the cap (∼2° smaller on average after the storm, during the recession, compared to other years); (3) during non-dusty years, the growth of the South seasonal cap (350°<Ls<100°) presents noticeable variability (up to ∼4° equivalent latitude near Ls=20°) with a maximum extent reached near Ls=90°; (4) the retreat of the Southern seasonal cap (100°<Ls<310°) exhibits large inter-annual variability, especially near 190°<Ls<220°; (5) the recession of the MY 25 South seasonal cap is significantly accelerated during the equinox global dust storm, with surface temperatures suggesting increased patchiness or enhanced dust mantling on the CO2 ice. These results suggest that atmospheric temperatures and dust loading are the primary source of variability in an otherwise remarkably repeatable cycle of seasonal cap growth and recession.

The seasonal cycle of water vapour on Mars from assimilation of Thermal Emission Spectrometer data

We present for the first time an assimilation of Thermal Emission Spectrometer (TES) water vapour column data into a Mars global climate model (MGCM). We discuss the seasonal cycle of water vapour, the processes responsible for the observed water vapour distribution, and the cross-hemispheric water transport. The assimilation scheme is shown to be robust in producing consistent reanalyses, and the global water vapour column error is reduced to around 2–4prμm depending on season. Wave activity is shown to play an important role in the water vapour distribution, with topographically steered flows around the Hellas and Argyre basins acting to increase transport in these regions in all seasons. At high northern latitudes, zonal wavenumber 1 and 2 stationary waves during northern summer are responsible for spreading the sublimed water vapour away from the pole. Transport by the zonal wavenumber 2 waves occurs primarily to the west of Tharsis and Arabia Terra and, combined with the effects of western boundary currents, this leads to peak water vapour column abundances here as observed by numerous spacecraft. A net transport of water to the northern hemisphere over the course of one Mars year is calculated, primarily because of the large northwards flux of water vapour which occurs during the local dust storm around LS=240–260°. Finally, outlying frost deposits that surround the north polar cap are shown to be important in creating the peak water vapour column abundances observed during northern summer.

Similarity ratio analysis for early stage fault detection with optical emission spectrometer in plasma etching process.

A Similarity Ratio Analysis (SRA) method is proposed for early-stage Fault Detection (FD) in plasma etching processes using real-time Optical Emission Spectrometer (OES) data as input. The SRA method can help to realise a highly precise control system by detecting abnormal etch-rate faults in real-time during an etching process. The method processes spectrum scans at successive time points and uses a windowing mechanism over the time series to alleviate problems with timing uncertainties due to process shift from one process run to another. A SRA library is first built to capture features of a healthy etching process. By comparing with the SRA library, a Similarity Ratio (SR) statistic is then calculated for each spectrum scan as the monitored process progresses. A fault detection mechanism, named 3-Warning-1-Alarm (3W1A), takes the SR values as inputs and triggers a system alarm when certain conditions are satisfied. This design reduces the chance of false alarm, and provides a reliable fault reporting service. The SRA method is demonstrated on a real semiconductor manufacturing dataset. The effectiveness of SRA-based fault detection is evaluated using a time-series SR test and also using a post-process SR test. The time-series SR provides an early-stage fault detection service, so less energy and materials will be wasted by faulty processing. The post-process SR provides a fault detection service with higher reliability than the time-series SR, but with fault testing conducted only after each process run completes.

Compositional evolution of lava plains in the Syria-Thaumasia Block, Mars

Tharsis is the most prominent volcanic province on Mars, yet the compositions of lava flows and how composition relates to the development of Tharsis are poorly known. Most of Tharsis is covered with air-fall dust, which inhibits spectroscopic determination of lava mineralogy. The Syria-Thaumasia Block (STB) is a complex tectono-volcanic province closely related to the Tharsis bulge. The lava plains of STB have different emplacement ages, which provide an opportunity to examine whether magma composition changed with the evolution of Tharsis. In this study, we assessed the lava plains using Thermal Emission Spectrometer (TES) data. Using derived physical properties, we targeted dust-free regions from four different-aged geological units surfaces and determined the mineralogical composition by modeling the average TES surface spectrum from each of the four surfaces. All units have similar mineralogy but the younger two units have elevated abundance of high-SiO2 phases. The spatial distribution of wrinkle ridges indicates lava plains of unit HNr (older ridged plains material) and Hr (younger ridged plains material) were emplaced before the rise of Tharsis, whereas Hsl (flows of lower member) and Hsu (upper member) were emplaced after Tharsis uplift was initiated. We show that the magma composition differed in the lava plains of STB after the uplift of Tharsis. This study further characterizes early martian magma composition and evolution.

Deriving chemical trends from thermal infrared spectra of weathered basalt: Implications for remotely determining chemical trends on Mars

Variations in chemical composition over a planetary surface can be used to study petrologic and aqueous alteration processes. The desire for such data on Mars has prompted investigators to derive chemistry from models of Thermal Emission Spectrometer data. Although chemistry derived from thermal infrared spectral models is reportedly reliable for unaltered igneous rocks, the martian surface has experienced chemical weathering, which can adversely affect models. Here, we examine weathered basalts from Baynton, Australia, for which chemical weathering trends have been previously characterized, to test how well chemistry and chemical trends can be determined from TIR spectra of weathered rocks. The mineralogy of variably weathered rocks was derived from TIR spectra by linear mixing, and major-element chemistry was calculated from those mineral models. Derived chemistries and trends were compared to those measured by X-ray fluorescence. TIR spectroscopy is sensitive to weathering products in weathering rinds because the products are present in a coating geometry, making it a useful technique for remotely detecting weathered surfaces on planetary surfaces such as Mars. This sensitivity results in significant modeled abundances of weathering products (>80% of all phases) from TIR spectra of weathered Baynton surfaces, despite evidence from microscopy and X-ray diffraction showing that igneous minerals dominate the weathering rind. Measured chemical weathering trends show loss of MgO, CaO, Na2O, and K2O and relative enrichment in Al2O3 and FeOT. The modeled trends are similar to the measured trends, but a closer look at the modeled oxide abundances demonstrates that most oxides (i.e., alkalis, SiO2, and FeOT) are not well modeled, especially for weathered surfaces. The reasons for this are: (1) non-linear mixing and the presence of secondary coatings causes the overestimation of secondary phases in spectral models, and (2) spectral libraries generally lack poorly crystalline and amorphous secondary phases that are common in weathering rinds so that crystalline phases such as phyllosilicates are selected. The martian surface has likely been weathered less pervasively than the Baynton rocks and, therefore, weathering products may be dominated by poorly crystalline and amorphous phases, rather than crystalline phyllosilicates. Adding these phases to spectral libraries could improve bulk chemistry derived from the martian surface; however, if the secondary phases are present in a coating geometry, the derived chemistry will reflect the composition of the coating, and it may be difficult to infer the chemistry of the parent rock.

Allophane detection on Mars with Thermal Emission Spectrometer data and implications for regional-scale chemical weathering processes

Models of Thermal Emission Spectrometer (TES) data suggest that poorly-crystalline weathering products allophane and aluminosilicate gel occur in several low-albedo regions of Mars. The presence of allophane in TES models indicates that the martian surface experienced low-temperature chemical weathering at low water-to-rock ratios and mildly acidic to neutral pH on regional scales. The allophane and gel may be ancient and preserved by a persistently dry martian climate. Alternatively, evidence for recent ground ice in these regions suggests that pedogenic processes causing the formation of poorly-crystalline aluminosilicates could be late Amazonian in age and may be active today. While previous models have suggested that global-scale acidic weathering has occurred on Mars for the past 3.5 billion years, the presence of allophane indicates that acidic weathering was not occurring in these low-albedo regions and that mildly acidic to neutral weathering has been an important regional-scale weathering process on the martian surface.

The influence of local topography for wind direction on Mars: two examples of dune fields in crater basins

ABSTRACTIn this work, we perform an analysis of large dark dunes within Moreux Crater and Herschel Crater on Mars using High Resolution Imaging Science Experiment (HiRISE) and Context Camera (CTX) data sets. These data allow us to conduct a detailed analysis of dune morphology and slip faces, concluding that the studied dune fields are influenced by topographically‐controlled complex wind directions. Our morphological analysis reveals that inside Moreux Crater in particular, the topographic setting dominates the wind flow direction, leading to the development of a sand transport pathway encircling the central peak of the crater. The dune fields in Herschel Crater are also affected by winds controlled by variable topography as suggested by the presence of complex dunes and dune fields. Our analysis indicate that the studied dune systems is not the result of paleo‐wind regimes. Furthermore, we perform thermal inertia measurements using thermal emission spectrometer (TES) data, which indicate that the studied dune fields consist of medium sand 250–500 µm in diameter. Copyright © 2012 John Wiley &amp; Sons, Ltd.

Martian water ice clouds: A view from Mars Global Surveyor Thermal Emission Spectrometer

[1] We have used the Mars Global Surveyor Thermal Emission Spectrometer (MGS TES) data to map water ice clouds in the Martian atmosphere in the latitude range –60 to +60 over a period of three Martian years. We have used the same method we have previously used on Viking Infrared Thermal Mapper data in order to allow direct comparison of the cloud behavior in the Viking and MGS eras and confirmed the validity of this method by comparing it to MGS TES standard retrievals. We note that the large-scale behavior of water ice clouds is remarkably consistent, both between the Viking and the MGS eras as well as between years observed by MGS. We also compare our results to water ice absorption-only optical depths derived from TES data and show that correlation is best for type 2 water ice clouds.