Oral presentations and abstracts
This session aims to highlight the new challenges and the missing bricks needed to understand the composition of primitive bodies through laboratory works and models.
The session focuses on the origin of inorganic and organic matter in different astrophysical environments and welcomes contributions on laboratory investigations and models of parent bodies of various meteorite groups, asteroids, comets and dwarf planets such as: a) experimental work related to the dust-regolith composition; b) observation and characterization of laboratory analogues; c) models of comet formation, and interior structure of asteroids with implications for parent body processes and evolution of small bodies in our solar system.
The session will also focus on experimental, theoretical and observational topics specifically aimed to the study organic matter in planetary bodies, including a) detection and evolution of organic compounds in the interstellar medium; b) characterization and evolution of the organic matter in the primitive bodies (meteorites, comets, IDPs); c) observation and distribution of the organic matter in the protosolar disk and planetary surfaces.
The Hayabusa2/JAXA spacecraft has orbited and studied near-Earth object Ryugu . Two sample collections have been performed and the spacecraft is currently on its way back to the Earth for an expected return in late 2020. A preliminary examination phase will follow , expected to elucidate the formation and evolution of Ryugu. Considering the limited amount of material that will be retrieved, a multi-analytical sequence is needed to maximize the scientific outcome and minimize sample loss. Among the possible laboratory techniques, IR spectroscopy is important in being totally non-destructive and comparable to remote sensing observations of small bodies . Thanks to IR imaging micro-spectroscopy, it is possible to detect and study the spatial distribution of molecular bonds associated to minerals, water and organic compounds, and their co-localization . We consider IR three dimensional (3D) micro-tomography (IR-CT) an excellent starting point in a multi-analytical sequence to be applied on returned samples . Here we report IR hyperspectral measurements of carbonaceous chondrites as a rehearsal of IR-CT and IR hyperspectral imaging that will be part of the multi-analytical sequence of the “MIN-PET CG” Hayabusa2 team (mineralogy and petrology of coarse grains) led by T. Nakamura.
We performed IR measurements in reflectance on bulk fragments of selected meteorites, and both in reflectance and transmittance on several isolated grains (sizing 20-50 µm) extracted from carbonaceous chondrites. We also analyzed individual grains of the Murchison CM meteorite prepared at Tohoku University (Japan) from three bulk samples: (1) unheated, (2) heated at 400°C, and (3) heated at 600°C . The laboratory-controlled heating was applied to simulate potential heating undergone by Ryugu surface materials, as suggested by some Hayabusa2 observations . Some of these Murchison grains were mounted on tungsten needles by means of a platinum welding performed in IEMN-Lille (France) with a focused ion beam microscope. Other grains were prepared at Tohoku University, mounted on carbon fibers using epoxy (Fig. 1).
We analyzed the samples using an IR hyperspectral imaging and micro-tomography setup installed at the SMIS beamline of the SOLEIL synchrotron (France). This setup has already been used for analyzing Hayabusa samples from asteroid Itokawa . FTIR data were collected using an Agilent Cary 670/620 microspectrometer. In transmission mode we used a X25 objective coupled with high magnification optics (providing an additional X2.5 magnification) placed in front of a 128x128 pixels FPA detector, to obtain a projected pixel size of ~0.66 µm on the focal plane, and a field of view of ~84 µm. IR-CT is performed in transmission mode using the method described by Dionnet et al. . In reflection mode we used a X15 objective, with a projected pixel size of ~5.5 µm on the focal plane, and a field of view of ~700 µm (Fig. 1). In both cases we collected hyperspectral data: for each pixel we obtained an IR spectrum in the 850-3950 cm-1 spectral range. The spatial resolution was diffractionlimited for the whole investigated spectral range.
Infrared spectra show the presence of bending and stretching absorption bands of chemical bonds (C-H, OH, Si-O, C=O, etc.) of different functional groups, as expected from literature IR spectra of Murchison and other chondrites [9,10]. The relative intensities of these bands are found to vary among different grains, and their 3D spatial distribution is heterogeneous within individual grains (see Fig. 1). Noticeable differences are found between the IR spectra of unheated and heated Murchison samples, with a general trend of increasing the anhydrous to hydrated silicate content with increasing temperature, and reducing the organic content.
Fig. 1. A typical IR reflectance hyperspectral map of an unheated Murchison sample mounted on a carbon needle (top left, microscope images in bright and dark field), with the detection of hydrated (bottom left) and anhydrous (bottom right) areas. The epoxy contribution can be clearly separated (top right).
4. Summary and Conclusions
IR data provide a first quick look at the composition, abundance and 3D distribution of mineral phases and carbonaceous materials at the scale of a few micrometers. Once regions of interest are identified by IR measurements, thin sliced sections of the samples can be analyzed by more destructive techniques to retrieve the structure and the elemental and isotopic composition of the carbonaceous component and its mineral host, down to the nanometer scale . In addition, the IR data are useful in the comparison with remote sensing observations of asteroid surfaces [7,12]. This top-down sequence will help us building a bridge between the remote sensing and in situ observations of Ryugu at macroscopic scale and the chemical and physical processes operating at the nanoscale.
The micro-spectroscopy measurements were supported by grants from Region Ile-de-France (DIM-ACAV) and SOLEIL. This work has been funded by the CNES (France) and by the ANR project CLASSY (Grant ANR-17-CE31-0004-02) of the French Agence Nationale de la Recherche. This work was partly supported by the French RENATECH network.
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How to cite: Brunetto, R., Aléon-Toppani, A., Dionnet, Z., Rubino, S., Arribard, Y., Baklouti, D., Borondics, F., Djouadi, Z., Lantz, C., Matsumoto, M., Matsuoka, M., Nakamura, T., Amano, K., Takahashi, M., Troadec, D., and Tsuchiyama, A.: Hyperspectral imaging of carbonaceous chondrites in view of the Hayabusa2 sample return, Europlanet Science Congress 2020, online, 21 Sep–9 Oct 2020, EPSC2020-121, https://doi.org/10.5194/epsc2020-121, 2020.
Introduction: Meteorites seem to come from a small number of primary parent bodies . B-, C-, Cb-, Cg-, P- and D-types, representing not less than 66% of the mass of the main belt have no analogues clearly identified in the meteorite collections . However, meteorites are not the only cosmomaterials found on Earth since no less than 30 000 tons of interplanetary dust particles (IDPs) enter the Earth’s atmosphere each year . IDPs originate from different parent bodies throughout the solar system [4, 5, 6]. The link between IDPs and asteroids can be investigated thanks to Vis-NIR spectroscopy commonly used for the classification of asteroids (0.4 - 2.5 µm). The reflectance measurements in the visible range (0.4 - 0.8 μm) performed on IDPs in the 90s  and the simulated visible near infrared (Vis-NIR) spectra of IDPs with comparison of mid infrared (Mid-IR) spectra  have shown that IDPs may be good analogues to some asteroids and in particular to the classes not sampled by meteorites. But Vis-NIR reflectance measurements of IDPs is challenging and we must understand how the measurement on an isolated micro-metric particle can be affected by physical parameters of the sample such as size, composition, and roughness.
We report here the requirements, the abilities as well as the limitations of the technique and the results obtained on 15 IDPs particles ranging 7-31 µm in size in the Vis-NIR range (0.45 - 1.0 µm).
Experiments: Our setup, installed in a clean room, consists of a Vis-NIR spectrometer (Maya2000 Pro from Ocean Optics) coupled to a macroscope (Leica Z16 APO). A Vis-NIR optical fiber (100 or 50 μm in diameter) is used to collect the light diffused by the sample which is unilaterally illuminated by a halogen source through a 1000 μm diameter fiber (phase angle of ~ 45°). By changing the magnification and/or the diameter of the collection fiber it is possible to adapt the collection spot to the grain size down to 7 μm size.
Results and discussion: To obtain a reliable reflectance spectrum of a micro-metric grain with this setup, we show that it is necessary to average spectra taken at different azimuth angles, by rotating the particle several times in the observation plane with respect to the incident light.
Based on the study of spectral slopes we found that for particles with sizes below ~ 17 µm the spectral slope increases linearly with decreasing particle sizes. This behavior is due to a bias encountered in the reflectance measurement in this size range, inducing thus a loss of the chemical information. For particle sizes larger than ∼ 17 µm the spectral slopes seem randomly distributed between ∼ -0.3 and 0.4 µm−1, and the spectra must therefore carry chemical information of the particles.
We found that the visible reflectance levels of the IDPs show a multimodal distribution. There is a lack of IDPs with reflectance level ~ 5 and ~ 8%. In addition, the majority of IDPs have rather low reflectance levels (< 10%). Some particles have reflectance levels that may be influenced by the presence of magnetite, which is sometimes found in extraterrestrial materials and could form upon atmospheric entry.
Among the studied particles we identified an IDP (L2079C18) exhibiting a feature at 0.66 µm which is similar to the one observed by remote sensing at the surface of hydrated asteroids. This is the first detection of a hydration band in the reflectance spectrum of an IDP which could indicate a possible link between hydrated IDPs with hydrated asteroid surfaces.
Acknowledgments: We are grateful to the CAPTEM NASA for providing the IDPs. This work is supported by the Programme National de Planétologie (PNP) of CNRS/INSU, co-funded by CNES. The authors also thank the ANR RAHIIA SSOM and the P2IO LabEx (ANR-10-LABX0038) in the framework Investissements d’Avenir (ANR11-IDEX-0003-01) for their supports. We thank O. Mivumbi and Y. Longval for their help and technical support for the development of the device.
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How to cite: Maupin, R., Djouadi, Z., Brunetto, R., Lantz, C., Aléon-Toppani, A., and Vernazza, P.: VIS-NIR DIFFUSE REFLECTANCE MICRO-SPECTROSCOPIC ANALYSIS OF IDPs, Europlanet Science Congress 2020, online, 21 Sep–9 Oct 2020, EPSC2020-130, https://doi.org/10.5194/epsc2020-130, 2020.
Interpretation of spectroscopic data from remote sensing strongly depends on the spectroscopic properties, particle size and temperature of materials on the observed surface. Spectral indices of silicates, carbonates, sulfates, oxides and chemicals available on public database are commonly obtained at room temperature and pressure. Whether temperature can affect spectral properties of minerals such as the peak position, band area and shape, was advanced decades ago (Singer & Roush, 1985), but a systematic laboratory study on such effects is still missing. Hitherto, few studies were performed analyzing the effects of space environment, such as low pressure and temperature, on spectroscopic features of minerals, mostly focusing on near infrared spectral region (Moroz, et al. 2000; Hinrichs & Lucey 2002; De Angelis, et al. 2019). This is especially lacking in the mid-infrared region, where laboratory data are almost completely absent. Thus, it is pivotal to acquire spectra in vacuum at various temperatures and varying the particle sizes, for better simulating space environmental conditions.
Our apparatus at INAF-Astrophysical Observatory of Arcetri allows reflectance measurements in an extended spectral range from VIS to far IR and at temperatures ranging from 64 K to 500 K. We present here a detailed analysis on temperature-dependent variation on mineral and carbonaceous chondrite samples in the spectral range 1500-400 cm-1 (6.6-25 µm in wavelength). Mineral phases and meteorites analyzed are: pyroxene, olivine, serpentine, Tagish Lake (CI2-ungruped), Aguas Zarcas (CM2) and Orgueil (CI1). Samples are prepared with particle sizes <20 μm, <200 μm, and 200-500 μm. Our results show that temperature induces spectral features modifications such as peak position shifts, band area and peak intensity changes (Fig 1). Modifications are reversible with temperature and the trend of variation is related to the sample composition and hydration level. Moreover, magnitude of temperature-dependent spectroscopic changes is strongly linked with grain size and composition, hence making this type of analysis pivotal for a correct interpretation of data collected by space telescopes and orbital spacecrafts.
Figure 1 Meteorite spectra at different temperature normalized at 1500 cm-1 in wavenumber range between 1500 cm-1 and 400 cm-1. Tagish Lake (top left panel), Orgueil (top right panel) and Aguas Zarcas (bottom left panel). All samples are sieved in grain size 200-500 µm. Spectra were acquired at different temperature step from 65 K (light blue) to 350 K (red). Position of Christiansen features (CF) and Reststrahlen bands (RB) are highlighted.
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How to cite: Poggiali, G., Brucato, J. R., Dotto, E., Ieva, S., Barucci, M. A., Pajola, M., Fornaro, T., Corazzi, M. A., Meneghin, A., and Paglialunga, D.: Temperature dependent mid-infrared (5-25 μm) reflectance spectroscopy of carbonaceous meteorites and minerals: implication for remote sensing in Solar System exploration., Europlanet Science Congress 2020, online, 21 Sep–9 Oct 2020, EPSC2020-568, https://doi.org/10.5194/epsc2020-568, 2020.
Through laboratory analyses it is possible to study the physical and chemical processes involving prebiotic molecules, the building blocks of life. Today thanks to the advent of new generation of (sub-) millimeter and centimeter interferometers (ALMA, NOEMA, ngVLA), an increasing number of interstellar complex organic molecules (iCOMs) is observed in star forming regions, pre-stellar dense cores, hot corinos, jets and outflow ardound protostars [1, 2, 3]. Hot corinos are inner compact (<100 au) and hot (>100 K) regions of some protostars . In these high-temperature regions, thermal desorption is the physical process responsible for the sublimation of frozen mantles into the gas phase and so for the presence of a rich chemistry  in the gas phase. On the other hand, iCOMs are difficult to observe in protoplanetary disks, where, for a solar-type star, the region where the temperature reaches the values for the desorption and release into the gaseous phase of water and iCOMs (water snow line) is too close to the star (≤5 au). This region is difficult to solve but a new perspective is provided by objects such as the FU Ori systems in which the young central star undergoes a sudden increase in brightness which leads to heating of the disk and quick expansion of the snow lines to large radii. This phenomenon has been observed in the protoplanetary disk around the protostar V883 Ori . Thanks to the increase in temperature of the disk and the consequent thermal desorption of the molecules, five iCOMs were recently detected: methanol, acetone, acetonitrile, acetaldehyde, and methyl formate . Moreover, outbursting young stars are good new targets for looking for organic complex molecules that thermally desorb from icy mantles. The interpretation of observations can benefit from laboratory activities, where it is possible to simulate the thermal desorption process and UV irradiation of complex molecules under simulated space conditions. Furthermore, laboratory studies on thermal desorption are fundamental to constrain parameters such as the thermal desorption temperature of a given molecule and its fragments, and the binding energies involved.
Here we reported the results that we have recently published about temperature-programmed desorption (TPD) analysis of pure formamide (HCONH2) ice and in the presence of TiO2 dust, before and after UV irradiation. We found that pure formamide desorbed at 220 K in high vacuum regime and after UV irradiation it fragmented mainly into NH2, HCO and CH2NO. These fragments are more volatile and desorbed before formamide (~180 K) at the same desorption temperature of water. The presence of water was due to residual deposition in the high vacuum chamber. It is reasonable to think, therefore, that the sublimation of water ice was responsible for releasing more volatile species. The same phenomenon probably occurs in the space where water is the most abundant molecule. Going forward with our investigation, we reproduced the condensation, irradiation, and desorption experiments with a substrate of TiO2 dust. In presence of grains, we observed evidence for a change in desorption temperature. Formamide desorption from TiO2 dust occurred at higher temperatures, that is, around 30 K above the temperature at which desorption takes place for pure formamide. A higher desorption temperature is direct evidence of the interactions described by the Van der Waals forces that were occurring between the molecule and the grains. The molecule interacts and diffuses into the grains and this is confirmed by the values of the binding energy that we found. When formamide desorbed directly from the cold finger of the cryostat (copper chromate surface), the binding energy found was (5.9 ± 0.3)·103 K; while when it desorbed from TiO2 dust, the binding energy found was (1.35 ± 0.08)·104 K, a value two times higher . Therefore, in the chemical models of sublimation, it is essential to take into account physisorption of iCOMs on grain surfaces and their diffusion to correctly describe the desorption process, that is, to constrain desorption temperatures and binding energies . Furthermore, our experiments show something more than the desorption temperature and the binding energy of formamide. The molecular fragments observed in laboratory (NH2, HCO and CH2NO) can be used to indirectly measure the presence of formamide through detection of relative abundance (e.g., [NH2]/[HCO]∼4).
We reported also preliminary results on laboratory studies about thermal desorption of ice mixtures of acetaldehyde and acetonitrile from crystalline olivine grains.
These studies offer support to observational data and improve our understanding of the role of the grain surface in enriching the chemistry in space.
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How to cite: Corazzi, M. A., Brucato, J. R., Poggiali, G., Fedele, D., and Fornaro, T.: Laboratory studies on Temperature-Programmed Desorption analyzes of prebiotic molecules in space, Europlanet Science Congress 2020, online, 21 Sep–9 Oct 2020, EPSC2020-455, https://doi.org/10.5194/epsc2020-455, 2020.
Cosmic rays, solar wind and solar energetic particles induce changes in the physical structure and chemical composition of frozen volatiles on the surface solar system outer objects, such as satellites of giant planets, centaurs and Kuiper-belt objects (e.g., Johnson 1990, Strazzulla et al. 2003, Urso et al. 2020). Such energetic particles can be responsible for the formation of C-rich refractory materials that determine the appearance of red slopes in the visible and near-infrared spectra of small bodies (e.g., Brunetto et al. 2006, Brown et al. 2011).
Laboratory experiments performed to simulate the irradiation of frozen surfaces in space show that energetic ions or electrons (keV-MeV) determine the formation of new species, not present in the original samples (e.g., Rothard et al. 2017). The subsequent warm-up of processed mixtures causes both the sublimation of volatile compounds and an increase in the molecular diffusion and reactivity. As a consequence, the chemical complexity increases and organic refractory residues are formed.
Residues are thought to be representative of the refractory materials on the surface of outer bodies as well as of cometary materials and a possible precursor of the soluble organic matter (SOM) found in meteorites (e.g., Strazzulla & Johnson 1991, Munoz-Caro & Schutte 2003, Brunetto et al. 2006, Danger et al. 2013, Baratta et al 2015, Urso et al. 2017, Poston et al. 2018}.
We present recent laboratory experiments to produce and characterize organic refractory residues produced after ion irradiation of frozen volatiles. Water, methanol and ammonia mixtures in ratios 1:1:1 and 3:1:1 are deposited at 15 K and exposed to 40 keV H+ by means of the INGMAR setup (Urso et al. 2020). After irradiation, mixtures are warmed up with a constant heating rate and organic refractory residues are formed at 300 K. Throughout the experiment, we monitor the sample evolution by means of in-situ infrared transmission spectroscopy (4000-700 cm-1, 2.5-13.3 µm).
After warmup, organic refractory residues are recovered from the irradiation chamber and are further characterized through ex-situ Very High Resolution Mass Spectrometry. The combination of both techniques allows to shed light on the composition of irradiated frozen volatiles and of residues. We also search for specific molecules by means of tandem Mass Spectrometry/High Resolution Mass Spectrometry. Furthermore, we compare the chemical composition of our samples with that of organic refractory residues produced after UV photolysis of volatile mixtures.
Our results give information on the effects induced by different experimental parameters (dose, mixture ratio) on the composition of organic refractory materials. In particular, we investigate the effects of increasing irradiation dose in the elemental abundance and in the Double Bond Equivalent (DBE) of residues. We also give the timescales necessary to observe in solar system outer objects the effects revealed in laboratory experiments, and we discuss the role of the various sources of processing (cosmic rays, solar wind, solar energetic particles) in determining changes in the chemical composition of frozen surfaces in space.
Our work supports the interpretation of space mission data and astronomical observations of comets and solar system outer objects as well as of star-forming regions in the Interstellar medium, where cosmic rays bombard icy grain mantles and thus play a role in the synthesis of complex organic molecules in the early stage of star-formation.
This work is supported by the CNES-France. INGMAR (IAS-CSNSM, Orsay) is funded by the French Programme National de Planétologie (PNP), Faculté des Sciences d'Orsay, Université Paris-Sud (Attractivité 2012), French National Research Agency ANR (contract ANR-11-BS56-0026, OGRESSE), P2IO LabEx (ANR-10-LABX-0038) in the framework Investissements d'Avenir (ANR-11-IDEX-0003-01). We thank the support from RAHIIA SSOM (ANR-16-CE29-0015). R.G.U. thanks the CNES postdoctoral program.
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How to cite: Urso, R. G., Vuitton, V., Danger, G., d'Hendecourt, L., Djouadi, Z., Flandinet, L., Mivumbi, O., Orthous-Daunay, F.-R., Ruf, A., Vinogradoff, V., Wolters, C., and Brunetto, R.: The composition of outer solar system icy surfaces: hints from the analysis of laboratory analogues, Europlanet Science Congress 2020, online, 21 Sep–9 Oct 2020, EPSC2020-135, https://doi.org/10.5194/epsc2020-135, 2020.
Planet formation in protoplanetary discs is a process whereby the primitive solids that are initially of microscopic scale, must be converted into larger objects such as pebbles (mm-cm size), planetesimals, and eventually planets. It has been acknowledged that drifting pebbles play an important role in the core accretion scenario by triggering streaming instabilities or by aiding the growth of planetary cores. Moreover, ice lines of volatile species such as water seem to be promising sites for this process. At the water ice line, the higher surface energy of ice promotes coagulation and the sublimated vapor can diffuse outward in the disk and deposit onto pebbles, allowing fast growth . These processes can then trigger streaming instabilities or core formation through gravitational collapse of small bodies. However, very little is known about the evolution of these objects’ cohesive properties and volatile content as they drift and encounter various conditions throughout the disc. Investigating the morphology, chemistry, and physical processes of pebbles close to the ice line is essential to have an insight into the overall evolution of small bodies in the early phases of protoplanetary discs. We are interested in studying the different outcomes of the sublimation of an icy pebble, to understand how its optical properties are changing over time and if the dust aggregates survive to the sublimation process. In the Laboratory for Outflow Studies of Sublimating Materials (LOSSy) at the University of Bern , we are researching optical and physical properties of ice-dust mixtures with relevance for protoplanetary discs and planet formation, with focus on the role of ice sublimation in changing these properties.
Two new methods for the preparation of ice-dust aggregate with mm-size have been developed. The first method (Pebble-A) uses an inclined superhydrophobic surface with dust on it; a mm-size droplet of distilled water rolls on it and collects the dust, then it falls into liquid nitrogen. The second method (Pebble-B) exploits the capillary forces between water and solid grains: a droplet impinges a dust bed and penetrates it forming a wet aggregate, which is then sunk in liquid nitrogen. PAs have generally ~50%wt of ice and the dust is mainly accumulated close to the surface of the pebble, while the core has more ice. PBs have lower amounts of ice (~15%wt) and the dust grains are connected through ice films. Different types of dust with relevance for protoplanetary discs are used, such as olivine, pyroxene, corundum, serpentine, CI and CR asteroids simulants . Humic acid (HA) is used as an organic compound, simulating complex organics that can be found on comets.
The SCITEAS-2 (Simulation Chamber for Imaging the Temporal Evolution of Analogue Samples version 2.0) vacuum chamber provides a low-pressure and low-temperature environment for the sublimation of icy samples, and a hyperspectral measurement of the sample over time in the VIS and NIR . The pressure inside the chamber is kept low (around 10-6 mbar) through a turbomolecular vacuum pump, and a He-cryocooler guarantees a temperature at the base of the sample of ~120 K. A fast sublimation of the icy pebbles is achieved by letting the temperature evolve freely up to room temperature, while the vacuum pump pumps out the vapor formed in the chamber. The overall process lasts around 20 hours.
Ice sublimation, gravity, grain size distribution of the dust, type of dust, ice content, and presence of organics concur all together to determine the sublimation outcome of the icy pebble. Is it going to disrupt to dust or will it maintain its shape? We list here some interesting preliminary observations:
- - ice sublimation is detectable in the VIS and NIR reflectance spectra of the pebbles. Although the disappearance of the ice absorption bands provides information on ice content at the surface of the pebble only, the core could still contain ice;
- - PAs seem to disrupt more easily with respect to PBs made of the same dust, due to the higher amount of ice that is embedded in the core, which pushes the particles away when sublimating;
- - in PAs, the presence of HA mixed with mineral powders prevents disruption, which is observed in the absence of HA (Fig.1);
- - in PBs made of pyroxene, different grain sizes result in different outcomes: PBs made of dust with grain sizes bigger than 100 microns disrupt, while smaller grain sizes are more efficient in maintaining the pebble intact, and are not affected by sublimation. Furthermore, a PB made of coarse pyroxene dust (100-300 microns) mixed with fine dust (<50 microns) can partially resist disruption, highlighting that fine dust plays a key role in cementing bigger dust particles.
A campaign of experiments is ongoing on PAs and PBs. The aim is to investigate the different physical processes that concur in the final sublimation outcome, for different dust properties. More experiments will study:
- - The grain size distribution effects on the disruption. Different minerals are expected to have different size distributions that will avoid disruption during sublimation.
- - The role of different organics in binding with mineral dust.
- - The interaction of a gas stream at low pressure with a sublimated PB or PA, to understand their shear strength and determine their stokes number.
The team from the University of Bern is supported by the Swiss National National Science Foundation and through the NCCR PlanetS.
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How to cite: Spadaccia, S., Capelo, H., Pommerol, A., and Thomas, N.: Protoplanetary discs in the laboratory: the fate of icy pebbles undergoing sublimation, Europlanet Science Congress 2020, online, 21 Sep–9 Oct 2020, EPSC2020-198, https://doi.org/10.5194/epsc2020-198, 2020.
Recent discoveries demonstrated that the surface of Mars, Ceres and other celestial bodies like asteroids and comets are characterized by the presence of ammonium bearing minerals (Dalle Ore et al., 2018; Berg et al., 2016, Poch et al., 2020). Data collected by New Horizon LORRI and Ralph emphasized the presence of ammonia on Charon, one of the Pluto’s satellites, that is, ammonium chloride, ammonium nitrate and ammonium carbonate have been claimed as the best candidates for its composition (Cook et al., 2018). Moreover, the analysis of the absorption features of Mars spectra at ~1.07, 1.31 and 1.57 μm can be related to ammonium bearing minerals (Sefton-Nash et al., 2012) as well as the presence of oceans underneath the Europa’s crust (Zimmer et al., 2000) suggests a hypothetical composition of water + ammonia, as anti-freezing water element (Sphon and Schubert, 2003). In this scenario, cryovolcanism activity (Jia et al., 2018) can give rise to an interaction between water ammonia and the surface.
This study focuses on, by taking into account sulfates, phosphates, aluminates and borates, understanding how different anionic groups and the different amount of water, affect the ammonium spectra features. Ammonium bearing minerals are of significant interest as hydrogen bonds can affect the NH4+ absorption features and the configuration of the hydrogen bonds, N-H….X, in ammonium salts (e.g. NH4Cl, NH4Br), can be quite different (Harlov et al., 2001).
All this, with a careful analysis of remote data compared with the analyses of more accurate laboratory data, should allow a better remote characterization of planetary bodies.
In this work, the reflectance spectra of some ammoniated hydrous and anhydrous salts, namely sal-ammoniac NH4Cl, larderellite NH4B5O7(OH)2·H2O, mascagnite (NH4)SO4, struvite (NH4)MgPO4·6H2O and tschermigite (NH4)Al(SO4)2·12H2O, were collected at room temperature and at 193K. These samples were selected to improve the NH4-bearing mineral reflectance spectra database and to extend the investigated spectral range with respect to the literature data: e.g. Berg et al., 2016.
We analyzed natural ammonium bearing minerals using reflectance spectroscopy in the long-wave ultraviolet (UV), visible, near-infrared (NIR), and mid-infrared (MIR) regions (~1 – 16 μm) at 298 and 198 K. In addition, thermogravimetric analysis (TG) and differential scanning calorimetry (DSC) were made to evaluate the amount of water/ammonium loss and the potential phase transitions occurring in the investigated temperature range. X-ray diffraction analyses were performed on the samples before and after thermal treatments to study the evolution of their crystal structure.
Reflectance spectra of ammoniated minerals show absorption features at 1.3, 1.6, 2.06, 2.14, 3, 3.23, 5.8 and 7.27 μm, related to ammonium group. The 2ν3 at ~1.56 μm and the ν3+ν4 at ~2.13 μm, are the most affected modes by crystal structure type, since their position is strictly related to hydrogen bonds. The reflectance spectra of water-rich samples (struvite (NH4)MgPO4·6(H2O) and tschermigite (NH4)Al(SO4)2·12(H2O)) show only fundamental absorption features in the area from 2 to 2.8 μm and a strong water feature at 3 μm. An endothermic peak at 192° C was detected in the DSC diagram of sal-ammoniac sample, due to the phase transition from CsCl structure type to NaCl type.
Important was the application of a new proprietary tool (areal mixing model RE-Mix) created to fit remote sensing data coming from planetary bodies with a mixing of the reflectance spectra of single minerals. The RE-Mix tool is based on Hapke model, the most common scattering theory used to calculate synthetic reflectance spectra (Hapke, 1981, 2012). We can assume that the surfaces of planetary bodies contain mixtures of different minerals. In the interpretation of the remote sensing data, it is therefore necessary to assume a mixture of spectra of different minerals. The spectral modelling method used inside Re-Mix is an areal mixing model, which is the most used and the least computationally intensive process. It is based on the least-squares method and the goodness of fit (χ2) is adjusted changing the weight coefficients of the single minerals. The tool is based on Wolfram Mathematica software (Wolfram 1999). A full graphical interface was developed.
The method interprets the remote sensing data from Jupiter’s moon, Europa and Ceres asteroid. We found a number of NH4-bearing mineral mixtures can fit the planetary spectra together with other mineral species, improving the hypothesis that ammonium species should be among the non-icy materials present on the surface of Galilean moons and mixed with carbonate mineral on Ceres surface.
These knowledges will give us more detailed information from the remote data and suggestions which areas and data should have higher priority for remote investigations in the future space missions.
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How to cite: Fastelli, M., Comodi, P., Piergallini, R., Maturilli, A., Balic-Zunic, T., and Zucchini, A.: Reflectance spectroscopy of ammonium-bearing minerals: a tool to improve the knowledge of the icy planetary bodies, Europlanet Science Congress 2020, online, 21 Sep–9 Oct 2020, EPSC2020-294, https://doi.org/10.5194/epsc2020-294, 2020.
Recent spectral orbital data revealed the presence of hydrated minerals on the surfaces of small bodies, mainly thanks to the identification and the study of spectral features around 3-µm [1, 2]. These features, widely detected on the spectra of carbonaceous chondrites, are indicative of the presence of (OH)-bearing minerals. However, their appearance and shape are diverse indicating different composition and/or the occurring of subsequent alteration events. It has been suggested that thermal alteration processes, can darken the surfaces of carbonaceous chondrites, thus decreasing the reflectance values around 3 µm. Thermal alteration processes, have been considered to explain the formation of 162173 Ryugu asteroid . The Near Infrared Spectrometer (NIRS3) on Hayabusa 2 mission detected a weak and narrow absorption feature centered at 2.72 µm across the entire observed surface of the C-type asteroid . However, the collected spectra from the Ryugu surface show no other absorption features in the 3-µm region. To investigate on this point and to check the behaviour of the spectral features around 3 µm with thermal alteration, we performed laboratory experiments on two Mg-rich phyllosilicates (serpentine and saponite). In particular, we studied two different situations: 1) thermal alteration at increasing T - the samples were heated at different steps of 100ᵒC, starting from 100ᵒC up to 700ᵒC, for 4 hours each; 2) long time heating at constant T - samples were heated at constant T~250ᵒC for 1 month (1st step) and then for 2 months (2nd step).
2. Experimental setup and procedure
We selected four samples of serpentine and saponite in two different grain sizes: 25-63 µm and 125-250 µm. Samples preparation, heating processes and measurements were performed in the Planetary Spectroscopy Laboratory (PSL) of the German Aerospace Center (Deutsches Zentrum für Luft- und Raumfahrt, DLR) in Berlin . Three identical FTIR (Fourier Transform Infrared Spectrometers) instruments are operated at PSL, in an air-conditioned laboratory room. The three spectrometers are all the same identical model, Bruker Vertex 80V that can be evacuated to ~.1 mbar. Two spectrometers are equipped with aluminium mirrors optimized for the UV, visible and near-IR, the third features gold-coated mirrors for the near to far IR spectral range. Using three instruments that are identical (apart from the different internal mirrors) has some major benefits. Most importantly, it facilitates the cross-calibration between the three instruments. The instruments can also share the collection of detectors, beam splitters, and optical accessories that are available in our equipment to cover a very wide spectral range.
In the first part of our experiment, samples were heated in vacuum (~ 0.1 mbar) using the induction system in the external emissivity chamber of the PSL. The temperature of the sample was increased slowly and gradually up to the desired value. T was controlled by means of temperatures sensors located inside the chamber, in contact with the sample cup (stainless steel) rim and bottom part. After reaching the targeted T, the samples were kept stable at these temperature and pressure conditions for ~ 4 hours. After each step, the heated samples were cooled down in vacuum and then measured in the whole spectral range (from UV to IR) in bidirectional reflectance. In parallel, two of the selected samples (serpentine 125-250 µm and saponite 125-250 µm) were stored in two autoclaves in an oven at 250ᵒC for 1 month (first set of samples), and then once again at the same temperature for two months (second set of samples). The 1-month and 2-months heated samples, after cooling down in the autoclaves, were measured in reflectance, with the same experimental setup used for the samples heated at different T steps. Bidirectional reflectance measurements were recorded in vacuum by using two of the Bruker Vertex80V FTIR spectrometers at PSL in two different angles configurations: 1) i=0ᵒ e=26ᵒ; 2) i=0ᵒ e=40ᵒ.
3. Results and discussion
The spectra acquired on the fresh and thermally processed samples of saponite (125-250 µm) are shown in Fig. 1.
Fig. 1. Spectra of saponite 125-250 µm in the full studied range.
Globally it is possible to observe: - a darkening effect occurring at High-T in the UV+VIS spectral range for both the analyzed samples; - a decreasing intensity with increasing T in the spectral features present in the region 0.35-0.7 µm; - general darkening has not been observed in the MIR spectral range; - a 0.95 µm (water absorption band) and a 2.3 µm (absorption usually attributed to Mg-OH stretching) features decrease with increasing T in both serpentine and saponite samples. Isolated bands and spectral parameters have been retrieved for a detailed study of the spectral features around 3-µm. We observed that: - the 2.7 µm feature is most prominent in the saponite samples and it tend to decrease with Hi-T, but without totally disappearing; - the intensity of the 2.7 µm feature features strongly decrease instead in the samples of serpentine, especially in the long heated ones; - a 3.4 µm feature is present in the spectra of high-heated serpentine from 300°C on for the 25-63 µm serpentine, and for the sample of 125-250 µm serpentine heated at 600°C and 700°C.
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How to cite: Alemanno, G., Maturilli, A., Helbert, J., and D'Amore, M.: Analysis of the 3 µm spectral features of Mg-rich phyllosilicates with temperature variations in support of the interpretation of small asteroid surface spectra, Europlanet Science Congress 2020, online, 21 Sep–9 Oct 2020, EPSC2020-560, https://doi.org/10.5194/epsc2020-560, 2020.