In this work, we propose a new potential mechanism for the formation of the so-called hollows on Mercury, hypothesizing that they are composed of carbonatites - volcanic rocks that are exceedingly rare on Earth. To evaluate this hypothesis, mid-infrared spectroscopic measurements were performed on a rare, unaltered terrestrial carbonatite sample from Mount Ol Doinyo Lengai, Tanzania, composed primarily of the carbonate minerals nyerereite and gregoryite. For comparison, spectra of several common terrestrial carbonate minerals were also acquired. The collected spectra display characteristic features of carbonate minerals. Our analysis suggests that carbonatite rocks should be taken into account for several physical properties required for the formation of hollows on Mercury's surface. These include appropriate thermal stability, chemical composition, and surface coloration. In particular, the eruption temperatures of terrestrial carbonatite lavas are less than 100 degrees C below Mercury's estimated daytime surface temperatures. This thermal similarity makes the measured spectra relevant for the MERTIS instrument onboard the BepiColombo spacecraft, which will investigate Mercury's surface mineralogy in near future.

An unusual chondritic xenolith was found in two sequentially prepared thin sections of a sample from the Krymka (LL3.2) chondrite. The xenolith has a rounded, slightly deformed shape of about 5 mm in apparent diameter and is partially surrounded by a double rim made of an inner fine-grained silicate-rich rim and an outer sulfide-rich rim. The xenolithic inclusion is characterized by partially equilibrated mineral constituents, a recrystallized chondritic texture with relic chondrules, and a high abundance of CAIs (0.11 vol%). Within the core of the xenolith, olivine and low-Ca pyroxene are the most abundant mineral phases, and randomly analyzed grains by grid analysis revealed mean compositions of Fa9.8 +/- 5.5 and Fs7.2 +/- 4.4Wo2.9 +/- 2.2 for olivine and low-Ca pyroxene, respectively. Within the entire clast, a feldspar-normative mesostasis is embedding all constituents, indicating partial melting of the xenolith, probably during impact metamorphism. Thus, the xenolithic clast is very likely an impact melt rock. Infrared (IR) spectroscopic studies revealed the dominance of olivine and low-Ca pyroxene in the obtained spectra from the fine-grained silicate-rich rim of the xenolith. Oxygen isotope analyses by SIMS show that, in the three-oxygen isotope diagram, most individual olivine grains from the xenolith plot within the field of bulk ordinary chondrites and their chondrules, except for three olivines: Two grains from the xenolith's core (Delta 17O = -1.6 +/- 0.5 parts per thousand and -2.4 +/- 0.5 parts per thousand) and one olivine from the rim (Delta 17O = -6.5 +/- 0.4 parts per thousand) show significant 16O enrichments. The chondritic impact melt rock studied here clearly demonstrates that this xenolithic clast formed prior to the Krymka parent body accretion within another pre-existing chondritic parent body. While previous studies have discussed a potential late-stage accretion of large Krymka constituents, the components within the apparent first-generation parent body experienced thermal annealing, and, subsequently, the xenolith suffered partial melting due to a shock event that probably caused this fragment to be ejected from its first-generation parent body.

Space weathering (SW) on airless Solar System bodies is a critical process affecting the properties of surface materials. SW alters the spectral properties of surface minerals, which are investigated via remote sensing. Understanding the mechanisms of SW is therefore essential to correctly interpret measurement data and to reconstruct the evolution of these surfaces. One of the primary drivers of SW are micrometeorite impacts. To investigate the influence of micrometeorite impacts on various surface materials, numerous analog studies have been conducted over the past 30 years. A frequently used approach in these studies is the simulation of micrometeorite impacts using laser irradiation. Although it has been demonstrated that these analog experiments produce representative results, the actual time scales being simulated remain an open question. This matter is a fundamental issue, as SW is a time-dependent process. Therefore, this study presents a tool to calculate equivalent simulation times for such laboratory analog experiments. To this end, various parameters were gathered from the scientific literature and integrated into the calculation. These variables can be used in their current form or updated in the future when more precise data become available.

We present mid-infrared transmission spectra from 2 to 23 microns of the 23 Atacama Desert chondrites of different types (carbonaceous Ornans and ordinary of H, L, and LL groups) as well as of some pure minerals (olivine and diopside). We focus on the characteristics of silicate at 10 and 20 microns, analyzing the influence of composition and grain size on peak strengths and spectral shapes. We present the first results of the Cosmic Dust Laboratory, a dedicated facility at the Universidad Diego Portales equipped with a VERTEX 80v vacuum Fourier transform infrared spectrometer. Through milling and sieving samples, we obtained different ranges of particle sizes to study the effect of grain size on the intensity and shape of the spectrum. The resulting spectral library can be compared with astronomical data of protoplanetary disks, debris disks, and even white dwarf disks obtained with instruments such as MIRI on board the James Webb Space Telescope and MATISSE on the Very Large Telescope Interferometer. We also present mass absorption coefficient values, which can be used for radiative transfer modeling of astronomical observations. This study aims to improve dust opacities for astronomical applications, with a focus on circumstellar disks.

Understanding the unique spectral signatures of glasses is relevant in a remote sensing context. Three basaltic glasses characterized by the system SiO2-Al2O3-MgOCaO, with up to 0.3-3.7 wt. % FeO, 0 to 7.0 wt. % Na2O, and <1 wt. % of TiO2, Cr2O3, MnO, and K2O are investigated spectrally in this study. We found a flank-like attachment to the dominant mainband vibration (similar to 1060 and 944cm(-1)) located between 800 - 650cm(-1) in the reflectance mid-infrared spectra (MIR) that correlates well with the respective polymerization degree of the glass. We furthermore report the occurrence of a peak splitting in the mainband vibration in the sodium - poor glass batch between 1180 and 900cm(-1), which is not attributable to incipient crystallization processes, but is probably caused by Mg2+ assuming roles as both, charge balancing cation and modifier. The results of this study were compared with glasses from Chang'E lunar samples reported by Zeng et al. [1].

Aims. We present mid-infrared transmission spectra from 2 to 23 μm of the 23 Atacama Desert chondrites of different types (carbonaceous Ornans and ordinary of H, L, and LL groups) as well as of some pure minerals (olivine and diopside). We focus on the characteristics of silicate at 10 μm and 20 μm, analyzing the influence of composition and grain size on peak strengths and spectral shapes. We present the first results of the Cosmic Dust Laboratory, a dedicated facility at the Universidad Diego Portales equipped with a VERTEX 80v vacuum Fourier transform infrared spectrometer. Methods. Through milling and sieving samples, we obtained different ranges of particle sizes to study the effect of grain size on the intensity and shape of the spectrum. Results. The resulting spectral library can be compared with astronomical data of protoplanetary disks, debris disks, and even white dwarf disks obtained with instruments such as MIRI on board the James Webb Space Telescope and MATISSE on the Very Large Telescope Interferometer. We also present mass absorption coefficient values, which can be used for radiative transfer modeling of astronomical observations. This study aims to improve dust opacities for astronomical applications, with a focus on circumstellar disks.

The MErcury Radiometer and Thermal infrared Imaging Spectrometer (MERTIS) is part of the payload of the Mercury Planetary Orbiter spacecraft of the ESA-JAXA BepiColombo mission. MERTIS combines an imaging spectrometer covering the wavelength range of 7-14 μm with a radiometer covering the wavelength range of 7-40 μm. The instrument will map the whole surface of Mercury with a spatial resolution of 500 m for the spectrometer channel and 2 km for the radiometer channel. The compositional map of Mercury provided by MERTIS will allow unique insights into the evolution of the least explored terrestrial planet and will directly address questions raised by the NASA MESSENGER mission. For example, MERTIS will be able to provide spatially resolved compositional information on the hollows and pyroclastic deposits and answer the question whether hollows are actually predominately composed of sulfide. MERTIS will also provide spatially resolved temperature maps inside the permanently shadowed craters, thereby potentially constraining the stability of water ice deposits in those craters.BepiColombo is currently in the final part of its 7-year journey to Mercury. The interplanetary cruise includes in total nine flybys for gravitational assists: one at Earth, two at Venus and six at Mercury. MERTIS could obtain so far observations during the Earth flyby in April 2020, the first Venus flyby (FB1) in October 2020 and the second Venus flyby (FB2) on August 10, 2021. The recently published results for FB2 show that MERTIS performed well beyond requirements and provided new insights into the long-term stability of the Venusian atmosphere.

The Apollo 14 regolith breccia 14076 contains glass beads with extreme compositions that fall in two groups; (1) both high-alumina, silica-poor (HASP), interpreted as evaporation-residues, and (2) gas-associated spheroidal precipitates (GASP), impact vapor condensed to glassy spheroids [1,2]. Here, we present high-resolution quantitative EPMA data of the previously studied thin section 14076,5 and for the first-time data on thin section 14076,21. In addition, we present spectroscopic data of these unique glass samples, including in-situ mid-IR reflectance spectroscopy and Raman spectroscopy. The spectral characterization of the unique glasses in sample 14076 is in preparation for the ESA/JAXA mission BepiColombo to Mercury, which carries the Mercury Radiometer and Thermal Infrared Spectrometer (MERTIS) that will map the surface of the planet in the spectral range of 7 to 14 µm. Given the higher gravity and surface temperature on Mercury compared to the Moon, the regolith on Mercury likely contains exotic materials similar to HASP and GASP that formed in energetic impacts. Models suggest that these materials have more than an order of magnitude higher abundances on Mercury compared to the Moon [3], at levels detectable by the BepiColombo mission. A potential quantification of these materials in the Mercury regolith requires detailed spectral and chemical characterization of similar materials in the laboratory. Here, Apollo 14 sample 14076 provides a unique “analogue” material.Quantitative elemental maps for SiO2, TiO2, Al2O3, CaO, MgO, FeO, Na2O, K2O, CrO, and S were measured with a JEOL JXA 8530F electron microprobe operated at 15 keV accelerating voltage and a probe current of 80 nA. Spatial resolution varied with the highest resolution scan steps of 0.1 µm and mapped areas of up to 200 µm in diameter. Average compositions of homogeneous areas were manually extracted from the quantitative maps using Fiji (ImageJ). Fourier Transform Infrared (FTIR) spectra were measured with a Bruker Hyperion 3000 microscope attached to a Vertex 80v FTIR-spectrometer and equipped with a focal plane array (FPA) mapping detector and a 15x Cassegrain objective. Spectra were recorded over the spectral range from 2.5 to 16.7 µm wavelength. Raman spectra were recorded with a high-resolution Horiba HR800 spectrometer and an Olympus microscope, focusing the laser beam to a 1-2 µm spot on the sample. The GASP spherules and agglutinates fall in two compositional categories. Si-GASP [2] have SiO2 concentrations of 97±2 wt.% with ~1 wt.% FeO and 0.5 wt.% CaO. In contrast, Fe-GASP have lower SiO2 contents of 61±6 wt.%, and high FeO (27±7 wt.%) and MgO (up to 20 wt.%) concentrations. These two GASP components are the product of silicate melt immiscibility in the SiO2-FeO and SiO2-MgO systems [4]. The observation of Fe-metal nuggets in some of the FeO-rich glasses constrain to fO2 of the GASP beads at the iron-wüstite (IW) mineral buffer. The most abundant HASP particles are glassy and fall in a very narrow compositional field with 22±1 wt.% SiO2, 52.4±0.8 wt.% Al2O3, and 27.9±0.6 wt.% CaO. Quench crystals in some HASP particles can be identified as the lunar mineral yoshiokaite [5], for which we provide the first FTIR-spectrum. Figure 1 shows a data compilation of mid-infrared spectroscopy “Christiansen Features” in glasses as a function of the SiO2 concentration. The HASP and GASP glasses have extremely low-, and extremely high SiO2 contents respectively, and accordingly extreme spectral properties not previously characterized by FTIR or Raman.Finally, our observations of Fe metal nuggets in the FeO-bearing GASP glass provide a direct constraint on fO2 in the condensing impact vapor plume, at the IW buffer. This is the same oxygen fugacity as determined for lunar mare basalts at IW-2 to IW+0.2 [11], which are a potential impact target and source of the material in the plume. This suggests that evaporation and condensation inside the plume did not affect the fO2.Figure 1: Relationship between the FTIR Christiansen Feature and the SiO2 concentration in the respective glasses in wt.%. The data represent experimentally synthesized glasses with compositions representing compositions from Mercury, the Moon, Venus, Mars, and the Earth, laser impact experiments, and terrestrial impact glasses and tektites [6-10]. The HASP and GASP glasses fall in the shaded regions with very high- and very low SiO2 contents, significantly extending the compositional range for which mid-IR spectral properties are determined.References: [1] Vaniman D.T. (1990) LPSC 20:209–217. [2] Warren P. (2008) GCA 72:3562–3585. [3] Cintala M. J. (2012) J. Geophys. Res. 97:947–973. [4] Fabrichnaya B. B. (2000) Calphad 24:113–131. [5] Vaniman D. T. & Bish D. L. (1990) Am. Min. 75:676–686. [6] Morlok A. et al. (2016) Icarus 264:352–368. [7] Morlok A. et al. (2016) Icarus 278:162–179. [8] Morlok A. et al. (2017) Icarus 296:123–138. [9] Morlok A. et al. (2020) Icarus 335:113410. [10] Morlok A. et al. (2021) Icarus 361:114363. [11] Fogel R. A. & Rutherford M. J. (1995) GCA 59:201–215.

We synthesized the solid solution between the sulfides CaS (oldhamite) and MgS (niningerite). Electron microprobe and X-ray diffraction showed homogeneous and pure samples after the synthesis. The calculated lattice parameters fit to earlier literature data. Mid-infrared spectroscopy of the samples reveal that the produced sulfides were fragile and tend to alternate very fast. However, we were able to provide clean reflectance spectra of all samples. The spectra of un-altered samples show no peaks or bands but a rather constant spectrum within the analyzed spectral range between 7.0 and 12.5 mu m. The altered spectra contain signatures of sulfates and carbonates and probably further compounds. The gathered data help to understand the formation conditions of the studies sulfides as it shows that the solvus exists in the CaS-MgS system between 1000 degrees C and 1200 degrees C. In addition, the infrared data will help to improve remote sensing in the mid-infrared of planetary objects that might be covered with sulfide containing material like asteroids or Mercury. Oldhamite and niningerite are known to occur naturally in meteorites like aubrites. From that, some asteroids must partly consist of those minerals. In addition, Mercury is also known to consist of much sulfur and therefore suggested to have sulfides of the solid solution between oldhamite and niningerite on its surface. Investigating those minerals will therefore help to understand the formation conditions that lasted on those planetary objects. Hence, we were the first who produced the full solid solution of sulfide minerals between oldhamite (CaS) and niningerite (MgS). Those minerals can only form at very special conditions that we reconstruct in the laboratory because at normal conditions on Earth they are very unstable. We investigated the synthesized samples with X-ray diffraction, electron microprobe analyzer, and infrared spectroscopy in the wavelength range between 7.0 and 12.5 mu m, which is used for remote sensing. Our data confirmed earlier literature data in terms of lattice parameters and reveal that our experiments produced the sulfide samples correctly. Therefore, our data will help improve remote sensing of asteroids and potentially of planet Mercury. The gathered data are freely available at the IRIS infrared database. Oldhamite is rapidly altered at the surface when exposed to air even under deliberately careful sample handling and dry air storage Expected flat spectra show bands of beginning alteration in the form of sulfites, sulfates and carbonates Spectra of epoxy embedded samples show uniform spectra over the entire spectral range without bands

Glassy materials have been recognized over Mars, Moon and many different meteorites (Farrand et al. 2016; Delano 1986; Varela & Kurat 2004). Planetary glasses result from impact events but they are also found as volcanic products (Farrand et al 2016). Morlock et al. (2017) and Morlok et al. (2021) investigated by means of different experimental techniques (bi-directional diffuse reflectance FTIR, in situ FTIR microscopy, Raman, EPMA and optical microscopy) a suite of synthetic samples with composition similar to those inferred for different Hermean terrains. Here we extended the study of the same materials to the VNIR region (bidirectional reflectance spectroscopy: 350 to 2500 nm). We analyzed 8 different samples with different chemical compositions, produced under different oxygen fugacity conditions We prepared eight granulometric classes between 0 and 250 μm, namely: 0-25; 25-63; 63-100; 100-125; 125-150; 150-180; 180-200 and 200-250 μm. The dominant feature in the VNIR region is due to the Fe absorption band at about 1 μm accompanied, in the more oxidized samples, by a smaller feature at 480 nm likely due to ferric oxide development. Iron free samples (FeO < 0.1 wt%) show characteristic spectral shapes with a distinctive feature at about 640 nm attributable to TiO2. Even for very low FeO content, it is possible to observe a weak yet clear band at about 900-1000 nm due to Fe absorption which explain the dominance of the spectral features due to Fe absorption at higher FeO content. Additional small bands at higher wavelengths (1300-1400 and 1900 nm) suggest a low content of water and/or –OH species in the samples. We investigated the spectral features as a function of composition, grain size and oxidation in order to gain as much information as possible on the nature of the spectra and compare them with remote sensing data or meteorites VNIR comparison. Our data on synthetic and realistic Hermean compositions will allow a better understanding of remotely acquired VisNIR spectra, which will be particularly helpful in view of the upcoming beginning of the BepiColombo ESA/JAXA mission. Acknowledgments: The authors acknowledge financial contribution from the Italian Space Agency (ASI) under ASI-INAF agreement 2017-47-H.0 (Simbio-SYS). CC, EB are also supported by agreement ASI-INAF n.2018-16-HH.0.

We studied a series of hermean lava analogs in the mid-infrared (2.5 pm-18 pm) to provide characteristic spectra for enstatite basalt, the Northern Volcanic Plains and Na-rich Northern Volcanic Plains. Our aim is to provide spectra for the interpretation of the data expected from Mercury from the MERTIS (MErcury Radiometer and Thermal Infrared Spectrometer) instrument on the ESA/JAXA BepiColombo mission. Bulk powder spectra show bands of glass with a dominating broad Si-O-Si stretching feature around 10 pm. Crystalline components are mainly enstatite and forsterite with Reststrahlen Bands (RBs) around 9.3 pm, 9.6-9.9 pm, 10.0 pm, and 10.3-10.7 pm. Increasing intensity of crystalline features in the spectra reflect the increase in the crystallites in glass with decreasing temperature of equilibration and quenching. Micro-FTIR data allowed to extract spectral of individual components and glass. The position of the Christiansen Feature (CF) has only a weak correlation with the degree of crystallinity. Correlations are observed between the Christiansen Feature (CF) and the bulk SiO2 content of the materials, as does the correlation of this feature with the compositional index SCFM = SiO2/(SiO2 + CaO + FeO + MgO) on an atomic basis. This study also confirms the correlation line of glass-rich, irradiated Mercury analogs in these systems (Weber et al.,2023), indicating a similar spectral response of the glass rich materials expected for the surface of Mercury. The position of the strongest silicate main band (MB) compared to the SiO2 content, confirms a trend for samples formed in experiments simulating high velocity impacts fall on a different trend line than analog samples formed in magmatic processes. A comparison of the results to an Earth-based hermean surface spectrum showed similarities to spectra obtained for NVP samples.

Introduction: The IRIS (Infrared and Raman for Interplanetary Spectroscopy) laboratory at the Institut für Planetologie in Münster produces a database of mid-infrared spectra for the ESA/JAXA BepiColombo mission to Mercury. The MERTIS (Mercury Radiometer and Thermal Infrared Spectrometer) instrument onboard the BepiColombo Mercury Planetary Orbiter allows mapping spectral features in the 7-14 µm range, with a spatial resolution of about 500 meters [1,2].In addition to a variety of natural terrestrial and meteoritic materials for the comparison of the expected results, we started using synthetic analogues based on the chemical composition of Mercury measured by MESSENGER. This allows to produce infrared spectra of bodies from which no material as returned samples or meteorites is available so far [3-5]. Advanced modelling based on the chemistry of Mercurian lavas and high-temperature experiments to simulate the mantle formation and the crystallization of lavas at the surface resulted in prediction for modal mineral compositions for distinct surface regions [6-8]. This allows to produce synthetic mixtures of minerals and glass representative for these hermean regions. Samples & Techniques: For the first round of mixing studies of powdered samples, sample compositions were selected from modal compositions based on experiments covering the dominant mineralogically diverse, 3.6–3.5 Gyr old volcanic smooth plains regions on Mercury [6,7]. The experimental conditions (for details see [7,8]) were temperatures between 1170-1360°C and highly reducing conditions (ΔIW of -4.9 to -6.2). Of the run products described in [7], we picked modal compositions covering a wide range of phase compositions, ranging from pure glass to the most crystalline composition modelled (crystalline content from 9-58 wt%).The analogues were prepared using mixtures of synthetic glass material based on hermean compositions [7-9] and natural crystalline forsterite, enstatite, diopside and plagioclase, with compositions in the range that was observed in the petrological experiments [7]. All materials were sieved into 4 size fractions before (0-25 µm, 25-63 µm, 63-125 µm, 125-250 µm), and the analogue mixtures composed directly from the size fractions.Diffuse reflectance mid-infrared spectra were made with a Bruker Vertex 70 infrared system using a Cooled MCT detector. Analyses of the powders were made at low pressure (10-3bar) to reduce atmospheric bands from 2-20 µm. For calibration, a diffuse gold standard was used for ratioing, to guarantee low noise, we integrated 512 scans for each spectrum. Spectral features of interest are the Christiansen Feature (CF), a characteristic reflectance low that also serves as proxy for the bulk composition; the Transparency Feature (TF), typical and indicator for the finest grain size fraction (0-25 µm); and the Reststrahlen Bands (RBs), the molecular vibration modes. Results: In the range of interest for MERTIS (7-14 µm), the entirely glassy end member shows a simple spectrum with a strong RB at 9.6 µm, a CF at 7.9 µm and the TF at 11.77 µm [4]. Increased crystalline content (9 wt% forsterite, 91 wt% glass) in sample ID 345 Smooth Plains has two RB appearing at 9.6 µm and 10.5-10.6 µm, and a weaker RB at 10.2 µm. The CF is at 7.9-8 µm, the TF at ~11.7 µm.Sample ID 344 Smooth Plains contains several crystalline species (5 wt% forsterite, 2 wt% diopside, 28 wt% plagioclase and 11 wt% enstatite). This results in a feature-rich spectrum, with RBs at 9.5 µm, 9.9 µm, 10.2 µm, 10.5 µm, 10.8 µm, 11.1 µm and 11.3-114 µm. The CF is found at 7.8-7.9 µm, the TF is at 11.7 µm.The crystalline-rich end member ID 343 Smooth Plains has only 42 wt% glass components with 6 wt% forsterite, 11 wt% diopside, 34 wt% plagioclase and 7 wt% enstatite. RBs are seen at 9.4 – 9.6 µm, 9.9 µm, 10.2 µm, 10.5 µm, 10.8 µm and 11.3 µm. The TF is at 11.6 µm, the CF at 7.9 - 8 µm.Discussion: Spectra show increasing RB features with decreasing content of glass (Fig.1). However, a comparison of the finest size fractions (0-25 µm) (Fig.2) of the 4 samples shows astonishingly similar spectra, basically the smooth glass spectra of with relatively weak RB on top, with the spectrum dominated by the TF. This could make distinguishing of such spectra of a continuum of similar composition difficult.Contrasts between the spectra are stronger at the larger grain size fractions (>25µm), where the RB features are stronger. Variations in band intensities between the different samples – particular the high intensity of the ID 344 Smooth Plains spectrum – could be results of a highly reflective component (Enstatite?) or indicator of insufficient mixing of the phases.Summary & Conclusions: We will continue by mixing further samples based on the hermean surface models and experiments [7], with the aim to have series of samples representative for each of the terranes. Future spectral unmixing models will test if the individual mineral components can be extracted by modelling form the spectra.References: [1] Benkhoff J. et al. (2020) Planetary and Space Science 58, 2-20 [2] Hiesinger H. et al. (2020) Planetary and Space Science 58, 144–165 [3] Morlok et al. (2020) Icarus 335, 113410 [4] Morlok et al. (2019) Icarus 324, 86-103 [5] Weber et al. (2020) Earth and Planetary Science Letters 530, 115884 [6] Weider S.Z. et al. (2015) Earth and Planetary Science Letters 416, 109-120 [7] Namur and Charlier (2017) Nature Geoscience 10, 9-15 [8] Namur O. et al. (2016) Earth and Planetary Science Letters 448, 102-114 [9] Nittler L.R. et al. (2018) Mercury: The View after MESSENGER. Cambridge University Press, Cambridge, pp. 30-51.Figure 1. Mid-infrared diffuse reflectance spectra of 4 size fractions. CF: Christiansen Feature, TF: Transparency Feature.Figure 2. Mid-infrared diffuse reflectance spectra of the 0-25 µm size fractions.

The Mercury Radiometer and Thermal Infrared Spectrometer (MERTIS) is part of the ESA-JAXA BepiColombo science payload en-route to Mercury. On April 10th 2020, BepiColombo flyby the Earth and obtained data from the Moon surface at a distance of around 700,000 km. The MERTIS thermal-infrared spectrometer (TIS) operating between 7 mu m and 14 mu m recorded more than 9,600 single hyperspectral observations of the Moon through its space baffle built for deep-space calibration. MERTIS has been designed to observe the surface of Mercury at a spatial resolution more than 1000 times better and at temperatures up to 2 times greater than that of the Moon. Therefore, lunar observations present a significant challenge for the instrument and the team. The standard acquisition procedure and the operations software were adapted to obtain data during the BepiColombo cruise phase. A specific calibration procedure and spatial binning have been developed to obtain the best radiometric data from the lunar surface. The calibrated data demonstrate the exceptional performance of the instrument, developed for a very different planetary object, comparable with ground-based measurements. The observations made during the cruise phase are very promising for future observations of Mercury with the space baffle during the fifth Mercury flyby scheduled for December 2024 and the nominal nadir viewing port (planet baffle) in orbit around Mercury.

Introduction: The MERTIS (MErcury Radiometer and Thermal Infrared Spectrometer) onboard of the BepiColombo ESA/JAXA mission to Mercury is a mid-infrared instrument that will allow mapping the hermean surface from 7 µm to 14 µm [1,2]. After arrival in 2025, a database for the interpretation of the data is needed. As part of this effort, we have studied rock samples like impact rocks and meteorites [e.g,. 3]. A second field of interest are analogs synthesized based on data by MESSENGER [e.g., 4].Based on recent modeling of the oxidation state of the hermean surface, a highly reducing environment can be expected [5,6]. Likewise past volcanism or impact experiments suggest the presence of extremely reduced phases, e.g., Si-metal (e.g, 7, 8]). This implies that in addition to common minerals (pyroxene, plagioclase), also oxides (corundum, spinel, periclase), metallic phases, halides, and reduced variations e.g. of olivine (Ca-olivine Larnite) are possible. As part of our database project, we cover this type mineral phases.Samples and Techniques: We characterized the materials first with EMPA. Samples were ground and sieved into grain four size fractions (

Introduction: The purpose of the IRIS (Infrared and Raman for Interplanetary Spectroscopy) laboratory is to produce laboratory spectra for the mid-infrared spectrometer MERTIS (Mercury Radiometer and Thermal Infrared Spectrometer) on the ESA/JAXA BepiColombo mission to Mercury. This device will map the mineralogy of the hermean surface spectral features in the 7-14 µm range, with a spatial resolution of ~ 500 meters [1,2]. For the interpretation the data from MERTIS, we need laboratory spectra for comparison. A wide range of natural mineral and rock samples such as terrestrial impact rocks and meteorites [e.g., 3-5] was studied for this purpose. Since we do not have natural samples from surface of Mercury, we produced synthetic analogs based on MESSENGER data and laboratory experiments [6-9]. A central component for such mixtures will be glass to replicate material formed by impact events and lava extrusion and explosive volcanism (i.e., pyroclastic debris) [e.g. 10]. We present results of our ongoing study of synthetic glasses. These synthetic glasses will be studied in the mid-infrared to obtain spectra for the IRIS database, the material will also used for future mixtures and experiments.Samples and Techniques: Sample Production: In order to simulate the petrologic evolution of magmas on early Mercury, we synthesized analog material under controlled temperature, pressure and oxidation state [7-9]. The glass was produced following a procedure described in [11] with the oxidation state controlled by exposing the sample to a CO-CO2 gas-mixture equivalent to four orders of magnitude below the iron-wüstite buffer (IW-4). For in-situ studies we selected run products from earlier, similar laboratory experiments [9].Infrared Spectroscopy: For the bulk powder FTIR diffuse reflectance analyses, powder size fractions 0-25 µm, 25-63 µm, 63-125 µm, and 125-250 µm were measured, in addition to a polished sample. We used a Bruker Vertex 70 v infrared system with a MCT detector at the IRIS laboratories at the Institut für Planetologie in Münster. Analyses were conducted under low pressure to reduce atmospheric bands, analyses were made in reflectance from 2-20 µm.FTIR microscope analyses for in-situ studies in polished blocks and thin sections were conducted using a Bruker Hyperion 1000/2000 System at the Hochschule Emden/Leer. We used a 250×250 µm sized aperture. In addition, a Perkin-Elmer Spotlight-400 FTIR spectrometer at the University of Manchester was used to map samples using an adjoining Focal Plane Array (FPA) mapping unit with a resolution of 6.25 µm × 6.25 µm.Results: Figure 1 gives an example of an area mapped using micro-FTIR. Sample 131_1 is based on the MESSENGER derived composition of the Mercurian High Magnesium Regions (HMg) [9]. Spectra in Fig.2 are of the Mg-poor (5.2 wt%) glassy component in this sample. Compared with spectra of glasses based on the Inter Crater Planes (ICP) (21.5 wt% MgO), 123_3 (17.7 wt% MgO) and 126_3 (12.2 wt% MgO), we see generally spectra typical for glassy materials. The single Reststrahlenband (RB) shifts with increasing MgO from 9.3 µm to 9.9 µm, and the CF from 7.9 µm to 8.2 µm.The two examples for bulk powders (Fig.3) have low MgO contents: 1.6 wt% (Low Mg C) and 4.7 wt % (Low Mg B) [9]. Different grain size fractions show intensity correlated with increasing grain size (Fig. 3). The RB and CF features are basically similar for all size fractions, but an characteristical Transparency Feature (TF) appears in the finest fraction (0-25 µm). The Low Mg B sample has the TF at 11.7 µm, the CF at 7.8 µm and the RB at 9.4 µm. Low-Mg C shows the CF from 7.6 µm to 7.7 µm, the RB at 9.2 µm – 9.3 µm and a TF at 11.6 µm.Summary & Conclusions: The sieved size fractions of the bulk glass material show typical features for highly crystalline materials. They follow a trend of band shifts for CF and RB towards longer wavelengths with increasing MgO contents [3,4]. We will present further glasses cover higher MgO contents (>6 wt%) to provide material for the whole range of expected Mercurian regolith glass compositions [7-9].However, for a complete picture of the hermean surface, we expect mixtures of glassy and crystalline material. This will be the next step in our study, where we will obtain spectra of mixtures representing various regions on Mercury [e.g.7,8]. Furthermore, the impact of space weathering, which changes the structural and thus spectroscopic properties of grain surfaces will be taken into account [12,13,14].References: [1] Rothery D.A. et al. (2020) Space Space Rev. 216, 66 [2] Hiesinger H. et al. (2020) in prep. [3] Morlok et al. (2020) Icarus 335, 113410 [4] Morlok et al. (2019) Icarus 324, 86-103 [5] Weber et al. (2020) Earth and Planetary Science Letters 530, 115884 [6] Weider S.Z. et al. (2015) Earth and Planetary Science Letters 416, 109-120 [7] Namur and Charlier (2017) Nature Geoscience 10, 9-15 [8] Namur O. et al. (2016) Earth and Planetary Science Letters 448, 102-114 [9] Namur O. et al. (2016) Earth and Planetary Science Letters 439, 117-128 [10] Fasset C.I. (2016) Journal of Geophysical Research: Planets 121, 1900-1926 [11] Renggli C. and King P. (2018) Rev.Min.Geochem 84, 229-255 [12] Weber I. et al. (2020) Earth & Planetary Science Letters 530, 115884 [13] Stojic et al. (2020) Icarus (submitted) [14] Stojic et al. (2020) LPSC 51, 1875

Introduction: Spectroscopic observations of asteroid Bennu suggest that the materials on the surface of the asteroid are most similar to aqueously-altered CM-or possibly CI-type carbonaceous chondrites [1]

Abstract The MErcury Radiometer and Thermal Infrared Spectrometer instrument onboard the BepiColombo spacecraft is designed to investigate Mercury’s surface in the mid‐infrared (mid‐IR). Based on MESSENGER data and modeling, Mercury is thought to be evolved under highly reducing conditions (e.g., McCubbin et al., 2017, https://doi.org/10.1002/2017JE005367; Namur & Charlier, 2017, https://doi.org/10.1038/ngeo2860). The modeling also indicates that Mercury's surface is rich in feldspar. However, it is unknown if reducing conditions during the emplacement of volcanic melts have an influence on the IR properties of feldspars. Therefore, we investigated basaltic samples from the Bühl quarry in northern Hesse, Germany, that evolved under reducing conditions in the mid‐IR and compared the spectra with samples that experienced more oxidizing conditions during their formation. The Bühl samples are feldspar‐rich and contain metallic iron in some areas. Our investigations show that there are no differences between feldspars that formed under different oxidizing conditions. All spectral properties could be explained by well‐known factors that affect mid‐IR spectra of silicates.

The effect of surface regolith gardening and melt layer production produced by space weathering (SW) (owing to micrometeorite bombardment) of surficial regolith layers of airless planetary surfaces was investigated in an experimental setup by using laser-induced ablation of powdered analog material (synthetic Fo100) under vacuum with a ns-pulsed infrared laser. The investigated analog pellets were prepared from the fine fraction (< 1 mu m) up to a grain size of 280 mu m, which resembles the uppermost regolith surface of many airless planetary bodies. The Fo-powder was pressed into shape to form a pellet. We focused here on nanometer-sized structural modifications that are induced in the relocated grains, sputtered off ejecta material and melt sprinkles that formed away from the craters caused by laser irradiation of the pressed pellet surface. The ejecta particles were redistributed over the entire pellet surface and beyond. The forming sputter film, melt sprinkles and ballistically ejected grains were caught on carbon film grids positioned nearby the craters. The grids were investigated with a transmission electron microscope (TEM) to discern between the distinct deposition types that were formed by ejecta condensate and partially molten ejected nanometer-size analog grains. Apart from a heavily modified pellet surface, we found that deposited droplets are mostly amorphous with minor nanocrystalline subdomains. Eight out of ten droplets show distinct incipient crystallization stages. This indicates at a relatively high amount of amorphous regolith material at the incipient stage of SW for airless bodies, if the regolith is altered via micro -meteorite bombardment.

The MERTIS (MErcury Radiometer and Thermal Infrared Spectrometer) onboard of the BepiColombo ESA/JAXA mission to Mercury will map the surface of Mercury in the wavelength range of 7-14 & mu;m and for the interpretation of these spectra a database of analog materials is needed. We analyzed bulk grain size fractions of a series of analog materials relevant to the distinct terranes of Mercury in diffuse reflectance in the mid-infrared (2.5 & mu;m to 18 & mu;m). Mineral mixtures cover a wide range of modal amounts of forsterite, enstatite, diopside and plagioclase, the resulting spectra can be divided into three distinct groups: (1) is dominated by a single glass feature, (2) by forsterite bands, and (3) by pyroxene bands. Despite often high contents, plagioclase features, are usually 'overprinted' by forsterite and pyroxene bands.Spectral parameter CF, an easy obtainable proxy for chemistry (SiO2) and polymerization (SCFM) places the hermean mixtures mostly in the intermediate and basaltic range. The correlation of parameters easily obtainable in remote sensing, Mg/Si ratio, and CF, allows differing materials from high-energy evaporation processes in impacts from such formed in igneous processes.Preliminary comparison with a spectrum covering most of the hermean surface shows some similarity with band positions of the Inter Crater Plain and Heavily Cratered Terrains (IcP-HCT) and High-Mg Northern Volcanic Plains (High-Mg NVP) mixtures, but none of our spectra is able to reproduce the remote sensing data entirely.