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A laboratory study was performed using the Visible Oxford Space Environment Goniometer in which the broadband (350–1250 nm) bidirectional reflectance distribution functions (BRDFs) of two representative Apollo regolith samples were measured, for two surface roughness profiles, across a range of viewing angles—reflectance: 0–70°, in steps of 5°; incidence: 15°, 30°, 45°, and 60°; and azimuthal: 0°, 45°, 90°, 135°, and 180°. The BRDF datasets were fitted using the Hapke BRDF model to (1) provide a method of comparison to other photometric studies of the lunar regolith and (2) to produce Hapke parameter values which can be used to extrapolate the BRDF to all angles. Importantly, the surface profiles of the samples were characterized using an Alicona 3D® instrument, allowing two of the free parameters within the Hapke model, φ and θ¯, which represent porosity and surface roughness, respectively, to be constrained. The study determined that, for θ¯, the 500–1000 μm size‐scale is the most relevant for the BRDF. Thus, it deduced the following "best fit" Hapke parameters for each of the samples: Apollo 11 rough—w = 0.315 ± 0.021, b = 0.261 ± 0.007, and hS = 0.039 ± 0.005 (with θ¯ = 21.28° and φ = 0.41 ± 0.02); Apollo 11 smooth—w = 0.281 ± 0.028, b = 0.238 ± 0.008, and hS = 0.032 ± 0.006 (with θ¯ = 13.80° and φ = 0.60 ± 0.02); Apollo 16 rough—w = 0.485 ± 0.155, b = 0.155 ± 0.083, and hS = 0.135 ± 0.007 (with θ¯ = 21.69° and φ = 0.55 ± 0.02); Apollo 16 smooth—w = 0.388 ± 0.057, b = 0.063 ± 0.033, and hS = 0.221 ± 0.011 (with θ¯ = 14.27° and φ = 0.40 ± 0.02). Finally, updated hemispheric albedo functions were determined for the samples, which can be used to set laboratory measured visible scattering functions within thermal models. [ABSTRACT FROM AUTHOR]

On the microscale, the Winchcombe CM carbonaceous chondrite contains a number of lithological units with a variety of degrees of aqueous alteration. However, an understanding of the average hydration state is useful when comparing to other meteorites and remote observations of airless bodies. We report correlated bulk analyses on multiple subsamples of the Winchcombe meteorite, determining an average phyllosilicate fraction petrologic type of 1.2 and an average water content of 11.9 wt%. We show the elemental composition and distribution of iron and iron oxidation state are consistent with measurements from other CM chondrites; however, Winchcombe shows a low Hg concentration of 58.1 ± 0.5 ng g−1. We demonstrate that infrared reflectance spectra of Winchcombe are consistent with its bulk modal mineralogy, and comparable to other CM chondrites with similar average petrologic types. Finally, we also evaluate whether spectral parameters can estimate H/Si ratios and water abundances, finding generally spectral parameters underestimate water abundance compared to measured values. [ABSTRACT FROM AUTHOR]

A laboratory study was performed using the Visible Oxford Space Environment Goniometer in which the broadband (350–1250 nm) bidirectional reflectance distribution function (BRDF) of the Winchcombe meteorite was measured, across a range of viewing angles—reflectance: 0°–70°, in steps of 5°; incidence: 15°, 30°, 45°, and 60°; and azimuthal: 0°, 90°, and 180°. The BRDF dataset was fitted using the Hapke BRDF model to (1) provide a method of comparison to other meteorites and asteroids, and (2) to produce Hapke parameter values that can be used to extrapolate the BRDF to all angles. The study deduced the following Hapke parameters for Winchcombe: w = 0.152 ± 0.030, b = 0.633 ± 0.064, and hS = 0.016 ± 0.008, demonstrating that it has a similar w value to Tagish Lake (0.157 ± 0.020) and a similar b value to Orgueil (0.671 ± 0.090). Importantly, the surface profile of the sample was characterized using an Alicona 3D® instrument, allowing two of the free parameters within the Hapke model φ and θ¯, which represent porosity and surface roughness, respectively, to be constrained as φ = 0.649 ± 0.023 and θ¯ = 16.113° (at 500 μm size scale). This work serves as part of the characterization process for Winchcombe and provides a reference photometry dataset for current and future asteroid missions. [ABSTRACT FROM AUTHOR]

Author(s): J. A. Towbin (corresponding author) [1, 2]; N. E. Bowles [1] Congestive heart failure (CHF) resulting from cardiomyopathy is a serious malady and a principal cause of death and [...]

The highly hydrated, petrologic type 1 CM and CI carbonaceous chondrites likely derived from primitive, water‐rich asteroids, two of which are the targets for JAXA's Hayabusa2 and NASA's OSIRIS‐REx missions. We have collected visible and near‐infrared (VNIR) and mid infrared (MIR) reflectance spectra from well‐characterized CM1/2, CM1, and CI1 chondrites and identified trends related to their mineralogy and degree of secondary processing. The spectral slope between 0.65 and 1.05 μm decreases with increasing total phyllosilicate abundance and increasing magnetite abundance, both of which are associated with more extensive aqueous alteration. Furthermore, features at ~3 μm shift from centers near 2.80 μm in the intermediately altered CM1/2 chondrites to near 2.73 μm in the highly altered CM1 chondrites. The Christiansen features (CF) and the transparency features shift to shorter wavelengths as the phyllosilicate composition of the meteorites becomes more Mg‐rich, which occurs as aqueous alteration proceeds. Spectra also show a feature near 6 μm, which is related to the presence of phyllosilicates, but is not a reliable parameter for estimating the degree of aqueous alteration. The observed trends can be used to estimate the surface mineralogy and the degree of aqueous alteration in remote observations of asteroids. For example, (1) Ceres has a sharp feature near 2.72 μm, which is similar in both position and shape to the same feature in the spectra of the highly altered CM1 MIL 05137, suggesting abundant Mg‐rich phyllosilicates on the surface. Notably, both OSIRIS‐REx and Hayabusa2 have onboard instruments which cover the VNIR and MIR wavelength ranges, so the results presented here will help in corroborating initial results from Bennu and Ryugu. [ABSTRACT FROM AUTHOR]

Introduction: The Winchcombe fall was observed on the 28th of February 2021 and ~600 g of meteoritic material was recovered over the following month [1]. Winchcombe is classified as a CM2 chondrite, though several lithologies are represented in the recovered material showing variations in petrologic type and degree of aqueous alteration. Analyses have been performed to gain a comprehensive understanding of its bulk material properties as part of a nationwide collaboration [e.g. 1, 2]. Here we discuss spectral analyses conducted at the Planetary Spectroscopy Facility at the University of Oxford. These measurements include visible to near-infrared (VNIR; 0.7-5 um) and mid-infrared (MIR; 5-25 um) reflectance measurements of two Winchcombe samples, as well as multi-angle VNIR Bidirectional Reflectance Distribution Function (BRDF) measurements made using the Visible Oxford Space Environment Goniometer [3]. The BRDF was measured for a powdered sample characterized in terms of porosity and surface roughness, and this dataset was used to determine the broadband albedo (0.35-1.25 um) of Winchcombe in [1]. IR Spectroscopy: Reflectance spectra of two samples (BM.2022,M1-91; BM.2022,M2-41) were measured with a Bruker VERTEX 70v Fourier Transform Infrared spectrometer, using a diffuse reflectance accessory under vacuum (~2 hPa) at 4 cm-1 resolution and an average of 150 scans calibrated to a diffuse gold target. The shortest wavelength range (0.8-2 μm) was acquired using an InGaAs detector coupled with a VIS/Quartz beamsplitter, while a RTDLaTGS detector and wide range beamsplitter were used for the near- and mid-infrared (2-25 μm). We correlate the spectra with modal mineralogy as determined using position-sensitive-detector X-ray diffraction (PSD-XRD) [1] and water abundance using thermogravimetric analysis (TGA) [2] for the same samples. A strong feature near 2.7 μm is attributed to OH-stretching, which indicates the aqueously altered mineralogy of the meteorite. It can also be affected by terrestrial alteration products and adsorbed water. Several studies [4,5,6] have used reflectance near this feature to estimate water content of asteroids and meteorites. We compared water abundances as measured through TGA to calculated water abundance using reflectance parameters and found reflectance measurements generally underestimated measured water abundance. The Christiansen feature (reflectance minimum) is located near 9 μm and indicates poor silicate polymerization. The shift in position between the two Winchcombe spectra (~0.1 um) correlates to slightly different olivine contents. The positions in the Winchcombe spectra are consistent with spectra of other CM chondrites [e.g. 7]. The transparency feature (reflectance maximum) near 11.5 um is another compositional indicator and has been shown to correlate to aqueous alteration in CM chondrites [7]. Shifts in this feature indicate BM.2022,M2-41 is more aqueously altered than BM.2022,M1-91. This is consistent with the determined mineralogy [1]. Bidirectional Reflectance Distribution Function (BRDF): The BRDF was measured for a powdered sample of the Winchcombe meteorite (BM.2022,M1-22) across 0 - 70° reflectance angles, in steps of 5°; at 15°, 30°, 45° and 60° incidence angles; and at 0°, 90° and 180° azimuthal angles. The dataset was then fitted using the Hapke BRDF model to enable constraints to be placed on the bulk scattering properties of the meteorite sample [8]. Importantly, the surface profile of the sample was characterized using an Alicona 3D® instrument. Therefore, two of the free parameters within the model - the filling factor, φ; and the RMS slope angle, θ - could be set, as φ = 0.65 ± 0.02 and θ = 16.11° (at 500 μm size-scale). This enabled w, b and hS to be set as the three open parameters within the Hapke BRDF model Least-Squares Levenberg-Marquardt fitting function. The best fit Hapke parameters were determined to be w = 0.152 ± 0.030, b = 0.633 ± 0.064 and hS = 0.016 ± 0.008. From the BRDF dataset, the broadband albedo value was calculated to be A = 4.09 ± 0.18 %, which can be converted to hemispheric albedo by multiplying by π [8]. As with the reflectance samples (previous section), modal mineralogy and water abundance were obtained for BM.2022,M1-22 [2]. Summary: VNIR and MIR spectroscopy are highly effective tools used in planetary remote sensing to determine the composition and physical properties of rocks and minerals. Here we are able to catalog several important spectral features and derived properties of the Winchcombe material for comparison to other meteorites and asteroids. The laboratory measured Winchcombe BRDF provides a reference photometric dataset for use in remote sensing studies of similar airless bodies, and by combining the IR spectra of the pristine Winchcombe material with other measurements on Earth, we can better understand and interpret data from Solar System objects and, in turn, learn more about their origins and evolution. [ABSTRACT FROM AUTHOR]