Introduction:  Dark surfaces, such as those found on planets asteroids and other primitive bodies, are the focus of past, present, and future space missions within the Solar System. Understanding the spectroscopic characteristics of these low albedo surfaces remains a significant challenge, with our current knowledge being incomplete. The presence of opaque materials [1] or surface processes like space weathering [2] or thermal alteration [3] often is linked with these dark surfaces. Interpreting remote sensing data necessitates intensive laboratory work, which serves as a pivotal tool in revealing the physical state and composition of these surfaces.

Analyzing complex mixtures of analogous materials remains one of the pivotal laboratory investigations to support remote sensing interpretation, but it also represents one of the most challenging experiments, in particular when multiple components are used in the mixtures. We present in this contribution several results from different works that share the common goal of studying how the mixing of different grain size and dark materials can affect the behavior of infrared spectra in the near- to mid-infrared range (1.25-25 μm).

Methods:  In this presentation, two primary studies will be outlined: the initial investigation delves into the combination of hydrated and anhydrous mineral components with varying grain sizes [4], while the subsequent study examines the blending of basalts with dark components at different grain sizes [5]. Samples prepared for both studies utilize an innovative protocol for mixing two components with distinct grain sizes. This method involves a sequence of steps, including sieving and mineral washing to isolate each grain size, followed by the mixing of the selected components. This procedure allows us to produce unique samples with a bigger grain size covered by a selected amount of small grains (Figure 1).

In the first work, we prepared several mixtures using 1 wt% and 5 wt% of hyperfine grain size (< 10 μm) of hydrated minerals and 95 wt% and 99 wt% of larger grain size (200–500 μm) of anhydrous minerals. We measured the IR reflectance spectrum of these mixtures in the range 8000–400 cm⁻¹ (1.25–25 μm). Analysis of the spectroscopic features was carried out independently in two separated ranges covered by our measurements, in the NIR range we focused on the presence of the hydrated band at 2.7 μm while in the MIR range we carried out an analysis of the most important spectroscopic features present. The second sample set includes four series of basaltic mix (feldspar and pyroxene), at different grain sizes from < 50 μm to 500-1000 μm, mixed with amorphous carbon at increasing weight percentages from 1% to 50%. We analyzed several features on the spectrum of each mineral mixture: (i) near infrared slope; (ii) 2.7 μm OH-stretching band; (iii) Christiansen features; (iv) Reststrahlen band and Transparency feature.

Figure 1. Secondary electrons SEM image of enstatite sample before (panel A and B) and after mixing with 5% and 1% of serpentine (panel C and D).

Results: The results of the first work [4] show how the addition of a hydrated component, which is minor in percentage and has a much smaller grain size, can lead to very remarkable changes in the NIR region especially in increasing the hydrated band depth at 2.7 μm (Figure 2), while slightly affecting the MIR region. The surface of many rocky bodies is covered with regolith, and these new laboratory data show how even a small amount of hydrated mineral in the composition can influence the final spectrum. Measurements presented in the second work [5] point towards a critical effect of dark material but with a different outcome for each grain size of the brighter component of the mixture (Figure 3). For the first time we investigate the spectral range from NIR to MIR. Some of the most interesting results involved the slope trend of modification with dark material, in particular we observed an inversion between reddening and bluing depending on the percentage of the mixture and the grain size. Moreover, we investigated also the different behavior of several features such as: hydrated band at 2.7 μm, the Reststrahlen band and Transparency feature.

Conclusion: Enhancing our comprehension of spectroscopic alterations resulting from minor fluctuations in mineral phases is crucial for accurately interpreting remote sensing data gathered from planetary surfaces by space missions. The dataset compiled from our experiments will serve as vital groundwork for interpreting forthcoming data from the JAXA Martian Moon eXploration mission. Additionally, it will aid in comprehending past data from dark surfaces within the Solar System, such as asteroids (162173) Ryugu and (101955) Bennu. Significant laboratory efforts are still required to effectively complement the analysis of remote sensing data, with numerous additional mixtures and combinations slated for investigation as a follow-up to this research. Further laboratory measurements will serve a dual purpose: expanding the database for interpreting planetary surfaces and furnishing reference spectra to enhance and validate current and future models.

Figure 2. Detail of hydrated band around 2.7 μm for hydrated minerals serpentine (top panels) and montmorillonite (bottom panels) with grain size <10 μm mixed at 1 wt% (dotted blue line) and 5 wt% concentration (dash-dot red line) with: plagioclase bytownite (panels C, G) and iron sulfide pyrite (panels D, H). (Figure adapted from [4])

Figure 3. Infrared spectra of basaltic mixtures [BAS] at different grain sizes, <50, 50-200, 200-500 and 500-1000 μm, with addition in different proportions, from 1 to 50%, with synthetic amorphous carbon [SAC] (Figure from [5]).

Acknowledgments: Authors thank Nathalie Ruscassier for the help with the SEM images acquisition and analysis. G.P., M.A.B., A.D. and A.W. acknowledge support by Centre National d’Etudes Spatiales (CNES). L.F. and J.R.B. acknowledge support from Italian Space Agency ASI-INAF agreement 2022-1-HH.0.

References: [1] Cloutis E. et al. (1990) Icarus, 84 (2), 315-333 [2] Hasegawa et al. (2022), ApJ. Let-ters, 939, L9 [3] Lugassi, R, et al. (2015), Geoder-ma, 213, 268-279 [4] Poggiali G. et al. 2023a, Icarus, 394, 115449 [5] Poggiali G. et al. 2024, A&A 685, A14

How to cite: Poggiali, G., Wargnier, A., Fossi, L., Iannini Lelarge, S., Beccarelli, J., Brucato, J. R., Barucci, M. A., Pajola, M., Masotta, M., Matsuoka, M., Beck, P., Nakamura, T., Merlin, F., Fornasier, S., Gautier, T., and David, G.: Linking laboratory and remote sensing investigations: grain size and mineral mixing studies as pivotal tools to interpret solar system exploration., Europlanet Science Congress 2024, Berlin, Germany, 8–13 Sep 2024, EPSC2024-913, https://doi.org/10.5194/epsc2024-913, 2024.

Introduction:

The JAXA Martian Moon eXploration mission will be launched in 2026 toward the Martian moon Phobos. The MMX infrared spectrometer (MIRS, [1]) will observe Phobos within the 0.9 to 3.6 µm range to detect potential signatures of organics and hydrated minerals. The existence of such signatures may shed light on the unknown origin of Phobos. In close collaboration with CNES and other French and Japanese laboratories, the LESIA – Paris Observatory is responsible for the development of the MIRS instrument. Along with the instrument development, in support of future MIRS observations, we already performed laboratory experiments to search for a Phobos spectroscopic simulant [2,3,4] and study the effects of observation geometry [3,4,5]. It is well known that surface porosity is an extremely important parameter of small bodies' surfaces, influencing their physical, spectroscopic, and photometric properties. However, the effects of porosity remain ambiguously understood with studies giving conflicting results (e.g., [6,7,8]). A high porosity is suggested for Phobos, in particular, because of the very low thermal inertia associated with the presence of a possible 10 µm plateau in the MIR spectra of Phobos [9,10]. Moreover, as an airless body, Phobos also undergoes significant space weathering from solar wind, galactic cosmic rays, micrometeorites, and sputtering of heavy ions from the Martian atmosphere [11,12] due to its proximity to Mars, with the solar wind being likely the most influential process for Phobos surface (Fig. 1).

In this work, we investigate the spectroscopic and photometric modification of Phobos regolith simulants induced by these two parameters: (1) porosity and (2) solar wind space-weathering.

Figure 1: Flux density at Phobos' surface of oxygen ions produced in the upper layer of the Martian atmosphere, and of hydrogen and oxygen ions from the solar wind.

Method:

To accurately represent the surface of Phobos, several samples were selected, including two Phobos simulants [4,5], olivine, phyllosilicate (saponite), coals (anthracite, DECS-19 from the Penn State Coal Bank), and iron sulfide (troilite). In particular, hydrated minerals and organics are important for Phobos, as the detection of these components could provide pivotal clues to decipher the origins of Phobos.

Figure 2: Evolution of a Phobos simulant during the sublimation experiment. The blue spectrum represents the initial spectrum and the red spectrum shows the final spectrum when the water ice is fully sublimated. One spectrum is taken every hour.

For the porosity effect study, porous Phobos simulants were created by sublimation of water ice mixed with grains (Fig. 2) of the Phobos simulants [14], resulting in a highly porous sublimation residue, as visible in Fig. 3. This study investigated the spectro-photometric variations induced by porosity using the SHADOWS spectro-goniometer [15] at IPAG (France) with spectroscopic measurements ranging from 0.4 to 3.6 µm. Additionally, mid-infrared (MIR) reflectance spectra (1.25 – 18 µm) were also obtained using the FTIR Bruker Vertex70v spectrometer. Our analysis in the MIR focuses on the modifications in shape and positional shifts of three key features for mineralogical interpretation: the Christiansen feature, the Restrahlen band, and the transparency feature.

For the space-weathering effect, we will present preliminary results on the irradiation of samples with 140 keV He and Ar ions with the ARIBE beamline at GANIL (France) to reproduce the effects of solar wind that reach and alter the Phobos’ surface. The use of two ions allows to explore different regimes of deposited dose.

Figure 3: SEM image of a porous sublimation residue of the UTPS-TB Phobos simulant.

Results:

Our results on porosity indicate that the spectrum samples tend to exhibit a bluing of its spectral slope in the visible and near-infrared after increasing porosity (Fig. 4). This spectral slope difference between a compact and porous sample may explain the difference between the blue and red unit on Phobos. In the mid-infrared range, the Christiansen feature is modified and the emissivity peak is larger for porous samples, leading to the formation of a 10 µm-plateau in the spectra of porous samples (Fig. 4). The study of the photometric properties reveals that porous samples exhibit a reduced single-scattering albedo and a slightly broader lobe that predominantly back-scattered, as for the compact samples, but with a higher contribution of forward scattering. The derivation of the Hapke parameters shows an increase in roughness for the porous sample, as expected by the macro-roughness visible on optical microscope images; but no modification of the opposition effect in contrast to what might have been expected with the modification of the surface texture. Additionally, phase reddening varies between compact and porous samples, suggesting it as an additional valuable observable for MIRS.

Figure 4: VNIR and MIR spectra of UTPS and OPPS before and after the sublimation experiment.

Conclusion:

This study gives novel and unique insights into the spectroscopic effects of porosity and solar wind on the regolith layer of Phobos, in the context of the upcoming JAXA/MMX mission, with interesting applications to the surfaces of other airless bodies. We will present, for the first time, the impacts of ion irradiation on the photometric properties of Phobos’ regolith, improving our understanding of space weathering processes.

Acknowledgments: The authors acknowledge the Centre National d’Etudes Spatiales (CNES) for the continuous support.

References: [1] Barucci et al. (2021), EPS, 73, 211 [2] Wargnier et al (2023a), A&A, 669 [3] Wargnier et al. (2023b), MNRAS, 524, 3 [4] Wargnier et al., submitted to Icarus (10.48550/arXiv.2405.02999) [5] Miyamoto et al. (2021), EPS, 73, 214 [6] Näränen et al. (2004), A&A, 426 [7] Hapke (2021), Icarus, 354 [8] Shepard and Helfenstein (2007), JGR, 112 [9] Giuranna et al. (2011), PSS, 59, 13 [10] Glotch et al. (2018), JGR, 123, 10 [11] Nénon et al. (2019), JGR, 124, 12 [12] Nénon et al. (2021), Nature Geoscience, 14, 2 [13] Quirico et al. (2023), Icarus, 394 [14] Poch et al. (2016), Icarus, 267 [15] Potin et al. (2018), AO, 57, 28

How to cite: Wargnier, A., Gautier, T., Poggiali, G., Poch, O., Moingeon, A., Quirico, E., Beck, P., Caminiti, E., and Doressoundiram, A.: Effects of porosity and space-weathering on the spectroscopic and photometric properties of Phobos simulants, Europlanet Science Congress 2024, Berlin, Germany, 8–13 Sep 2024, EPSC2024-917, https://doi.org/10.5194/epsc2024-917, 2024.

Introduction

Carbonate minerals are ubiquitous on Earth, on all terrestrial planets and on many satellites and small bodies, in particular asteroids. These minerals are identified through remote sensing using either visible and near infrared reflectance spectroscopy but also since recently Raman spectroscopy. These techniques, as well as mid-infrared spectroscopy, are also very frequently used in the laboratory to identify the various anhydrous, hydroxylated and hydrated carbonates phases.

In this talk we first report on an extensive ongoing experimental study of all types of carbonates by Visible, near and mir infrared and Raman spectroscopy of series of natural and synthetic samples, coupled with DRX and EPMA analysis to determine their mineralogical purity and their effective composition. We will focus here on the anhydrous calcite and dolomite groups including most of the rhombohedral carbonates.

In the second part we report on the detailed analysis of their spectra in order to finely determine the band positions, width and intensity of the bands as a function of composition (Ca, Mg. Fe, …). We also provide a vibration mode attribution to all the bands. Coupled with an exhaustive compilation and a critical review of the literature on the spectroscopic properties of these carbonates, this allows us to build accurate band list data to be ingested in the new band list database of the SSHADE database infrastructure (www.sshade.eu). These absorption and Raman spectral information for individual minerals as well as for solid solutions (e.g. the magnesite-siderite solid solution) are invaluable for the community, and are a type of information still critically missing to easily interpret laboratory, field or astronomical spectra.

Carbonate samples

A large set of samples (over 100) covering the anhydrous calcite and dolomite groups and including most of the rhombohedral carbonates (calcite, dolomite, ankerite, magnesite, siderite, rhodochrosite, smithsonite, sphaerocobaltite, kutnohorite, otavite and gaspeite) has been collected for this study. Most of the samples are of natural origin with a variety of composition, but a few pure minerals have been synthesized at ISTerre laboratory to complete the set, especially some hard-to-find natural end-members. They come from various sources, from the OSUG collection, from dealers and local collectors as well as from personal field collection in the mountain ranges around Grenoble. For the reflectance spectra part of the mineral have been grinded and sieved to either <25 µm, <50 µm or 50-100 µm size fractions. Selected grains (~1 mm) of each minerals have been also embedded in *** pellets and polished for EPMA and Raman measurements.

Spectroscopic experiments

Four series of spectroscopic experiments have been performed on various spectrometers.

• Raman emission microspectroscopy at a spatial scale of 1 micron were recorded on raw minerals, but also on selected grains embedded in pellets. We used 2 different instruments located at ENS-Lyon or ISTerre-Grenoble laboratories. Most spectra have been recorded with 1 cm^-1 resolution over the 50-1800 cm^-1
• Visible and near-infrared reflectance spectroscopy of raw mineral surfaces and mineral powders (mostly <25 µm and 25-100 µm fractions) in the range 400-4650 using our SHINE spectro-gonio radiometer. Measurements have been performed in standard geometry (nadir incidence, 30° observation) with a spectral sampling of 4 to 8 nm above.
• Mid-infrared reflectance spectroscopy of mineral powders (mostly the <25 µm fraction) in the range 500-7000 cm^-1 using our FTIR Brucker 70 spectrometer equipped with a bidirectional attachment. Measurements have been performed in standard geometry at 1 cm^-1 spectral resolution. The spot size is about 4 mm.

Figure 1: Raman spectra of a selection of anhydrous carbonates

Spectroscopic analysis

The analysis of the data mostly consisted in the measurement of the position (using peak fitting), width and intensity of all the observed emission or absorption bands. These parameters are then plotted one again each other to find the pairs which discriminate most efficiently between the different minerals. These band parameters are also plotted with the concentration of the different elements (Mg, Fe, Ca…) in order to determine which one may be a good proxy to determine accurately the composition of intermediate constituents in solid solutions.

Figure 2: Example of correlation between the positions of two Raman bands (υ_Tand υ_L) of different Ca-Mg-Fe-Mn-Zn carbonates.

Bandlist

An exhaustive compilation and a critical review of all the literature describing the infrared absorption and Raman emission spectroscopic properties of these carbonates has been performed. It has been complemented by our measurements to determine the range of values spanned by the position, width and intensity of all bands of all these carbonates.  These IR absorption and Raman emission datasets have then been complemented with metadata on the mineral composition and are now partly ingested in the band list database of the SSHADE infrastructure. The corresponding spectra are also available in the spectral databases of SSHADE. A carbonate band list or one of its IR or Raman band can be searched using the tools and the various filters provided by the SSHADE search interface.

Figure 3: The absorption band list of Calcite

Conclusion

This band list database fed with critical literature review complemented by laboratory measurements should become a key tool for astronomers and planetary scientists to identify unknown absorption bands observed in the spectra of the surface or atmosphere of many astrophysical and solar system objects. Once the best candidate solid found by the user, the tool will link to the most relevant spectral datasets present in the SSHADE databases. These data can then be used for direct comparison with observations, or to model them through radiative transfer codes.

Acknowledgements

We would like to thanks several local collectors who donated samples for this study, and the curator of the OSUG collection. The Europlanet 2024 Research Infrastructure project received funding from the European Union's Horizon 2020 research and innovation programme under grant agreement No 871149. We also acknowledge OSUG, and INSU for additional financial supports.

How to cite: Schmitt, B., Beck, P., Mandon, L., Leclef, A., Teixeira, F., Lanson, M., and Montes-Hernandez, G.: Reflectance and Raman spectroscopy of anhydrous carbonates for their identification at the surface of planetary bodies., Europlanet Science Congress 2024, Berlin, Germany, 8–13 Sep 2024, EPSC2024-1124, https://doi.org/10.5194/epsc2024-1124, 2024.

Here we present a summary and outlook of studies looking into and trying to understand the geomorphology and spectral appearance of devolatilization morphologies on the asteroid Vesta. These studies include remote observations and analysis of multispectral reflectance data obtained by NASA’s Dawn mission [1,2], heating experiments and reflectance measurements [3] executed at the Planetary Spectroscopy Laboratory [4] as well as observations and measurements via Electron Probe Micro Analysis [3].

The abovementioned devolatilization morphologies are the so-called pitted impact deposits (PIDs), which present themselves as densely clustered, polygonally-shaped pits [5] (Fig. 1a) within ejecta deposits. These PIDs show distinct spectral properties, whereas the exact cause(s) are still uncertain. The pyroxene-dominated reflectance spectra of the surfaces of these PIDs are characterized by higher overall reflectances in the visible and near-infrared light, more pronounced mafic absorption bands (Fig. 1b & 2a) and lower OH abundances (Fig. 1c) with respect to the adjacent material of the same ejecta deposit. PIDs mostly occur widely around one large, relatively young crater on Vesta [5, 1]. Some exhibit very large spectral differences with respect to their surroundings, and some do not. Those that exhibit the most distinct spectral characteristics and large differences with respect to their surroundings tend to occur in topographic traps like pre-existing impact craters [1]. During the abovementioned studies, several possible causes for these spectral differences could be excluded, like for example differences in grain size or differences in age/exposure to space weathering [1]. 

Fig. 1: a) Dawn FC clear filter image of a PID southwest of the parent crater Marcia. Resolution is around 20 m/px. b) RGB color composite highlighting the distinct spectral properties (higher reflectance and pyroxene absorption band depth). Resolution is around 60 m/px. R = 0.965/0.917 [µm], G = 0.750 µm and B = 0.750/0.917 [µm]. c) Dawn VIR 2.8 µm band depth data from [11], with greenish colors indicating less OH. Images taken from [1].

During our experiments [3], we heated Vestan analog materials and found that their spectral properties also changed upon heating (in vacuum), yet only beneath the surface. The sample surface itself turned darker than before heating, while the subsurface turned reddish to the naked eye. Reflectance measurements showed that the visible slope increased, as well as overall reflectance and even the pyroxene absorption band depth (with respect to the heated surface, Fig. 2b). EPMA furthermore revealed that hematite was formed within our sample, which indicates that an oxidation process occurred. Hematite formed as thin, amorphous-looking rims around diverse grains like FeS, pyroxenes or pure Fe metal (Fig. 3). The formation of hematite could explain the formation of higher reflectances and visible slopes, yet not the formation of the stronger pyroxene band depth.

Fig. 2: a) Dawn FC reflectance spectra of the pitted terrain (red) and its surrounding (yellow) shown in Figure 1 as indicated by the crosses. In addition, the reflectance spectrum of the average Vesta is shown. b) Laboratory-obtained reflectance spectra of the surface and interior of heated sample (Howardite NWA 5748 mixed with carbonaceous chondrite Murchison) to 600 °C for 72 h, showing the higher reflectance, visible slope and stronger mafic absorption of the interior. Figures taken from [3].

A current hypothesis suggests changes in the occupation of the M1 and M2 sites within the pyroxene crystals or the migration of iron cations within the crystal as the cause of the stronger mafic absorptions. This process might be triggered by the presence of volatiles. These volatiles may be prevented from quickly escaping into space when trapped deep enough in the deposit, gaining time to interact somehow with the surrounding material.

Fig. 3: Backscatter images of sample NWA5748M (Howardite NWA 5748 mixed with carbonaceous chondrite Murchison) heated to 600 °C for 72 h, obtained at the Museum für Naturkunde Berlin. A) Hematite rims around a composite grain of pyroxene and a sulfur-rich phase (that could not be identified). B) Hematite rims around FeS and Fe metal. Fe metal within the larger grain did not develop a hematite rim. C) Hematite rim around a Fe metal grain.

This was similarly hypothesized for oxidation experiments in air of terrestrial pyroxenes [6], which showed a similar behavior. In the case of Vesta and our experiments, the volatile species is most likely free OH released from phyllosilicates during the devolatilization of ejecta after deposition or of our analog material during heating, respectively. It is also plausible that the impactor that formed the large crater added volatiles into the ejecta, facilitating the prominent pit-forming devolatilization of ejecta. There is definite proof of the existence of relatively large abundances of OH on Vesta’s surface [e.g., 7], likely incorporated due to influx of carbonaceous chondrite material throughout geological time [e.g., 8,9].

TM has received federal funding (DFG project 528399203) to explore the causes that could influence the pyroxene’s reflectance spectrum during a devolatilization event. We will use Mössbauer spectroscopy in order to resolve the oxidation states of Fe in our heated and unheated analog samples. Moreover, we aim to use a specific EPMA method (flank method) developed by Dr. H. Höfer [10] in order to resolve the distribution of Fe cations within single pyroxene grains.

All this may lead to a better understanding of the interactions between volatiles (from exogenic input) and mafic material from differentiated planetary surfaces.

References

[1] Michalik et al. (2021) Icarus 369, Article 114633, doi: 10.1016/j.icarus.2021.114633

[2] Michalik et al. (2022) The Planetary Science Journal, 3:182 (15pp), doi: 10.3847/PSJ/ac7be0

[3] Michalik et al. (2024) Meteoritics & Planetary Science 1-34, doi: 10.1111/maps.14156

[4] Maturilli et al. (2019) SPIE Proceedings Vol. 11128, Infrared Remote Sensing and Instrumentation XXVII, 111280T, doi: 10.1117/12.2529266

[5] Denevi et al. (2012) Science 338, 246-249, doi: 10.1126/science.1225374

[6] Cutler et al. (2020) The Planetary Science Journal, Vol. 1, 1:21, doi: doi.org/10.3847/PSJ/ab8faf

[7] De Sanctis et al. (2012) The Astrophysical Journal Letters, 758:L36, doi: 10.1088/2041-8205/758/2/L36

[8] McCord et al. (2012) Nature Letter 491, 83-86, doi: 10.1038/nature11561

[9] Reddy et al. (2012) Icarus 221, 544-559, doi: 10.1016/j.icarus.2012.08.011

[10] Höfer & Brey (2007) American Mineralogist, Vol. 92, 873-885, doi: 10.2138/am.2007.2390

[11] Combe et al. (2015) Icarus 259, 21-38, doi: 10.1016/j.icarus.2015.07.034

How to cite: Michalik, T., Otto, K. A., Maturilli, A., Cloutis, E. A., and Hecht, L.: How and why can oxidation influence the reflectance spectrum of pyroxenes on planetary bodies?, Europlanet Science Congress 2024, Berlin, Germany, 8–13 Sep 2024, EPSC2024-1069, https://doi.org/10.5194/epsc2024-1069, 2024.

L-type asteroids are rare asteroids located throughout the Main Belt. They are unique among the minor bodies as their spectral appearance in the visible-near-infrared (VisNIR) is thought to be dominated by calcium–aluminium-rich inclusions (CAIs): agglomerates of minerals found in chondritic meteorites that contain the first solids that condensed in the solar nebula [1, 2].  A primary mineral phase in CAI is the aluminium oxide spinel (MgAl₂O₄), which presents an absorption feature at 2μm when enriched in iron due to thermal metamorphism. This absorption feature is observed in L-types, suggesting an enrichment of refractory inclusions in these bodies [3]. Therefore, the parent bodies of L-types might have formed at an early time and within a region of the protoplanetary nebula with a high concentration of CAI. If this is the case, the significance of L-type asteroids as tracers of planetary compositional and dynamical evolution cannot be overstated. The key question is: How rich in refractory inclusions are L-type asteroids?

Sunshine et al. (2008) concluded that some L-types contain between 22%-39% of FeO-rich CAI [4], an order of magnitude larger than what has been observed in the meteorite collection (<3vol%, [5]). Devogèle et al. (2018) confirmed the enrichment of most (but not all) L-types using the same methodology on a larger sample of L-type asteroids [6]. On the other hand, Mahlke et al. (2023) identified potential meteoritic analogues for several L-type asteroids among CO and CV chondrites [7], the meteorites with the highest CAI abundances, suggesting that L-types are at least partially sampled in the meteorite collection.

The discrepancy between the abundance models of asteroid spectra and direct comparisons with meteorite analogues may be in part due to the unknown spectral response of L-type material to secondary factors such as space weathering and phase-angle variations. While Lantz et al. (2017) have shown that CV and CO chondrites redden with increasing surface age [8], the response of the crucial 2μm band is unknown, though this information is paramount for deriving the CAI abundance in asteroids.

To quantify the effects of space weathering and phase-angle variations on spectra of L-type material, we collected nine samples of possible meteoritic analogues: 6 CV (2 of each subtype: reduced, oxidized-Allende-like, oxidized-Bali-like), 1 CO, 1 CK, and 1 CL chondrite.¹ Using the SHADOWS spectro-goniometer at IPAG, Grenoble [10], we acquired VisNIR spectra of the samples under multiple observation geometries to simulate the phase-angle variations of asteroidal targets as function of surface composition. For all samples, spectra are available from freshly-ground powders (in part newly acquired, in part from [11]) and from pressed pellets, further describing spectral changes due to surface texture and packing.

A particular focus of our experiment lies on the weathering-response of CAIs. To this end, we identified a large (>1mm in diameter) CAI rich in iron-bearing spinel in a section of CV Allende via scanning-electron microscopy, analogous to the inclusion expected on the asteroidal surfaces. For all samples (chondrites and CAI), we have concluded a dense spectral characterisation over a large wavelength range (VisNIR as described above and mid-infrared spectra at Synchrotron SOLEIL, Saint-Aubin), which is to be followed-up by ion irradiation using the INGMAR experiment (IAS & ICJLab, Orsay) to simulate space weathering by the solar wind [12]. We aim to acquire VisNIR spectra during the irradiation process at different dosages of ion implementation, capturing different degrees of space weathering. After irradiation, we aim to repeat the spectral characterisation executed before to capture and quantify spectral changes relevant for the interpretation of asteroidal spectral, including the common VisNIR range but also the mid-infrared range, now more accessible to remote-sensing observations than previously thanks to NASA JWST (e.g. [13]).

The irradiation and post-irradiation characterisation are scheduled to be concluded by July 2024. We will present first results of the irradiation experiments and further on-going efforts to describe the response of the samples to irradiation and phase-angle variations, crucial for the interpretation of remote-sensing observations of asteroids. Ultimately, the results obtained in this study will guide us in further constraining the nature of L-type asteroids by determining the closest analogue material within the meteorite collection and by aiding the interpretation of new spectra of L-type asteroids acquired in an on-going  observational campaign with ESO's VLT/X-SHOOTER as part of this project.

¹ The Loongana (CL) group is a recent addition to the taxonomy of chondrites [9].

References:
[1] Amelin, Y., et al. (2002), Science, 297, 1678
[2] Piralla, M., et al. (2023), Icarus, 394, 115427
[3] Burbine, T. H., et al. (1991), BAAS, 23, 1142
[4] Sunshine, J. M., et al. (2008), Science, 320, 514
[5] Scott, E. R. D. & A. N. Krot (2014),  In Meteor. and Cosmoch. Proc., 1, 65
[6] Devogèle, M., et al. (2018), Icarus, 304, 31
[7] Mahlke, M., et al. (2023), A&A, 676, A94
[8] Lantz, C., et al. (2017), Icarus, 285, 43-57
[9] Metzler, K., et al. (2021), GCA, 304, 1-31
[10] Potin, S.,  et al. (2018), Applied Optics, 57:8279, 2018
[11] Beck, P., et al. (2021), Icarus, 354, 114066
[12] Brunetto, R., et al., (2014), Icarus, 237:278-292, 7 2014
[13] De Kleer, K., et al. (2024), LPSC Abstract, 3040

Acknowledgements: This work was supported by the Programme National dePlanétologie (PNP) of CNRS-INSU co-funded by CNES.

How to cite: Mahlke, M., Aléon-Toppani, A., Lantz, C., Beck, P., Bonal, L., Brunetto, R., Tanga, P., and Aléon, J.: Analogues of enigmatic L-types: The effect of space weathering on CV, CO, CK, and CL chondrites, Europlanet Science Congress 2024, Berlin, Germany, 8–13 Sep 2024, EPSC2024-173, https://doi.org/10.5194/epsc2024-173, 2024.

Introduction
The study on the composition of meteorites, asteroids, comets, and trans-neptunian objects suggest that they contain materials originated during the early stages of the solar system formation. A relevant fraction of organic materials trapped in small bodies are thought to form from chemical reactions that involve carbon-bearing frozen volatiles species that are revealed in various star-forming regions and protoplanetary disks [1, 2]. Complex reactions are triggered by the interaction of solid-phase materials with energetic charged particles, such as galactic cosmic-rays (GCR), and energetic photons (x-rays, UV) that induce both the destruction of the pristine species and the formation of new compounds [3]. In addition, solar wind (SW) and solar energetic particles (SEP) also induce chemical reactions at the surface of outer icy small bodies [4]. As a result, pristine volatile species are destroyed and more complex molecules can form. The chemical complexity is further increased by the thermal processing that matter can suffer both during the star-formation process and in the event of migrations in the inner solar system. Processing at high temperature also affects the properties of meteorites during their entry into the atmosphere. Understanding how this event affects the physical, chemical, and spectral properties of meteorites is of particular relevance because these samples are often used to interpret the spectra of asteroids and other small bodies. 
Information on the chemistry triggered by energetic charged particles and heating in the formation of organic matter comes from laboratory experiments where simple carbon-bearing molecules are deposited at very low temperature (≤ 20 K), exposed to ion beams (keV-MeV), and further heated to room temperature (~ 300 K). These experiments lead to the formation of the so-called organic refractory residues, samples whose characterization revealed the presence of thousands of organic species, including compounds of astrobiological relevance, providing insights into the composition of extraterrestrial organics [5, 6, 7]. However, no information is available on the heating of organic refractory residues at temperatures higher than 300 K. 
Methods
We present new experiments of ion bombardment and further thermal heating of simple frozen volatile compounds representative of the pristine composition of icy materials in the presolar cloud. Ion bombardment experiments were performed with the facilities available at the Laboratory for Experimental Astrophysics (LASp) at INAF-Osservatorio Astrofisico di Catania (Italy). Ice mixtures containing H₂O, CH₃OH, NH₃ and CO, CH₄, and N₂ were deposited in a ultra-high vacuum chamber (P ≤10^-8 mbar) at low temperature (18 K) and exposed to 200 keV H⁺ and He⁺, respectively. After the bombardment, processed ices were warmed-up to 300 K with a constant heating rate in order to produce organic refractory residues. These samples were then extracted from the UHV chamber, stored in vacuum sample holders and transferred to the Planetary Spectroscopy Laboratory (PSL) at the DLR Berlin. At the PSL, organic refractory residues were placed in a oven and heated in vacuum (P≤10^-2 mbar) up to 970 K. The heating was performed in various step and with a constant heating rate.
During the ion bombardment, samples were analysed by means of Fourier-transform infrared (FT-IR) spectroscopy in the near- and mid-IR (1.25-10.5 µm, 8000-950 cm^-1) in transmittance mode. Several spectra were acquired in-situ during the processing, allowing us to follow the changes induced by energetic charged particles in the composition of ices. Spectra were also acquired during the warm-up to 300 K to follow the formation of organic refractory residues. At the PSL, FT-IR spectroscopy was also used to characterize samples after each step of warm-up.
Results
The spectra collected during ion bombardment at 18 K show the destruction of the pristine frozen compounds and the formation of new species, including the precursors of complex organic species, such as aldehydes (5.81 µm, 1720 cm^-1) and CN-bearing compounds (4.42 µm, 2260 cm^-1). The characterization performed after ion bombardment and during warm-up to 300 K show the sublimation of the most volatile species and spectral changes that point to the formation of organic refractory materials, as reported in previous similar experiments [8]. 
The further heating performed at the DLR shows relevant changes in the spectral properties of samples. In all cases, we observed a decrease in the intensity of the signal that is associated to a loss of material during warm-up. Shifts in the band position and changes in the relative intensity of absorption features also testify the alteration of the chemical properties of samples. In particular, we reveal strong changes in the 5.8-6.8 µm (1720-1470 cm^-1) region that includes the absorption features of C=C, C=O, and C=N bearing compounds as well as in the region around 4.5 µm (2200 cm^-1) that contains the absorption features of nitriles.
The data obtained are used to interpret the IR spectra of organic-rich meteorites and will support the understanding of the alteration induced by thermal processing of organic-rich surfaces in the inner solar system. 
Acknowledgements
This work is supported by  the Istituto Nazionale di Astrofisica (INAF) through the grant Organic Refractories Sustaining microOrganisms - ORSO, CUP C63C23001250005. RGU acknowledges the support from the Società Italiana di Scienze Planetarie - Angioletta Coradini (SISP-AC).

References
[1] McClure, M. K., Rocha, W. R. M., Pontoppidan, K. M. et al. 2023, Nat. Astronomy, 7, 431
[2] Sturm, A. J., McClure, M. K., Beck, T. L. et al. 2023, A&A, 679, A138
[3] Rothard, H., Domaracka, A., Boduch, P., et al. 2017, J. Phys. B, 50, 062011
[4] Urso, R. G., Vuitton, V., Danger, G. et al. 2020, A&A, 644, A115
[5] Nuevo, M., Auger, G., Blanot, D., & D’Hendecourt, L. 2008, Orig. Life Evol. Biosph., 38, 37
[6] Meinert, C., Myrgorodska, I., de Marcellus, P., et al. 2016, Science, 352, 208
[7] Danger, G., Orthous-Daunay, F. R., de Marcellus, P., et al. 2013, Geochim. Cosmochim. Acta, 118, 184
[8] Baratta, G. A., Chaput, D., Cottin, H., et al. 2015, Planet. Space Sci., 118, 211

How to cite: Urso, R. G., Alemanno, G., Baratta, G. A., Burr, D., Cadelli, E., Elsaesser, A., Helbert, J., Maturilli, A., Occhipinti, G., Palumbo, M. E., and Scirè, C.: Spectral changes induced by thermal processing of organic refractory materials, Europlanet Science Congress 2024, Berlin, Germany, 8–13 Sep 2024, EPSC2024-800, https://doi.org/10.5194/epsc2024-800, 2024.

Introduction:

The main-belt comets (MBCs) are objects that exhibit cometary activity but occupy stable orbits in the main asteroid belt. MBCs are considered as a hidden reservoir of water ice in the Solar System, and have the potential in terms of scientific research and space resource utilization in the future (Hsieh, 2020). The main-belt comet 133P/Elst-Pizarro (133P) is the first discovered  and best characterized member of the MBCs. Dynamically, 133P fits well in Themis asteroid family (Hsieh et al., 2004). The spectra of 133P resembles best of B-type asteroid and is very similar to those of Themis family members (Hsieh et al., 2008; Licandro et al., 2011). Meteorites that can be compared to the Themis family are CI, CM, CR, CI-unusual, and CM-unusual (Clark et al., 2010).

This abstract described a series of methods to manufacture ice-bearing regolith simulant samples for 133P in the laboratory. The characteristics of the analogue are also obtained. The methods in this work can also be applied to the preparation and application of surface regolith simulants of other icy celestial bodies in the Solar System, which can provide scientific basis and ground truth for remote sensing detection, landing sampling and in-situ resource utilization in future probes.

Method:

The study involved creating a surface material analogue based on the observed and modeled composition of 133P. The surface regolith of the cometary is mainly composed of water ice, refractory organic matter, and minerals. A basic recipe for the prototype analogue is based on the observation and compositional modeling spectrum of 133P (Rousselot et al., 2011) and the modal mineralogy of the related meteorites. The analogue was developed using a mix of water ice, silicates (serpentine, olivine, pyroxene), amorphous carbon, and organics. Two methods were employed for preparing the ice-dust mixtures:

Mixing pre-prepared micron-sized ice particles with comet surface soil mimic powder in a cryogenic freezer.

Adding the cometary dust simulant to a dewar with generated ice particles, then separating the mixture after liquid nitrogen volatilization.

Fig. 1 Cometary surface regolith ice-dust analogue according to method 1

Fig. 2 Cometary surface regolith ice-dust analogue according to method 2

Characterization of the analogue included optical microscopy for morphology and particle size, laser diffraction for particle size distribution, X-ray fluorescence (XRF) spectrometry for bulk chemistry, and spectrophotometric analysis for optical properties.

Results:

The developed analogue successfully mimics the surface regolith of 133P. Optical microscopy revealed that the water ice particles were spherical, ranging from 2-12 μm. Laser diffraction indicated a broad particle size distribution, with the majority of particles falling within the expected size range for cometary dust. XRF spectrometry confirmed that the major elemental composition of the analogue closely matches that of carbonaceous chondrites, specifically CO3 chondrites, which are considered analogues for cometary material. Spectrophotometric analysis showed that the analogue's spectrum aligned well with observed data for 133P, validating the compositional accuracy of the analogue.

Fig.3 Spectrum of the cometary material analogue (red line); visible spectrum of 133P reported by Licandro et al. (2011, yellow spots); near-infrared spectrum of 133P reported by Rousselot et al. (2011, blue spots).

Conclusion:

 Our cometary analogue provides a robust foundation for simulating cometary processes such as sublimation, deposition, and irradiation, crucial for understanding the early Solar System. Additionally, it supports the development of technologies for future space missions, including sample return missions and in-situ resource utilization.

References:

Hsieh, Henry. "Active Asteroids: Recent Results and Future Prospects." 44th COSPAR Scientific Assembly. Held 16-24 July 44 (2022): 200.

Licandro, J., et al. "Testing the comet nature of main belt comets. The spectra of 133P/Elst-Pizarro and 176P/LINEAR." Astronomy & Astrophysics 532 (2011): A65.

Clark, Beth Ellen, et al. "Spectroscopy of B‐type asteroids: Subgroups and meteorite analogs." Journal of Geophysical Research: Planets 115.E6 (2010).

Rousselot, Philippe, Christophe Dumas, and Frédéric Merlin. "Near-infrared spectroscopy of 133P/Elst-Pizarro." Icarus 211.1 (2011): 553-558.

How to cite: Zhang, X. and Xiao, Y.: Development of surface materials analogues of the main-belt comet 133P/Elst-Pizarro, Europlanet Science Congress 2024, Berlin, Germany, 8–13 Sep 2024, EPSC2024-1214, https://doi.org/10.5194/epsc2024-1214, 2024.

Introduction.

Comparing ultraviolet (UV) -visible (Vis) -infrared (IR) spectra of terrestrial/extraterrestrial materials with asteroids and moons is important to estimate surface mineralogical and physicochemial properties, which can provide clues to reveal the formation and evolution processes of the Solar System. This presentation reviews two topics of our current findings related to spectral comparison between remote-sensing and laboratory measurements for the asteroid Ryugu and the Moon, that will be useful for future in-space small body observations and sample return missions including MMX.

Comparison between lab-measured and remote-sensed spectra of Ryugu.

C-class asteroids are thought to be primitive bodies recording the solar system formation process. Captured samples have been delivered from the near-Earth asteroid (162173) Ryugu by the JAXA's Hayabusa2 spacecraft in 2020. Based on the results obtained by initial sample analyses, captured Ryugu materials are representative of Ryugu body surface, which has been aqueously altered strongly, and most similar to CI (Ivuna-type) chondrites spectroscopically and chemically [1-5]. In a spectroscopic view, however, there is a gap between remote-sensed data and lab-measured data. Lab-measured reflectance spectra of Ryugu samples in multiple grain and powder forms show a weaker OH absorption band at 2.7 μm due to hydrous silicates. Comparison among lab Ryugu spectra and carbonaceous chondrite spectra with different grain size, porosity, and space-weathering degree reproduced by ion/laser-irradiation experiments was performed, indicating that space weathering due to micrometeoroid bombardments mainly promotes spectral change at the Ryugu's surface [6].

Lab-measured spectra of ilmenite implication for the Moon.

Clarifying the distribution and abundance of ilmenite (FeTiO₃) on the Moon is important for elucidating the formation and evolution process of the Moon and the property of the magma ocean. Ilmenite is abundant in the lunar mare basalts, and thus spectral properties of ilmenite in the UV-Vis-IR range have been investigated and known to show a positive peak at around 1 μm as a remnant of two neighbor absorption bands centered at around 630 nm and around 1300 nm due to Ti³⁺-Ti⁴⁺ charge transfer and Fe²⁺ crystal field transitions, respectively (e.g., [7] and referenses therein). Lunar spectra observed by the Spectral Profiler on board Kaguya/SELENE show a slight rise was found near the peak of 1 μm band absorption on the surface of the moon, and it was coincidently detected by the Multiband Imager [8]. Previous ground-based telescope obsevations also showed a weak rise inside 1 μm absorption band in the areas called Taurus-Littrow and Rima Bode on the lunar surface [9].  Ilmenite is thought to coexist with other minerals, therefore, Matsuoka and Yamamoto (2024) [10] performed lab spectral measurements using powdered ilmenite samples and other possible components of lunar basalts, e.g., augite and glass, with various mixing ratio. They reported that a little amount of ilmenite powder may produce absorption bands causing the 1-μm peak, and strong darkening, In contrast, significant blue slope (decreasing toward longer wavelength) in the UV range of ilmenite rapidly masked by a small amount of glass component, making the UV slope redder. It is suggested that to investigate ilmenite, using the UV feature gives very limited information on the lunar surface as considered by Sato et al. (2017) [11]. Those complex UV-Vis-IR spectral characteristics are necessary to be considered to interpret remote-sensed data based on quantitative data obtained by lab measurements.

Considering each of the component minerals has a different effect on reflectance spectra, while also unique alteration process and characteristics in space environments such as space weathering, suggests that sample return and close observations of Phobos, similar to D-type asteroids but whose surface properties are still unvailed, will provide a new property of the in-space surface characteristics of small bodies by MMX mission [12].

References:
[1] Tachibana et al. (2022) Science 375, 1011–1016.
[2] Pilorget, C. et al. (2022) Nat. Astron. 6, 221–225.
[3] Yada et al. (2022) Nat. Astron. 6, 214–220.
[4] Yokoyama et al. (2022) Science 379, eabn7850
[5] Nakamura et al. (2022) Science 379, eabn8671.
[6] Matsuoka et al. (2023) Commun Earth Environ 4, 335.
[7] Iwaza et al. (2021) Icarus, 362, 114423.
[8] Yamamoto et al. (2023) Fall Lecture of the Society of Planetary Sciences.
[9] Gaddis et al. (1985） Icarus, 61, 3, 461-489.
[10] Matsuoka and Yamamoto.(2024) Japan Geoscience Union Meeting 2024, PPS09-P01
[11] Sato et al. (2017) Icarus, 296, 216–238.
[12] Kuramoto et al. (2021) Earth, Planets and Space, 74:12.

How to cite: Matsuoka, M.: Investigating reflectance spectra to link remote-sensed data with lab-measured data: cases of asteroid (162173) Ryugu and the Moon, Europlanet Science Congress 2024, Berlin, Germany, 8–13 Sep 2024, EPSC2024-1290, https://doi.org/10.5194/epsc2024-1290, 2024.

Comets and asteroids are among the most pristine objects in the Solar System, being formed out of the materials available in the proto-Solar Nebula [1]. Especially interesting are the complex organic molecules in these bodies, as they likely contribute towards the elemental composition of forming planets, as well as potentially being delivered after accretion of planetary bodies via impacts and thus contribute to their molecular inventory [2, 3].

Many primitive solar system objects, such as carbonaceous chondrites or interplanetary dust particles (IDPs), contain organic matter, which itself can be divided into a solvent-soluble (soluble organic matter, SOM) and insoluble fraction (Insoluble Organic Matter, IOM) [4, 5]. The soluble fraction can contain PAHs, sugars, nucleobases, and amino acids [6, 7, 8, 9]. The insoluble fraction is a mix of large macromolecules with numerous molecular links and functional groups [3, 14]. The formation environment of the IOM is an area of ongoing research and IOM could have formed either in the interstellar medium or in the proto-Solar Nebula [3].

In the proto-Solar Nebula, interstellar space, and protoplanetary disks, microscopic ice-coated dust grains are readily available. Laboratory experiments on the energetic processing of extraterrestrial and interstellar ice analogues show that a number of complex molecules form, including prebiotic molecules [e.g., 10, 11, 12, 13, 14], therefore focussing on recreating the chemical inventory observed in SOM. Even though it makes up the majority of the organic carbon in solar system objects, IOM has not been extensively studied in the laboratory. However, the formation pathways of IOM are crucial to understand the complex – insoluble – organic molecules available for the formation of planetary bodies.

Methods

In this study, irradiation experiments on ice are performed with the ICEBEAR setup [15]. The setup consists of a stainless-steel vacuum chamber with base pressures of <2∗10^-8 mbar. Vacuum-grade aluminium foil is fixed onto a copper sample holder (Fig. 1), which is mounted on the cold head of a closed cycle helium cryostat, allowing for cooling of the sample holder to < 5 K. The temperature of the sample holder is monitored using a diode and two heating elements are mounted into the sample holder to allow for resistive heating. In a separate gas mixing system, gases are mixed and enter the chamber via a manually operated leak valve. This results in the formation of a simulated extraterrestrial ice film on the aluminium foil.

For the ices investigated in this study, H₂O, CH₃OH and N₂ are used. H₂O is the main constituent of interstellar ices, with CH₃OH being a major ice component in various astrophysically relevant objects and acting as a carbon donor. N₂ is used as a proxy for abundant nitrogen donors, such as ammonia.

The gas mixture is leaked into the chamber, where it adsorbs onto the cold (~10 K) aluminium foil. Next, the ice is irradiated with 5 keV electrons, resulting in the formation of soluble organic matter. For several samples, a second irradiation is performed, which has been observed to lead to the formation of a darker residue, presumed to be insoluble organic matter. Different experimental procedures, including the parameter space of temperatures and irradiation durations and their influence on the resulting residues are investigated.

The produced residues are analysed using micro-Raman spectroscopy at ETH Zürich with a laser operating at 532 nm. Raman spectroscopy is a powerful tool to investigate the structure of carbonaceous material. Especially interesting are the D (disordered) and G (graphite) bands of carbon. The peak widths and positions of the two bands, as well as their ratio, give valuable information about the structural order of the material. The results are compared to IDPs, which are thought to contain some of the most primitive organic matter in the solar system [5].

Results:

The initial analysis of the residue of a double irradiated ice sample with micro-Raman spectroscopy hints towards the formation of amorphous carbon that is even more primitive than the IOM observed in meteorites and rather resembles the IOM extracted from IDPs.

Further analysis is needed to show the evolution of the Raman spectra as a function of the investigated parameters. The ongoing work will be presented and the influence of different laboratory conditions on the resulting residue investigated. This investigation helps bridge the gap between the parent ices as building blocks of organic material in meteorites and comets and the observed structure of primitive meteorites.

References:

[1] Caselli & Ceccarelli, Astron Astrophys Rev 20, 2012, doi : 10.1007/s00159-012-0056-x

[2] Chyba & Sagan , Nature, 1992, doi: 10.1038/355125a0

[3] Alexander et al. Geochemistry, 2017, doi: 10.1016/j.chemer.2017.01.007

[4] Garcia et al., ACS Earth and Space Chemistry, 2024. doi: 10.1021/acsearthspacechem.3c00366

[5] Riebe et al., Earth and Planetary Science Letters, 2020, doi: 10.1016/j.epsl.2020.11626

[6] Pizzarello et al., Meteorites and the Early Solar System II, 2006

[7] Callahan et al., Proceedings of the National Academy of Sciences,  2011, doi: 10.1073/pnas.1106493108

[8] Furukawa et al., Proceedings of the National Academy of Sciences, 2019, doi: 10.1073/pnas.1907169116

[9] Lecasble et al., Geochim. Cosmochim. Acta 2022, doi: 10.1016/j.gca.2022.08.039

[10] Allamandola et al. Space science reviews, 1999, doi:  10.1023/A:1005210417396

[11] Herbst & van Dishoeck, Annual Review of Astronomy and Astrophysics, 2009, doi:10.1146/annurev-astro-082708-101654

[12] Öberg, Chemical Reviews, 2016, doi: 10.1021/acs.chemrev.5b00694

[13] Muñoz Caro et al., ACS Earth and Space Chemistry, 2019, doi: 10.1021/acsearthspacechem.9b00086

[14] Danger et al., A&A, 2022, doi : 10.1051/0004-6361/202244191

[15] Kipfer et al., Icarus, 2024, doi: 10.1016/j.icarus.2023.115742

How to cite: Kipfer, K., Ligterink, N. F. W., Riebe, M., and Allen, N. M.: The origin of Insoluble Organic Matter: Formation of macromolecules from heavily irradiated simple ices, Europlanet Science Congress 2024, Berlin, Germany, 8–13 Sep 2024, EPSC2024-176, https://doi.org/10.5194/epsc2024-176, 2024.

Introduction

The pathways from simple organic molecules to prebiotics and complex life on Earth remain poorly understood. Adenine and other organic compounds involved in biochemistry have been detected in carbonaceous chondrites and laboratory analogs of Titan aerosols (Hayatsu et al., 1964; Martins et al., 2008; Pilling et al., 2009). Laboratory experiments propose abiotic nucleic base formation in various space environments (Sebree et al., 2018; Kimura and Kitadai, 2015; Gupta et al., 2011). Radiation exposure in space raises questions about adenine's stability under ionizing radiation, as it is an essential component of DNA. Previous studies investigated solid adenine's survivability under different radiation sources such as high energy representatives of galactic cosmic rays (Huang et al., 2014; Peeters et al., 2003; Poch et al., 2014; Evans et al., 2011). Here, ions are more representative of the solar wind. Higher energy radiation leads to adenine destruction and formation of smaller molecules or ions (Peeters et al., 2003). However, adenine exhibits higher photostability compared to other compounds under low-energy UV-radiation, indicating the formation of more complex molecules protecting it from further destruction (Poch et al., 2014).  This study explores the effects of irradiating solid adenine thin films with 30 to 70 keV ¹⁸O⁺- and ²⁰Ne⁺-ions, an energy range not thoroughly investigated previously (Huang et al., 2014). In-situ IR-spectroscopy and ex-situ ultra-high-resolution mass spectrometry (HRMS) provide insight into spectral and chemical properties, focusing on the chemical analysis of the higher mass ranges.

Experimental Methodology

Two methods were used for the sample synthesis. Firstly, at Institut de Planétologie et d'Astrophysique de Grenoble (IPAG), adenine powder was dissolved in an ethanol-water solution and deposited onto MgF₂ windows, resulting in "grainy" films. Secondly, at Laboratoire Interuniversitaire des Systèmes Atmospheriques (LISA), sublimation/ recondensation reactor produced homogeneous "thin-films" on MgF₂ windows at 130 °C under 2.0x10^-3 mbar pressure. The irradiation experiments were conducted at GANIL (Caen) and IJCLab (Orsay) using ¹⁸O⁺ and ²⁰Ne⁺-ion beams. In total, 17 adenine samples underwent irradiation with energies ranging from 30 to 70 keV. Ion flux and total fluence varied, with some samples cooled to 150 K for comparison purposes. IR spectra were recorded during irradiation. Finally, in the ex-situ analysis phase, the chemical composition was determined using the ultra-high-resolution mass spectrometer Orbitrap. The soluble parts of samples were analyzed via Electrospray Ionization (ESI) in negative mode. The mass spectra were interpreted using an in-house program (ATTRIBUTOR). There, molecular ions are attributed to each individual mass peak.

Results and Conclusions

The results show that low energy ion irradiation of adenine leads not only to its destruction but also to the formation of larger molecules following (HCN)𝑥R, where x ≤ 14. These HCN-molecules show a great chemical diversity and complexity with R being C𝑥, H𝑥, N𝑥, N𝑥H𝑦, C𝑥H𝑦 or C𝑥N𝑦, with the latter being the most versatile. New appearing bands in the IR-spectra indicate the formation of nitriles, primary amines and CN ring bonds. The aromaticity equivalent (Xc) of the HCN-molecules reveals their structure:

Xc = ((C#-((H#-N#)-C#))/DBE)+1    (1)

where C#, H# and N# is the number of carbon, hydrogen and nitrogen atoms in the molecule and DBE is the double bond equivalent. Yassine et al. (2014) propose a threshold value of Xc ≥ 2.5 for the presence of aromatic structures and Xc ≥ 2.7143 for condensed aromatic structures or polycyclic aromatic nitrogen bearing hydrocarbons (PANH) (s. Figure 1). Due to the degree of aromatization, a repeating ring structure as shown in Figure 1 is likely.

The free parameters (ion, energy, temperature) of the irradiation experiment do not have a noticeable influence on the chemical complexity of the samples. Furthermore, nitrogen is very efficiently incorporated into the new forming molecules of the irradiated adenine samples.

Figure 1: The aromaticity equivalent (Xc) as a function of number of carbon atoms (C#) for the molecules in the irradiated adenine samples. The size of the circles corresponds to the normalized intensity of the molecule in the mass spectrum (left). Schematic chemical structure versions of HCN-polymer from Völker (1960) (right).

Acknowledgements

We thank the Programme National de Planétologie (PNP) for supporting this work. This work is supported by the French National Research Agency in the framework of the "Investissements d’avenir” program (ANR-15-IDEX-02) and the generic call for proposals (ANR-22-CE49- 0017). The experiments were performed at the Grand Accélérateur National d’Ions Lourds (GANIL) by means of the CIRIL Interdisciplinary Platform, part of CIMAP laboratory, Caen, France. We thank the staff of CIMAP-CIRIL and GANIL for their invaluable support. We acknowledge the fundings from ANR IGLIAS grant ANR-13-BS05-0004 of the French Agence Nationale de la Recherche.

References

• Evans, Nicholas L., et al. "On the interaction of adenine with ionizing radiation: Mechanistical studies and astrobiological implications." The Astrophysical Journal 730.2 (2011): 69.
• Gupta, V. P., et al. "Quantum chemical study of a new reaction pathway for the adenine formation in the interstellar space." Astronomy & Astrophysics 528 (2011): A129.
• Hayatsu, Ryoichi. "Orgueil meteorite: organic nitrogen contents." Science 146.3649 (1964): 1291-1293.
• Huang, Qing, et al. "Quantitative assessment of the ion-beam irradiation induced direct damage of nucleic acid bases through FTIR spectroscopy." Nuclear Instruments and Methods in Physics Research Section B: Beam Interactions with Materials and Atoms 330 (2014): 47-54.
• Kimura, Jun, and Norio Kitadai. "Polymerization of building blocks of life on Europa and other icy moons." Astrobiology 15.6 (2015): 430-441.
• Martins, Zita, et al. "Extraterrestrial nucleobases in the Murchison meteorite." Earth and planetary science Letters 270.1-2 (2008): 130-136.
• Peeters, Z., et al. "The astrobiology of nucleobases." The Astrophysical Journal 593.2 (2003): L129.
• Pilling, Sergio, et al. "DNA nucleobase synthesis at Titan atmosphere analog by soft X-rays." The Journal of Physical Chemistry A 113.42 (2009): 11161-11166.
• Poch, O., et al. "Laboratory insights into the chemical and kinetic evolution of several organic molecules under simulated Mars surface UV radiation conditions." Icarus 242 (2014): 50-63.
• Sebree, Joshua A., et al. "Detection of prebiotic molecules in plasma and photochemical aerosol analogs using GC/MS/MS techniques." The Astrophysical Journal 865.2 (2018): 133.
• Völker, Th. "Polymere blausäure." Angewandte Chemie 72.11 (1960): 379-384.
• Yassine, Mahmoud M., et al. "Structural characterization of organic aerosol using Fourier transform ion cyclotron resonance mass spectrometry: aromaticity equivalent approach." Rapid Communications in Mass Spectrometry 28.22 (2014): 2445-2454.

How to cite: Matuszewski, F., Vuitton, V., Shouse, J., Launois, T., Chaouche, N., Flandinet, L., Quirico, E., Brunetto, R., Boduch, P., Domaracka, A., Rothard, H., Stalport, F., Orthous-Daunay, F.-R., and Cottin, H.: Ion induced formation of complex HCN-species in solid-phase adenine, Europlanet Science Congress 2024, Berlin, Germany, 8–13 Sep 2024, EPSC2024-341, https://doi.org/10.5194/epsc2024-341, 2024.

Because life evolved as an asymmetric phenomenon, any comprehensive theory of its emergence on Earth must explain the origin of biological homochirality—the predominant presence of specific chiral configurations in biopolymers, such as d-sugars in nucleic acids (DNA and RNA) and l-amino acids in proteins. The systematic reports of an excess of l-amino acids in several carbonaceous meteorites prompted the hypothesis that interstellar chemistry may have played a role in the origin of homochiral biomolecules by biasing the presumably racemic abiotic pool on early Earth through the delivery of extraterrestrial debris containing enantioenriched molecules [1]. Asymmetric photochemistry by circularly polarized light (CPL) constitutes the leading explanation for the observed l-excesses of amino acids in meteorites due to its proved capability of inducing enantiomeric excesses (ee) in amino acids via asymmetric photolysis [2] and the discovery of CP radiation in infrared star-forming regions [3].

However, recent findings concerning the enantioselective analyses of amino acids from asteroid Ryugu [4], and more recently, from asteroid Bennu [5], seem to contradict the CPL scenario. All amino acids found in these pristine samples, which theoretically should be free from terrestrial contamination, have been reported as racemic. We aim to challenge these findings by comparing them with the results of our comprehensive methodology for the reliable enantioselective analyses of extra-terrestrial chiral amino acids. Our study focuses on the Orgueil meteorite, a CI chondrite known to resemble the mineralogy and amino acid composition of the asteroid Ryugu [6]. We propose that the observed racemic contents in Ryugu, and possibly Bennu, could potentially stem from the limited quantity of samples analysed and the resulting constraints in the reliability of the available analytical methodologies. This limitation, especially in accurately quantifying small ees (<5%) [7], as those expected to be produced by CPL asymmetric photolysis [2], could contribute to the reported results.

Robust enantioselective methodologies combining high sensitivity, resolution, and reliable determination of small ees are decisive to understand the distribution and characteristics of chiral compounds in astro-physical samples, as well as comprehending the potential role of symmetry-breaking interstellar processes. In our investigation, we focussed on minimizing degradation and racemization processes throughout all stages of the extraction-chromatographic protocol. Particular attention was devoted towards assessing and reducing the impact of the mineral matrix, as well as minimizing potential contamination sources. Through analysing several fragments of the Orgueil meteorite, we will highlight the critical impact of analyte concentration, enantiomeric resolution, and a rigorous statistical treatment of the chromatographic data to reduce quantification uncertainties when measuring and reporting ees.

References

• [1] Glavin D. P., et al. Rev. 120, 4660–4689 (2020)
• [2] a) Meinert, C., et al. Chem. Int. Ed. 53, 210 (2014); b) Bocková, J., et al. Nat. Commun. 14, 3381 (2023)
• [3] a) Bailey J., et al. Science 281, 672–674 (1998); b) Chrysostomou A., et al. Nature 450, 71–73 (2000), c) Kwon J., et al. J. Lett. 765, L6 (2013).
• [4] a) Naraoka H. et al., Science 379, eabn9033 (2023). b) Parker E.T. et al. Cosmochim. Acta, 347, 42–57 (2023)
• [5] Glavin D. P., et al. 55th Lunar and Planetary Science Conference (LPSC), 1640 (2024)
• [6] Yokoyama T., et al., Science 379, eabn7850 (2023).
• [7] Pepino R., Sep. Sci. 45, 4416–4426 (2022).

Acknowledgement: Supported by the European Research Council under the European Union’s Horizon 2020 research and innovation programme [grant agreement 804144].

How to cite: Leyva, V., Robert, M., Bocková, J., and Meinert, C.: Challenging the racemic amino acid content of asteroid Ryugu through the reliable enantioselective analysis of the Orgueil meteorite, Europlanet Science Congress 2024, Berlin, Germany, 8–13 Sep 2024, EPSC2024-773, https://doi.org/10.5194/epsc2024-773, 2024.

Introduction
Mass wasting is one of the most prevalent geomorphological processes contributing to surface evolution
across the Solar system [Moore et al. (1999); Roelofs et al. (2024)]. It is the downslope movement of
fine material (e.g., regolith) and granular material (e.g., rock debris) under the influence of gravity
seen in e.g., falls, slides, avalanches or flows. Identifying the
formative processes of mass-wasting can give us insights into the distribution of volatiles across the
Solar System which is important for future space missions [Parekh et al. (2021)]. Using terrestrial mass-wasting deposits as
analogues is useful with limitations [Scully et al. (2015)]. In contrast to Earth, on other planetary surfaces, water is at best metastable (i.e., boiling, sublimating and/or freezing). 
While sublimation is a plausible surface process on some planetary bodies [Mangold (2011); Roelofs
et al. (2024)], it cannot be studied on Earth. Here we address this critical gap in our knowledge
of the mobility, morphology and evolution of sublimation-driven mass flows through laboratory-scale
experiments.
Sublimating ice causes gas to flow through granular material, reducing internal friction and enhancing the flow’s mobility. The velocity of the gas expansion depends on gas density and the material's permeability, regardless of gravity. However,
the force needed to lift the sediment particles with a given density is proportional to the gravitational
acceleration. Aspects of the effects of gravity on the morphology, mobility and dynamics of dry and
liquid-based mass-wasting have been studied (Kleinhans et al. (2011); Kokelaar et al. (2017)) but
remain poorly understood in sublimation-driven mass-wasting.
Here we study the role of gravity in sublimation-driven mass-wasting with
a set of experimental debris flows in a low-pressure chamber. We analyse the dynamics, morphology,
mobility, and fluidization of CO2-sublimation-driven mass granular flows under various atmospheric
pressures and sediments with varying densities.

Methods
The laboratory simulations were performed in a debris flow flume in a
cylindrical low-pressure Mars chamber of the Space and Planetary Environments Laboratory at the
Open University (Milton Keynes, UK). The debris flow is initiated from a sediment-ice reservoir atop a chute and runs out on an outflow plain (Figure 1). The downstream part of the chute is instrumented with two relative gas pressure
sensors to measure the overpressure (differential gas pressure,
i.e. gas flow pressure relative to the ambient pressure), a geophone to record seismic vibrations, a load cell to record the weight of the granular flow and three laser range sensors to capture the flow depth. Moreover, we used
a Phantom Miro C110 high-speed camera to capture the movement of the flow and the individual
particles.

Figure 1: The laboratory debris flow flume in the Mars chamber at the Space and Planetary Environments Laboratory at the Open University (UK). (a-b) display the chute including the instruments and the sediment-ice reservoir. (c) shows the entire flume looking upslope.

To represent atmospheric pressures on different planetary bodies, we applied a range of pressures
between 3 to 1000 mbar. The granular flows were simulated by mixing dry CO2 ice with granular materials to create sediment mixtures with different permeabilities and densities.
Two groups with angular sediments (quarry sand and walnut shells) and rounded sediments (solid and
hollow glass beads) were chosen so that we could also determine the effects of the sediments’ shape
on the granular flows. To assess the effect of lower gravity, each group has a higher-density sediment
used as reference (quarry sand of 2600 kg/m3 and solid glass beads of 2500 kg/m3
), and a lower-density sediment (crushed nutshell of 1300 kg/m3 and hollow glass beads of 410 kg/m3
). The particle distribution for the angular sediment was similar for all sediment mixtures and fixed to 25% fine (200 -
450 µm), 50% medium (450 - 800 µm) and 25% coarse (800 - 1300 µm). The rounded sediment had a
particle size range between 500 - 850 µm. Gravitational acceleration and density have the same effect
on the force needed to levitate the flowing sediment. Thus, to simulate low-gravity bodies, we utilize
low-density sediments.

Results and discussion
Our preliminary results reveal an overall increase in fluidization of the granular flows for decreasing
pressures. This is more prominent in the low-density sediments. At 3-10 mbar, we notice a
fluidization regime similar to bubbling, where the CO2 gas builds up in the flow and escapes following
a small outburst [Van Ommen et al. (2010)].

Figure 2: (a) frontal flow velocities, (b) overpressure: the ratio of the maximum
differential pore pressure (difference between basal and ambient pressure) vs. ambient pressure and
(c) runout: the H/L ratio of all the sediments.

The enhanced fluidization at low pressures is also apparent in the increased frontal flow velocities,
increased overpressure and increased runout length (H/L ratio, where H is 0.43 m and L is runout
length) (Figure 2). The internal pore pressure increases relative to ambient pressure (Figure 2b) which
decreases the internal particle friction and enhances the flow’s velocity (Figure 2c).
The levitation effect is observed here as increasing flow depth for decreasing pressures. This confirms the prior hypothesis that, at low ambient pressures, the gas outflux from sublimating CO2 ices increases, which levitates the sediment particles and reduces intergranular friction and particle
collisions [de Haas et al. (2019); Roelofs et al. (2024)].

Conclusion
Experiments have been performed to study the effects of gravity by mixing CO2 ice and granular
material with different permeabilities and densities. Low-density sediments, representing lower gravity,
display a longer deposit runout and higher frontal flow velocities and flow depths compared to high-density sediments. At low atmospheric pressures (3-10 mbar), we observe a transition in the
flow behaviour known as turbulent bubbling in the low-density sediments. These findings show that
atmospheric conditions and gravity on different planetary bodies lead to changes in the mobility and
flow behaviour of granular flows, which may be observable in the deposit dimensions. Further analyses
will focus on PIV data to study the appearance of bubbling at low pressures in more detail and elevation
models of the deposits from imagery to study their morphology.

How to cite: Diamant, S., Sylvest, M., Conway, S., Roelofs, L., Emerland, Z., Patel, M., Kleinhans, M., and de Haas, T.: Effects of gravity in CO2-sublimation driven granular flows in a simulated experimental environment, Europlanet Science Congress 2024, Berlin, Germany, 8–13 Sep 2024, EPSC2024-399, https://doi.org/10.5194/epsc2024-399, 2024.

Introduction

Silicates are the main constituent of volcanic terrains on terrestrial planets in the Solar system. On Earth, we know that volcanic terrains are constituted by lava flows and fragmented pyroclasts whose texture presents both glassy and crystalline phases. Understanding the influence of glass/crystal ratio on the spectral response of volcanic rocks is therefore focal to interpret remotely sensed spectra that are commonly used to interpret the geology of terrestrial planets. Thus, we performed spectral characterization of lab-made mafic volcanic products which were synthesized in the petro-vulcanology research group (PVRG) labs to present different degrees of crystallinity.

Samples preparation and characterization

Samples were created by mixing powdered oxides to mimic the composition of a Nakhlite meteorite. The powder was melted at 1450°C to form a silicate melt, which was then quickly cooled to produce a glass and divided into four sub-samples. As observable in Fig. 1, one sub-sample was rapidly cooled in air to form Nglass, while the other three were slowly cooled (52-60°C per hour) to target temperatures of approximately 1200°C (N12), 1100°C (N11), and 1000°C (N10).

Figure 1: Cooling ramps for the syntheses of products with different crystallization degree

The synthesized samples were analyzed using X-ray powder diffraction (XRPD), and quantitative phase analysis (QPA) was performed using the Rietveld profile fitting method with internal standards to determine amorphous content. Crystallized samples (N10, N11, and N12) showed peaks corresponding to various crystalline phases including Augite, Cristobalite, Magnetite, and Hematite. Quantitative analyses are reported in as reported in Figure 2.

Figure 2: Mineralogical assemblage of the produced samples

Reflectance analysis

Spectroscopic characterization was performed with SHINE (SpectropHotometer with variable INcidence and Emergence) at the Cold Surface Spectroscopy facility (CSS) of IPAG laboratory. This setup allows the collection of spectra in the visible (VIS) and near-infrared (NIR) ranges (0.35–4.5 µm) across a broad range of illumination (0–30°) and emergence angles (e=0-70°) at room temperature. Both illumination and emergence angles are zenithal angles, measured from the normal direction to the surface. Approximately 2 g of powdered samples (grain size < 80 µm). All acquired spectra are shown in Figure 3 where they are divided in four subgraphs representing the four samples N10, N11, N12 and Nglass.

Figure 3: VNIR spectra of four samples at different acquisition geometries.

Principal component analyses (PCA)

Our set of spectra was analyzed using PCA and K-Means clustering to visualize differences and similarities between the spectra from an unsupervised machine learning perspective. Principal component analysis was then performed without normalization, retaining the first two PCs, which encompass ~99.82% of the total variance (Figure 3a). The elbow method was used to determine the optimal number of clusters, resulting in 3 clusters (Figure 4). This led to a well-defined classification with only 3 misclassified samples. The mean spectra from each cluster were visibly similar to the spectra of each class, with low standard deviation for Nglass and N12, and higher for the cluster comprising N10 and N11. The resulting PCs are explainable from the loadings, showing that the first PC mainly represents the shape of a Nglass spectrum, while the second PC considers the height of the shoulder before ~800 nm and the dip after that point.

.

Figure 4: Clustering of spectra after PCA analyses

Future perspectives

We have observed how, for samples with identical chemical composition and different mineralogical assemblage, the spectral response within Visible and Near InfraRed (VNIR) can be substantially different. The mechanism influencing the shape of spectra results in fact from a complex interaction of the spectral response of different mineral/amorphous phases. In this way, the shape is easily misinterpreted as the features of the different phases which are often no longer recognizable. A PCA analyses helped us to understand which are the features that can be accounted for the interpretation of this kind of igneous materials, but a more comprehensive study on different compositions is needed for a complete assessment of this approach.
Acknowledgements
This work was carried on thanks to ASI-UniPG agreement 2019-2-HH.0 and in the framework of Trans-National Access research project selected and funded by Europlanet-2024 RI (European Union’s Horizon 2020 RI under grant agreement No. 871149)

How to cite: Pisello, A., Fastelli, M., Baroni, M., Schmitt, B., Beck, P., Zucchini, A., Petrelli, M., Comodi, P., and Perugini, D.: Building analogs in the lab: spectral characterization of a synthetic Nakhlite., Europlanet Science Congress 2024, Berlin, Germany, 8–13 Sep 2024, EPSC2024-1194, https://doi.org/10.5194/epsc2024-1194, 2024.

Abstract

A new set-up of open-ended coaxial line based on the capacitive-load model is developed to measure dielectric properties of materials at elevated temperatures up to 500 ^oC over the frequency range of 1 - 100 MHz. The complex reflection coefficients are measured by a Vector Network Analyzer and are translated to the complex permittivity of the material under test using transmission line theory. Measurements are conducted on a basaltic rock sample that can be considered a Venusian analog. 

INTRODUCTION

Analysis of  dielectric behavior of planetary crusts-rock analogs at planetary ambient conditions is critical to determine their impact on the propagating electromagnetic waves. A variety of measurements have been made on planetary analogs and samples at low temperatures like temperatures at Mars, Moon. However, very little is known about the dielectric properties of rocks and minerals for planetary analog materials at radar frequencies and elevated temperatures. While, for example, Envision the upcoming ESA mission (Thakur et al., 2023), aiming to study the Venus subsurface, needs measurements on some analogs at 9 MHz operating frequency and at Venusian rocks temperature that reaches to  ∼500 ^oC.

The reflection type of the transmission line method is based on the reflection of incident electromagnetic waves from the media interface that is caused by impedance discontinuity at two sides of the interface (e.g., Von Hippel, 1954; Orfanidis, 2002).

In this study, a new set-up is developed based on (Gershon et al., 1999) open-ended coaxial probe (a truncated transmission line) to measure the complex relative dielectric permittivity materials using the capacitive model.

THEORY

In a coaxial line electric fields are in the radial direction between the inner and outer conductor, and magnetic fields form circles around the inner conductor. The 1-port network analyzer measures the reflection coefficient, S₁₁, that is related to the input impedance at the probe. For a coaxial line of length d that ends with a load impedance  Z_L, the probe input impedance seen looking toward the load is expressed as (Orfanidis, 2002):

where Z_c is the characteristic impedance of the transmission line, and k is the complex propagation constant of the electromagnetic wave. For a short-circuited transmission line Z_L =∞, hence the load admittance can be obtained by:

where Z_in and Z_sh are the input impedance of the probe and short-circuited line. For differing impedances at two sides of the interface, there will be a reflection when an electromagnetic wave propagates through the interface. A commonly used technique to compute the complex permittivity of a medium is based on measuring the reflection coefficient using a network analyzer. When the open end of the coaxial line probe is connected to a sample, the capacitive model configuration of open-ended coaxial line in the reflection method can be used to characterize the dielectric properties of the material. In terms of a capacitive model, the complex relative permittivity of the sample will be

where ω is angular frequency, and C₀ is the probe capacitance. Using a reference material with the known permittivity (e.g., air with ε^r_ref = 1) the reference admittance of Y^ref_L is computed from the corresponding measured reflection coefficients.

Experimental Procedure

Figure 1 displays a schematic diagram of the probe and the probe that has been made. The reflection coefficients are measured using an Agilent E5071C Programmable Vector Network Analyzer (VNA) over the frequency range of 1-100 MHz with log frequency sweep and 1601 frequency points. Before the measurement, a preliminary calibration is performed to correct the effects of coaxial cable, connectors, adaptor, and VNA systematic errors. A  sample (a basaltic rock sample collected from Mount Etna volcano on the east coast of Sicily, Italy) is placed in an insulated Nabertherm furnace, and measurements are acquired at temperatures in the range of 100-500 ^oC with an interval of 50 ^oC. This sample can be considered as a dry Venusian analog mineral in the Venusian environment.

Figure 2  presents the spectrum of the real part of permittivity and loss tangent computed from the measured reflection coefficient at different temperatures. At room temperature, the ε′_r is almost constant, however, by increasing temperature the dispersion effects become significant. In addition, the calculated tanδ at T = 27 ^oC presents a constant value of  ∼0.02 at frequencies above 15 MHz. At lower frequencies, some instabilities appear that are related to the instrument’s limitations. 

Dielectric properties of Etna basaltic rock at temperatures from 27 ^oC to 500 ^oC and for nominal operating frequencies of ν= 9, 20, and 60 MHz with a 5 MHz bandwidth, are shown in Figure 3. The results show an increase in relative permittivity and loss tangent as frequency decreases and temperature increases. The loss tangent values are strongly influenced by temperature and are almost one order of magnitude larger at  500 ^oC than those at  27  ^oC.

Conclusion

Dielectric properties of a basaltic rock sample were determined by measuring the reflection coefficients over the temperature range 27 ^oC to 500 ^oC. An increase in the real component of relative permittivity and loss tangent was observed with temperature, which is higher at low frequencies. In addition, sample complex permittivity shows a temperature-dependent dispersion. This method can be used particularly for Venusian crust analogs. The results are critical to configuring the radar system.

References

Gershon, D. L., Calame, J., Carmel, Y., Antonsen, T., & Hutcheon, R. M. (1999). Open-ended coaxial probe for high-temperature and broad-band dielectric measurements. IEEE transactions on microwave theory and techniques, 47 (9), 1640–1648.

Orfanidis, S. J. (2002). Electromagnetic waves and antennas.

Thakur, S., Sbalchiero, E., & Bruzzone, L. (2023). Exploring Venus subsurface: Analysis of geological targets and their properties. Planetary and Space Science, 225 , 105620.

Von Hippel, A. R. (1954). Dialectics and waves. John Wiley and Sons.

How to cite: Baniamerian, J., Emanuel Lauro, S., Cosciotti, B., Brin, A., Lefevre, C., Pettinelli, E., and Mattei, E.: An experimental set-up for dielectric characterization of Venusian crust analogs at high temperatures, Europlanet Science Congress 2024, Berlin, Germany, 8–13 Sep 2024, EPSC2024-4, https://doi.org/10.5194/epsc2024-4, 2024.

The predecessor of Laplace, ICAPS, was flown in 2019 and 2023 on the Texus-56 and Texus-58 sounding rockets. The Laplace facility is planned for a usage on the ISS with a launch in 2025. Both experiments allow to investigate the very first stages of planet formation. The relevant growth processes require observation of many-particle processes consisting of millions of µm-sized particles in a low-density gas environment (typically a few 10s of Pa, such that Knudsen numbers of >>1 are achieved) for prolonged time. The latter requirement makes it necessary to perform these investigations in a microgravity environment. The ICAPS and Laplace setups allow to actively protect the dust cloud against diffusion and other external residual forces and also allow concentration of the dust cloud by means of an actively-controlled thermophoretic trap acting on all three axes.

Simultaneously, the dust cloud is made available to a number of observational instruments. As a whole, the cloud is observed in 3D from two perpendicular overview cameras while also making a small central volume of 1 mm² cross-section accessible to a dedicated long-distance microscope with high-speed imaging to facilitate non-destructive in-situ analysis of the growing dust aggregates. An extinction sensor allows to measure the light extinction throughout the cloud as a whole. Measurements of the electric charges of the individual particles can be conducted repeatedly by means of a controlled DC or AC field in order to determine charge and charge evolution.

We will present the design and techniques of the Laplace setup, the current status of the Laplace facility and demonstrate its capabilities on a few select data from the flights of ICAPS.

How to cite: von Borstel, I., Blum, J., Schräpler, R., Aktas, C., Balapanov, D., Vedernikov, A., Brisset, J., Molinski, N., and Schubert, B.: Update on the Laplace experiment as a facility to investigate the initial stage of planet formation, Europlanet Science Congress 2024, Berlin, Germany, 8–13 Sep 2024, EPSC2024-864, https://doi.org/10.5194/epsc2024-864, 2024.