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Gas-surface interactions at the Moon, Mercury and other massive planetary bodies constitute, alongside production and escape, an essential element of the physics of their gravitationally bound exospheres. From condensation and accumulation of exospheric species onto the surface in response to diurnal and seasonal changes of surface temperature, to thermal accommodation, diffusion and ultimate escape of these species from the regolith back into space, surface-interactions have a drastic impact on exospheric composition, structure and dynamics. The study of this interaction at planetary bodies combines exospheric modeling and observations with a consideration of fundamental physics and laboratory experimentation in surface science. With a growing body of earth-based and spacecraft observational data, and a renewed focus on lunar missions and exploration, the connection between the exospheres and surfaces of planetary bodies is an area of active and growing research, with advances being made on problems such as topographical and epiregolith thermal effects on volatile cold trapping, among others. In this paper we review current understanding, latest developments, outstanding issues and future directions on the topic of exosphere-surface interactions at the Moon, Mercury and elsewhere.

Introduction. The ASI Space Science Data Center (SSDC) has a long-standing experience in space data management. Among its tools, MATISSE (Multi-purpose Advanced Tool for Instruments for the Solar System Exploration [1]) was created in 2013 to search, visualize and analyze data from planetary exploration missions. MATISSE, whose v2.0 update [2] is available at https://tools.ssdc.asi.it/Matisse/, allows users to analyze data from different missions, such as NASA Messenger and NASA Dawn, and the possibility of visualizing the data directly on the 3D shape of the targets greatly helped in reaching stunning scientific results. The work here presented points at improving and expanding the functionalities of the MATISSE tool for the Mercury explorations, by including the possibility to merge together the outputs of a thermophysical code of Mercury surface and the study of planet’s surface from a geological point of view. MATISSE for Mercury exploration. The ESA-JAXA BepiColombo mission is the first European mission to Mercury; the spacecraft will study in detail the surface, the exosphere and the magnetosphere of the planet. We have developed a thermophysical model with the aim to analyze the dependence of the temperature of the surface and of the layers close to it on the assumptions on the thermophysical properties of the soil. The code solves the one-dimensional heat equation, assumes purely conductive heat propagation and no internal heat sources; the surface is assumed to be composed of a regolith layer with high porosity and density increasing with depth. Calculations have been carried out to analyze the thermal response of the soil as a function of thermal conductivity. The model has been also used to study the sodium content in the planet's exosphere, whose origin is under investigation [3]; the MESSENGER mission has measured the exospheric sodium content as a function of time, detecting an increase at the "cold poles" (so called because of their lower than average temperature). In order to study the effect of surface temperatures on the sodium content in the exosphere, the temperature distribution calculated with the code has been used together with an atmospheric circulation model that calculates the exospheric sodium content [4]. Figure 1. Total sodium exospheric content as function of time and true anomaly angle, calculated in two cases: surface temperature from the thermophysical code (red line), and reference temperature (T proportional to ¼ power of cosine of illumination angle, blue line). A simplified version of the thermophysical code is available to the scientific community through MATISSE and, therefore, it could be crucial to interpret the data acquired by the instruments on board the BepiColombo mission, especially if it is taken into account that, through MATISSE, it is possible to analyze the surface of Mercury with data from NASA Messenger based on queries looking for specific geological units (as is already possible for Mars, Mercury and Ceres). Thanks to the data from the MDIS (Mercury Dual Imaging System [5]) camera on board the MESSENGER, it was possible to create a global map of the planet's surface. The identified lithologies can be analyzed and subsequently uploaded to our MATISSE tool in order to have the possibility to study the surface of Mercury directly from the site. On MATISSE it will be possible to select the data not only with the usual geographical coordinate, but on the basis of geological maps, so that the user can analyze observational and modeled data collected on areas with well-defined geology that allow to study the effects of the heterogeneity of surface. Figure 2. MATISSE homepage and selection of parameters to be observed. Example of selection of the Hokusay crater on Mercury's surface. The possibility of studying the Mercury surface directly from the tool will allow not only to make a detailed study of the terrain but understanding its formation will help science to understand how the solar wind affects some materials. For this reason our work will allow planetologists and astrophysicists to have all the available data for the study of the planet. In collaboration with the PlanMap and GMap teams, we are currently working to include the geological units identified on the surface of Mercury in order to be ready with the data that will come from the Bepi Colombo mission in order to have everything you need to study this planet in depth. Next steps. We plan to add in the tool all geological units mapped by GMAP team on Mercury surface. Moreover we will expand in the tool the possibility of searching for data based on the morphologies that the user wants to analyze (e.g. craters, valleys). Another goal will be to expand the use of the tool, making it similar to the geographic information system (GIS). We will expand the possibility of selecting specific areas to be analyzed, having clear the geographical position of the data. It will also be possible to obtain topographic profiles, select more data to be observed. All these analyses will be performed directly on the 3D models. The inclusion of these functionalities in the tool could produce a sensible step forward in the study of planetary geology, with the possibility of better exploiting different datasets and taking also into account the collaboration of different teams already leaders in this field. References. [1] Zinzi A. et al. (2016) Astron. Comput., 15, 16-28 [2] Zinzi A. et al. (2019) EPSC-DPS Joint Meeting 2019, id. EPSC-DPS2019-1272 [3] Rognini, E., et al. (2022), Effects of mercury surface temperature on the sodium abundance in its exosphere, Planetary and Space Science, 212 [4] Mura, A., et al. (2009), The sodium exosphere of Mercury: Comparison between observations during Mercury’s transit and model results, Icarus, 200, 1-11 [5] Hawkins et al., (2007). The Mercury Dual Imaging system on the MESSENGER spacecraft, Space Science Reviews, 131, 247–338

Context Circular depressions and alcoves were observed on the surface of some JFCs visited by spacecrafts: 81P/Wild 2 (Brownlee et al., 2004), 9P/Tempel 1 (Belton et al., 2013), 103P/Hartley 2 (Syal et al., 2013), and 67P/Churyumov- Gerasimenko (Vincent et al., 2015). These features are characterized by different shapes and sizes ranging from few tens to few hundreds of meters (Ip et al., 2016). Several studies investigated the thermal processing in relation to their formation and evolution (Guilbert-Lepoutre et al., 2016), and found that recent thermal activity in the inner solar system orbits is not sufficient to carve them. Ip et al. (2016) found that the size frequency distribution of the depressions on 67P, 81P and 9P has the same power law distribution, implying that they might have the same origin and formation mechanism. Dynamical simulations show that the thermal history of 81P and 9P is likely shorter than 67P’s and 103P’s, suggesting a younger surface. In this work, we investigate the thermally-induced evolution of depressions at the surface of 81P, 9P, 103P, and 67P under each of their current illumination conditions. Methods For these four nuclei, we select more than 10 surface features (i.e. depressions or alcoves). From their shape models, we select multiple facets on different sides of each feature (plateaux, bottom and walls) and consider the complete thermal environment for each facet, including self-heating and shadowing, either by neighboring facets or due to the complex global morphology of the nucleus. We compute the energy input for each facet during a full recent orbit, with a time step of ∼ 8 min. The total energy received at the surface is used as an input of a 1D thermal evolution model, which accounts for heat diffusion, phase transitions (sublimation of various ices and crystallization of amorphous water ice), gas diffusion, erosion, and dust mantling (Lasue et al., 2008). The thermal behaviour of each surface feature is investigated in detail. Results We find that self-heating can be important in deep pits and steep cliffs of 67P and 81P (~65% and ~30% of the total energy input, respectively). In comparison, it is very low for 9P and 103P’s (• Plateaux tend to erode more than the shadowed bottoms of sharp features, found on 67P and 81P: i.e. circular depressions become shallower with time. On 9P and 103P, erosion is more uniform since depressions are already shallower (as in the southern hemisphere of 67P). Overall, sharp depressions are likely erased by cometary activity.• Erosion sustained after the multiple perihelion passages is not able to carve depressions with the observed size and shape. It is therefore very unlikely that current illumination conditions were able to carve them.• We have, however, performed our simulations with a uniform set of thermo-physical parameters for all facets. Therefore, we cannot exclude that local or regional heterogeneities may yield different erosion rates.• A comparison between simulation outcomes for all nuclei allows to consider 103P as having the most altered surface. 9P could be an intermediate state. 81P would thus represent the least altered, or best preserved surface of these nuclei. Finally, 67P display a variety of surface ages, with areas as preserved as 81P, and a southern hemisphere as altered as 9P. Acknowledgements This study is part of a project that has received funding from the European Research Council (ERC) under the European Union’s Horizon 2020 research and innovation programme (Grant agreement No. 802699). We gratefully acknowledge support from the PSMN (Pôle Scientifique de Modélisation Numérique) of the ENS de Lyon for the computing resources. We thank the European Space Research and Technology Centre (ESAC) and the European Space Astronomy Centre faculty council for supporting this research. References Belton, M. J., Thomas, P., Carcich, B., et al. 2013, Icarus, 222, 477Brownlee, D. E., Horz, F., Newburn, R. L., et al. 2004, Science, 304, 1764Guilbert-Lepoutre, A., Rosenberg, E. D., Prialnik, D., & Besse, S. 2016, Monthly Notices of the Royal Astronomical Society, 462, S146Ip, W.-H., Lai, I.-L., Lee, J.-C., et al. 2016, Astronomy & Astrophysics, 591, A132Lasue, J., De Sanctis, M. C., Coradini, A., et al. 2008, Planetary and Space Science, 56, 1977Syal, M. B., Schultz, P. H., Sunshine, J. M., et al. 2013, Icarus, 222, 610Vincent, J.-B., Bodewits, D., Besse, S., et al. 2015, Nature, 523, 63

Linear features are very common on asteroid surfaces. They are generally formed after impact and provide information about asteroid evolution. This work focuses on a mineralogical and spectral analysis of the main linear features on the 1/Ceres surface, having both tectonic (Samhain Catena’s pit chains) and geomorphic origins, i.e., generated by ejecta material (Occator ejecta, Dantu’s secondary radial chains, secondary radial chains generated from the Urvara impact). The analysis is based on spectral parameters defined by the Dawn’s VIR imaging spectrometer data, as albedo and depths of the bands centered at approximately 2.7, 3.1, 3.4 and 3.9 mm. The geomorphic linear features show spectral variations with respect to the surroundings, i.e., ammoniated phyllosilicates band depth shallowing is caused by the presence of material originating in a different region or dehydration caused by impact. The Samhain Catena does not show any mineralogical variation, due to its tectonic origin. The spectral behavior of Ceres’ linear features is similar to that observed on other asteroids (Vesta, Eros) and can be diagnostic in discerning the origin of linear features. Then, we searched spectral signatures of organics in the Samhain Catena region, since they are expected to form at depth due to internal processes: the absence of such signatures indicates that either they form at a larger depth or that their subsurface distribution is uneven.

Comets evolve due to sublimation of ices embedded inside porous dust, triggering dust emission (that is, erosion) followed by mass loss, mass redistribution and surface modifications. Surface changes were revealed by the Deep Impact and Stardust NExT missions for comet 9P/Tempel 1 (ref. 1), and a full inventory of the processes modifying cometary nuclei was provided by Rosetta while it escorted comet 67P/Churyumov–Gerasimenko for approximately two years2–4. Such observations also showed puzzling water-ice-rich spots that stood out as patches optically brighter and spectrally bluer than the average cometary surface5–9. These are up to tens of metres large and indicate macroscopic compositional dishomogeneities apparently in contrast with the structural homogeneity above centimetre scales of pebble-made nuclei10. Here we show that the occurrence of blue patches determines the seasonal variability of the nucleus colour4,11,12 and gives insight into the internal structure of comets. We define a new model that links the centimetre-sized pebbles composing the nucleus10 and driving cometary activity13,14 to metre-sized water-ice-enriched blocks embedded in a drier matrix. The emergence of blue patches is due to the matrix erosion driven by CO2-ice sublimation that exposes the water-ice-enriched blocks, which in turn are eroded by water-ice sublimation when exposed to sunlight. Our model explains the observed seasonal evolution of the nucleus and reconciles the available data at micro (sub-centimetre) and macro (metre) scales.

Remote sensing data of comets 9P/Tempel 1 and 67P/Churyumov-Gerasimenko (67P hereafter) indicate the occurrence of water-ice-rich spots on the surface of cometary nuclei [1-5]. These spots are up to tens of metres in size and appear brighter and bluer than the average surface at visible wavelengths. In addition, the extensive observation campaign performed by the Visible and InfraRed Thermal Imaging Spectrometer (VIRTIS, [6]) and the Optical, Spectroscopic, and Infrared Remote Imaging System (OSIRIS, [7]) during the Rosetta escort phase at 67P revealed a seasonal cycle of the nucleus colour. This is characterised by blueing of the surface while approaching perihelion followed by progressive reddening and restoral of the original colour along the outbound orbit. The temporal evolution of the colour has been interpreted in previous studies as the result of increasing exposure of water ice at smaller heliocentric distances [8, 9], however, an explanation of such seasonal cycle in the context of a quantitative cometary activity model was not yet been provided. Recently, in [10] we showed that the seasonal colour cycle observed on comet 67P is determined by the occurrence of the above-mentioned water-ice-rich spots (referred to as Blue Patches – BPs –, given their colour). This can be explained in the context of activity models [11, 12] of pebble-made cometary nuclei [13], i.e. in terms of nucleus surface erosion induced by H2O and CO2 ices sublimation, driving the cometary activity. According to the scenario proposed in [10] (Fig. 1), the presence of the BPs is due to the exposure of subsurface sub-metre-sized Water-ice-Enriched Blocks (WEBs) thanks to surface erosion triggered by CO2 sublimation ejecting decimetre-sized chunks [12]. The WEBs are composed of ice-rich pebbles (dust-to-ice mass ratio δ=2, [14]), embedded in a matrix of drier pebbles (δ>>5) forming most of the nucleus. Once exposed to illumination as BPs, the WEBs are eroded by water-ice sublimation ejecting sub-cm dust [11]. By means of dedicated spectral and thermophysical modelling, we match the nucleus colour temporal evolution measured by the VIRTIS Mapping channel in the 0.55-0.8 µm spectral range. In doing this, we take into account the competing effects of CO2- and H2O-driven erosion that expose and remove the BPs, respectively, and are seasonally modulated by the insolation conditions, primarily depending on the heliocentric distance. The new nucleus model proposed in [10], implying an uneven distribution of water ice in cometary nuclei, reconciles the compositional dishomogeneities observed on comets (the BPs) at macroscopic (up to tens of metres) scale, with a structurally homogeneous pebble-made nucleus at small (centimetre) scale, and with the processes determining the cometary activity at microscopic (sub-pebble) scales. Figure 1. 67P surface gets bluer approaching perihelion as a consequence of the progressive exposure to sunlight of subsurface WEBs (from Figure 4 in Ciarniello et al., 2022, Nature Astronomy, https://doi.org/10.1038/s41550-022-01625-y). The comet nucleus is made of two types of pebbles, both including refractories and CO2 ice, with different water ice content: pebbles with high content of H2O ice form the WEBs, while H2O-ice-poor pebbles represent the rest of the nucleus. CO2 ice is stable beneath the CO2 sublimation front at depths >0.1 m [12]. Approaching perihelion, the CO2 ice sublimation rate increases, eroding the surface by chunk ejection and exposing the WEBs. Once exposed, WEBs lose CO2 and are observable as BPs. Water-ice sublimation erodes the BPs ejecting sub-cm dust from their surface and preventing the formation of a dry crust [11]. The BPs survive until their water-ice fraction is sublimated, producing the observed surface blueing. Please refer to ref. [10] for complete details. References [1] Sunshine, J. M. et al. (2006) Science 311, 1453–1455. [2] Filacchione, G. et al. (2016) Nature 529, 368–372. [3] Raponi, A. et al. (2016) Mon. Not. R. Astron. Soc. 462, S476-S490. [4] Barucci, M. A. et al. (2016) Astron. Astrophys. 595, A102. [5] Oklay, N. et al. (2017) Mon. Not. R. Astron. Soc. 469, S582–S597. [6] Coradini, A. et al. (2007) Space Sci. Rev. 128, 529–559. [7] Keller, H. U. et al. (2007) Space Sci. Rev. 128, 433–506. [8] Fornasier, S. et al. (2016) Science 354, 1566–1570. [9] Filacchione, G. et al. (2020) Nature 578, 49-52. [10] Ciarniello, M. et al. (2022) Nat. Astron. doi:10.1038/s41550-022-01625-y. [11] Fulle, M. et al. (2020) Mon. Not. R. Astron. Soc. 493, 4039–4044. [12] Gundlach, B. et al (2020). Mon. Not. R. Astron. Soc. 493, 3690–3715. [13] Blum, J. et al. (2017) Mon. Not. R. Astron. Soc. 469, S755–S77. [14] O’Rourke, L. et al. (2020) Nature 586, 697–701. Acknowledgements We thank the Italian Space Agency (ASI, Italy; ASI-INAF agreements I/032/05/0 and I/024/12/0), Centre National d’Etudes Spatiales (CNES, France), and Deutsches Zentrum für Luft-und Raumfahrt (DLR, Germany) for supporting this work. VIRTIS was built by a consortium from Italy, France and Germany, under the scientific responsibility of IAPS, Istituto di Astrofisica e Planetologia Spaziali of INAF, Rome, which also led the scientific operations. The VIRTIS instrument development for ESA has been funded and managed by ASI (Italy), with contributions from Observatoire de Meudon (France) financed by CNES and from DLR (Germany). The VIRTIS instrument industrial prime contractor was former Officine Galileo, now Leonardo Company, in Campi Bisenzio, Florence, Italy. Part of this research was supported by the ESA Express Procurement (EXPRO) RFP for IPL-PSS/JD/190.2016. D.K. acknowledges DFG-grant KA 3757/2-1. This work was supported by the International Space Science Institute (ISSI) through the ISSI International Team "Characterization of cometary activity of 67P/Churyumov-Gerasimenko comet". This research has made use of NASA’s Astrophysics Data System.

The Stereo Imaging Channel (STC) is one of the channels of the Spectrometer and Imagers for MPO BepiColombo Integrated Observatory SYStem (SIMBIO-SYS) onboard the ESA BepiColombo mission to Mercury. STC is a double wide-angle camera designed to image each portion of the Mercury surface from two different lines of sights, whose main aim is to provide panchromatic stereo-image pairs required to generate the Digital Terrain Model (DTM) reconstruction. In addition, selected surface areas will be acquired in color. This work presents the expected STC on-ground and in-flight performance describing the preliminary evaluation of some key parameters: the optical performance, the on-ground resolution and detector response, the achievable Signal to Noise Ratio (SNR) for different integration times and observation strategies and the global coverage of panchromatic filters during the entire scientific phase. The estimation of the SNR has been made using the STC radiometric model with Hapke reflectance model for Mercury surface and the SPICE toolkit software. The SPICE toolkit software with kernel for BepiColombo mission has been used also for the estimation of the on-ground pixel dimension and the global coverage all over the mission. (C) 2018 Elsevier Ltd. All rights reserved.

Introduction Recent high-resolution ALMA observations of protoplanetary disks have raised interest in the study of solid bodies in disks at different scales, from sub-micrometric grains up to solid bodies hundreds of meters in size, for which dynamic evolution is governed by the interaction between the gas and the dust in the disk. We propose a novel research in the field of dust evolution and dynamics in protoplanetary disks. One of the main goals of this research is to address the dust dynamics evolution, the dynamical interaction between proto-planetary bodies, preparing the path for the SKA Key Programmes. We aim at contributing to this field twofold: (i) modeling of non-spherical dust dynamics in rarefied gas field present in the disk gaps and (ii) to interpret and reconstruct protoplanetary disk observations through numerical simulations, extending the PHANTOM code [1] to non-spherical dust setup, i. e. a particular focus is how the dynamics is influenced by dust dimension and shape. One of the main objectives is to reproduce the image of ALMA data and understand how different disk initial dust parameters and dust characteristics may influence the disk evolution and face-on or edge-on appearance. Using the state-of-the-art non-spherical dust dynamical model [2], developed for analysis of the ESA comet mission ROSETTA data, we determine the region in the gaps where the settling could occur as a function of the grain non-sphericity (shape, elongation), size, density etc. We investigate the terminal velocities and rotational frequencies of the non-spherical particles using different physical particle parameters, to show that the dust accommodation in the ring structures can be at distances different than what predicted by spherical dust models. The second focus of this work is to study the vertical settling with the SPH approach taking into account the dusty-gas interaction through the whole disk including possible planet-formation gaps. Dust dynamics models We use two models to simulate dust dynamics in protoplanetary disks: 1) a non-spherical dust dynamical model to simulate dust settling in Epstein regime and 2) the-state-of-the-art SPH code PHANTOM to simulate dust motion in both the Epstein and Stokes regimes. The first code is a 3D+t non-spherical dust model that solves the Euler dynamical and kinetic equations. Considering free-collisional dust regime we study the effects on the particle dynamics provided with different particle shapes, initial orientation and velocities, as well as torque. Torque is computed from the law of variation of the angular momentum by using the Euler dynamic equations. The particles are assumed to be homogeneous, isothermal convex bodies. The dust motion is governed by the gas drag and gravity of the host star and/or a planet in the gaps. The second model is a modified version of the PHANTOM code. We introduced non-spherical ellipsoidal particles and averaged drag coefficients for those non-spherical shapes. The code is a 3D+t SPH and MHD code and includes modules for self-gravity, dust-gas mixtures, viscosity, photo-evaporation, etc. A description of the parameters set used in these simulations with the results of simulations of dust settling are reported in Fig. 2. The plot is an example of dust settling in dusty disks, each of them having only one of three selected types of particles that are of the same mass and density, but of different shape. Dust settling with non-spherical particles Here we discuss two example cases produced by the two codes. Fig.1 shows rotational frequency (number of rotation per second) of two spheroids of different aspect ratio calculated with our non-spherical dust model in the Epstein regime. We simulate the dynamical properties and evolution of μm to mm sized particles in the case study with a planet in a disk gap at 60 AU, as observed in the HD163296 data [3, 4]. We assess the structure of the hypothesized vertically-extended dust layer. We investigated the influence of different dust sizes and initial dust speeds. Different spheroids of the same mass lead to different dynamics (e.g. velocity, angular velocity, etc) in the vertical settling phenomena. In the second group of simulations our non-spherical dust setup of the PHANTOM code has been used. By utilizing the pre-calculated averaged drag coefficients of spheroid particles in Epstein regime we simulated dust vertical settling in a disk using the SPH approach. The non-spherical dust particles in Epstein regime settle down slower than their spherical equivalent particles (see Fig 2). Moreover, the settling of larger non-spherical dust particles in Stokes regime shows a stratified structure: a denser sub-disk near the mid-plane for dust in Stokes regime and suspended particles in Epstein regime. Conclusions and future work We used two different models to simulate non-spherical dust settling in protoplanetary disks. The first one computes dusty-gas motion in Epstein regime using free molecular expression for rarefied field [1]. The second one uses a newly implemented feature of the state-of-the-art PHANTOM code, namely non-spherical dust shapes. Both models reveal that the interpretation of the ALMA observations can be biased by the spherical particle approximation. In our future work we will describe what we found applying the two dust models with non-spherical particles to study the dust evolution of edge-on disks. Usually the mm-sized particles settling in protoplanetary disks are aggregates of fractals formed from the dusty-gas interactions during the protostellar nebula phase. Such aggregates could be approximated with compact porous particles if dynamical (e.g. drag coefficients) and physical (e.g. porosity, density, fractal dimension) parameters are taken into account. Acknowledgments This research was supported by the National Institute for Astrophysics, Italy (INAF) within the Mainstream project “Non-spherical dust dynamics in protoplanetary disks - how realistic dust particle shapes change the dust evolution timescales”. References [1] Price D. J. et al. (2018), PASA 35, E031 [2] Ivanovski S. et al. (2017), Icarus 282, p. 333 - 350. [3] Isella et al. 2016, PRL, 117; [4] ALMA Partnership et al. 2015, ApJ Lett. 808:L3,10pp

The characterization of the surface material of airless bodies is important for the comprehension of the geology and evolution, and also for mission decisions as the selection of the sample site. The thermophysical properties affect the surface temperature curve, that is the temperature as function of time; the thermal inertia, defined by TI=(k ρ c)0.5 (where k is the thermal conductivity, ρ the density and c the specific heat), is the key parameter that controls the maximum daytime temperature and the time at wich the maximum occurs. A thermophysical model requires to properly model the thermal conductivity of the soil; common thermophysical models assume that surface material (regolith or rock) can be approximated as a continuous, non-discretized material whose physical properties are constant or vary with depth in some mathematical way, e.g. the density increases exponentially with depth. These assumptions are valid when the particles sizes are smaller than the thermal skin depth; however, high-resolution images of the Nightingale Crater on Bennu (DellaGiustina et al., 2019) revealed a particle size distribution in which the particles are smaller/larger than, and comparable to, the diurnal skin depth (that is of order of cm). Furthermore, the Bennu's moderate thermal inertia appears to be inconsistent with the large number of boulders, suggesting that the link between thermal inertia and particle size is not adeguately captured by standard models. We have included in our thermophysical model (Rognini et al., 2019; Capria et al., 2014) the effects of the particle size distribution, using the results of Ryan et al. (2020); numerical simulations by these authors indicate that the thermal conductivity of a polydisperse soil is approximated by the thermal conductivity of a monodisperse soil with a particle diameter equal to Sauter mean D32, that is the diameter of a particle with the same volume-to-area ratio. Corrections for non-isothermality of the particles are also included. These modifications allow us to properly model the temperature of rubble pile asteroids and analyze the thermal data from future missions; in particular, we want to apply our model to Ryugu and Bennu, the goals of JAXA and NASA missions Hayabusa 2 and Osiris-Rex, respectively, although the model can be used for the general case. We investigate how to use the simulation results of our thermophysical model as input for the non-spherical dust dynamics model (Ivanovski et al., 2017) that has been modified to study dust motion in near asteroid environments after recent and future impacts on rubble-pile asteroids performed by JAXA and NASA missions. Furthermore, we plan to constrain the dust distribution based on the data and simulations obtained by these missions. This will allow to foresee what kind of dust environment the ESA mission HERA could find at the encounter with the Didymos binary system. A version of the thermophysical code is almost ready to be available to the scientific community through MATISSE, the webtool developed at the SSDC in ASI (Zinzi et al., 2016); the modifications reported in this work will be included. Figure 1: examples of temperature curves calculated with different average particle sizes D=D32 (meters), for a point located on the equator of an asteroid with emissivity 0.9, heliocentric distance 1.6 A.U., albedo 0.1, density 2146 kg/m3, specific heat 600 J kg-1 K-1, rotation period 11.92 h. References: Capria, M. T., Tosi, F., De Sanctis, C., et al. (2014), Vesta surface thermal properties map, AGU, DOI:10.1002/2013GL059026 DellaGiustina, D.N., Emery, J.P., et al. (2019), Properties of rubble-pile asteroid (101955) Bennu from OSIRIS-REx imaging and thermal analysis, Nature Astronomy, DOI:10.1038/s41550-019-0731-1 Ivanovski, S. L., Zakharov, V. V., et al. (2017), Dynamics of aspherical dust grains in a cometary atmosphere: I. axially symmetric grains in a spherically symmetric atmosphere, Icarus, DOI:10.1016/j.icarus.2016.09.024 Rognini, E., Capria, M. T., Tosi, F., De Sanctis, C., et al. (2019), High Thermal Inertia Zones on Ceres From Dawn Data, JGR, DOI:10.1029/2018JE005733 Ryan, A., Pino Muñoz, D., Bernacki, M., Delbo, M. (2020), Full-Field Modeling of Heat Transfer in Asteroid Regolith: Radiative Thermal Conductivity of Polydisperse Particulates, JGR:Planets. DOI:10.1029/2019JE006100 Zinzi, A., et al. (2016), MATISSE: A novel tool to access, visualize and analyse data from planetary exploration missions, Astronomy and Computing, DOI:10.1016/j.ascom.2016.02.006

We present an investigation of the emission intensity of CO2and H2O and their distribution in the coma of 67P/ Churyumov–Gerasimenko obtained by the VIRTIS-M imaging spectrometer on the Rosetta mission. We analyze 4 data cubes from Feb. 28, and 7 data cubes from April 27, 2015. For both data sets the spacecraft was at a sufficiently large distance from the comet to allow images of the whole nucleus and the surrounding coma. We find that unlike water which has a reasonably predictable behavior and correlates well with the solar illumination, CO2outgasses mostly in local regions or spots. Furthermore for the data on April 27, the CO2evolves almost exclusively from the southern hemisphere, a region of the comet that has not received solar illumination since the comet's last perihelion passage. Because CO2and H2O have such disparate origins, deriving mixing ratios from local column density measurements cannot provide a meaningful measurement of the CO2/H2O ratio in the coma of the comet. We obtain total production rates of H2O and CO2by integrating the band intensity in an annulus surrounding the nucleus and obtain pro-forma production rate CO2/H2O mixing ratios of ∼5.0% and ∼2.5% for Feb. 28 and April 27, respectively. Because of the highly variable nature of the CO2evolution from the surface we do not believe that these numbers are diagnostic of the comet's bulk CO2/H2O composition. We believe that our investigation provides an explanation for the large observed variations reported in the literature for the CO2/H2O production rate ratios. Our mixing ratio maps indicate that, besides the difference in vapor pressure of the two gases, this ratio depends on the comet's rotational orientation combined with its complex geometric shape which can result in quite variable rates of erosion for different surface areas such as the northern and southern hemisphere. Our annulus measurement for the total water production for Feb. 28 at 2.21AU from the Sun is 2.5×1026molecules/s while for April 27 at 1.76 AU it is 4.65×1026. We find that about 83% of the H2O resides in the illuminated portion of our annulus and about 17% on the night side. We also make an attempt to obtain the fraction of the H2O production coming from the highly active neck of the comet versus the rest of the illuminated surface from the pole-on view of Feb. 28 and estimate that about 60% of the H2O derives from the neck area. A rough estimate of the water surface evaporation rate of the illuminated nucleus for April 27 yields about 5×1019molecules/s/m2. Spatial radial profiles of H2O on April 27 on the illuminated side of the comet, extending from 1.78 to 6.47km from the nucleus center, show that water follows model predictions quite well, with the gas accelerating as it expands into the coma. Our dayside radial profile allows us to make an empirical determination of the expansion velocity of water. On the night side the spatial profile of water follows 1/ρ. The CO2profiles do not exhibit any acceleration into the coma but are closely matched by a 1/ρprofile.

Dust is the most abundant component in cometary comae. Here, we investigate the dust size distribution in 67P/Churyumov-Gerasimenko (67P/CG) using data from the Rosetta spacecraft that was in close proximity to the comet from 2014 August to 2016 September. The Visual, Infrared and Thermal Imaging Spectrometer (VIRTIS-M), spectral range of 0.25–5 μm, and the Grain Impact Analyser and Dust Accumulator (GIADA), both part of the Rosetta payload, together provide a powerful means to characterize the dust coma properties. On March 28, Rosetta performed a flyby close to the nucleus that allowed GIADA to detect a large amount of dust particles used to constraint the differential size distribution power-law index of −2.2 ± 0.3. In April 2015, VIRTIS-M observed the spectral radiance in the wavelength range of 1–5 μm. A simple radiative transfer model has been applied to simulate the VIRTIS-M radiances, thus allowing to infer the dust properties. We assumed an optically thin dust coma and spherical amorphous carbon particles in the size range between 0.1 to 1000 μm. We obtained the infrared data best fit with a differential dust size distribution power-law index of −3.1 . This index matches the one determined using GIADA March 2015 data indicating that, before perihelion, the inner coma radiance is dominated by particles larger than 10 μm; and the dust coma did not change its properties during most of the 67P/CG inbound orbit. + 3 − 0.1

The HYPerspectral Stereo Observing System (HYPSOS) is a novel remote sensing pushbroom instrument able to give simultaneously both 3D spatial and spectral information of the observed features. HYPSOS is a very compact instrument, which makes it attractive for both possible planetary observation and for its use on a nanosat, e.g. for civilian applications. This instrument collects light from two different perspectives, as a classical pushbroom stereocamera, which allows to realize the tridimensional model of the observed surface, and then to extract the spectral information from each resolved element, thus obtaining a full 4-dimensional hypercube dataset. To demonstrate the actual performance of this novel type of instrument, we are presently realizing a HYPSOS prototype, that is an instrument breadboard to be tested in a laboratory environment. For checking its performance, we setup an optical facility representative of a possible flight configuration. In this paper we provide a description of HYPSOS concept, of its optomechanical design and of the ground support equipment used to characterize the instrument. An update on the present status of the experiment is finally given.

The BepiColombo mission is the first European mission to Mercury; the spacecraft will reach its destination in December 2025, and will study in detail the surface, the exosphere and the magnetosphere of the planet. We have developed a thermophysical model with the aim to analyze the dependence of the temperature of the surface and of the layers close to it on the assumptions on the thermophysical properties of the soil. The code solves the one-dimensional heat equation, assumes purely conductive heat propagation and no internal heat sources; the surface is assumed to be composed of a regolith layer with high porosity and density increasing with depth. The illumination conditions are calculated by using a Mercury shape model and the SPICE routines [1]. The model will help us to interpret the data that will be provided by the instruments onboard the BepiColombo mission. Preliminary calculations have been carried out to analyze the thermal response of the soil as a function of thermal conductivity. The model is currently also used to study the sodium content in the planet's exosphere, whose origin is under investigation [2]; the MESSENGER mission has measured the exospheric sodium content as a function of time, detecting an increase at the "cold poles" (so called because of their lower than average temperature). We therefore want to study the effect of surface temperatures on the sodium content in the exosphere; for this purpose, the temperature distribution calculated with the code is used together with an atmospheric circulation model that calculates the exospheric sodium content [3]. A simplified version of the thermophysical code is almost ready to be available to the scientific community through MATISSE [4], the software developed at the SSDC in ASI and available at https://tools.ssdc.asi.it/Matisse. [1] Acton, C. H. (1996), Planetary and Space Science, 44, 65-70[2] Cassidy, T., et al. (2016), GRL, 43, 11 121-128[3] Mura, A., et al. (2009), Icarus, 1, 1-11[4] Zinzi, A., et al. (2016), Astronomy & Computing, 15, 16-28

Exocomets are small bodies releasing gas and dust which orbit stars other than the Sun. Their existence was first inferred from the detection of variable absorption features in stellar spectra in the late 1980s using spectroscopy. More recently, they have been detected through photometric transits from space, and through far-IR/mm gas emission within debris disks. As (exo)comets are considered to contain the most pristine material accessible in stellar systems, they hold the potential to give us information about early stage formation and evolution conditions of extra Solar Systems. In the Solar System, comets carry the physical and chemical memory of the protoplanetary disk environment where they formed, providing relevant information on processes in the primordial solar nebula. The aim of this paper is to compare essential compositional properties between Solar System comets and exocomets. The paper aims to highlight commonalities and to discuss differences which may aid the communication between the involved research communities and perhaps also avoid misconceptions. Exocomets likely vary in their composition depending on their formation environment like Solar System comets do, and since exocomets are not resolved spatially, they pose a challenge when comparing them to high fidelity observations of Solar System comets. Observations of gas around main sequence stars, spectroscopic observations of "polluted" white dwarf atmospheres and spectroscopic observations of transiting exocomets suggest that exocomets may show compositional similarities with Solar System comets. The recent interstellar visitor 2I/Borisov showed gas, dust and nuclear properties similar to that of Solar System comets. This raises the tantalising prospect that observations of interstellar comets may help bridge the fields of exocomet and Solar System comets., Comment: 25 pages, 3 figures. To be published in PASP. This paper is the product of a workshop at the Lorentz Centre in Leiden, the Netherlands

The latest developments of planetary exploration missions devoted to minor bodies required new solutions to correctly visualize and analyze data acquired over irregularly shaped bodies. ASI Space Science Data Center (SSDC - ASI, formerly ASDC - ASI Science Data Center) worked on this task since early 2013, when started developing the web tool MATISSE (Multi-purpose Advanced Tool for the Instruments of the Solar System Exploration) mainly focused on the Rosetta/ESA space mission data. In order to visualize very high-resolution shape models, MATISSE uses a Python module (vtpMaker), which can also be launched as a stand-alone command-line software. MATISSE and vtpMaker are part of the SSDC contribution to the new challenges imposed by the "orbital exploration" of minor bodies: (1) MATISSE allows to search for specific observations inside datasets and then analyze them in parallel, providing high-level outputs; (2) the 3D capabilities of both tools are critical in inferring information otherwise difficult to retrieve for non-spherical targets and, as in the case for the GIADA instrument onboard Rosetta, to visualize data related to the coma. New tasks and features adding valuable capabilities to the minor bodies SSDC tools are planned for the near future thanks to new collaborations.

Comets are usually considered to be the most primitive bodies in the Solar System. The level of truth of this paradigm, however, is a matter of debate, especially if by primitive we mean that they represent a sample of intact, unprocessed material. We now have the possibility of analysing the comet 67P/Churyumov-Gerasimenko with an unprecedented level of detail, but its interior remains largely unprobed and unknown. The questions we address in this paper concern the depth of the processed layers, and whether the comet nucleus, under these processed layers, is really representative of the original material. We applied the Rome model for the thermal evolution and differentiation of nuclei to give an estimation of the evolution and depth of the active layers and of the interplay between the erosion process and the penetration of the heat wave. In order to characterize the illumination regime and the activity on the nucleus, two locations with very different illumination histories were chosen for the simulation. For both locations, the bulk of the activity tends to be concentrated around the perihelion time, giving rise to a high erosion rate. As a consequence, the active layers tend to remain close to the surface, and the interior of the comet, below a layer of few tens of centimetres, can be considered as pristine.

Context.Cometary outgassing is induced by the sublimation of ices and the ejection of dust originating from the nucleus. Therefore measuring the composition and dynamics of the cometary gas provides information concerning the interior composition of the body. Nevertheless, the bulk composition differs from the coma composition, and numerical models are required to simulate the main physical processes induced by the illumination of the icy body.Aims.The objectives of this study are to bring new constraints on the interior composition of the nucleus of comet 67P/Churyumov-Gerasimenko (hereafter 67P) by comparing the results of a thermophysical model applied to the nucleus of 67P and the coma measurements made by the Reflectron-type Time-Of-Flight (RTOF) mass spectrometer. This last is one of the three instruments of the Rosetta Orbiter Spectrometer for Ion and Neutral Analysis (ROSINA), used during the Rosetta mission.Methods.Using a thermophysical model of the comet nucleus, we studied the evolution of the stratigraphy (position of the sublimation and crystallisation fronts), the temperature of the surface and subsurface, and the dynamics and spatial distribution of the volatiles (H2O, CO2and CO). We compared them with the in situ measurements from ROSINA/RTOF and an inverse coma model.Results.We observed the evolution of the surface and near surface temperature, and the deepening of sublimation fronts. The thickness of the dust layer covering the surface strongly influences the H2O outgassing but not the more volatiles species. The CO outgassing is highly sensitive to the initial CO/H2O ratio, as well as to the presence of trapped CO in the amorphous ice.Conclusions.The study of the influence of the initial parameters on the computed volatile fluxes and the comparison with ROSINA/RTOF measurements provide a range of values for an initial dust mantle thickness and a range of values for the volatile ratio. These imply the presence of trapped CO. Nevertheless, further studies are required to reproduce the strong change of behaviour observed in RTOF measurements between September 2014 and February 2015.

Thermal inertia is a key information to quantify the physical status of a planetary surface. We derive the thermal inertia of the surface of Ceres using spatially resolved data from the Dawn mission. For each location, this quantity can be constrained by comparing theoretical and observed diurnal temperature profiles from retrieved temperatures. We calculated Ceres's surface theoretical temperatures with a thermophysical model that provides temperature as a function of thermal conductivity and roughness, and we determined the values of those parameters for which the best fit with the observed data is obtained. Our results suggest that the area of crater Haulani displays thermal inertia values (up to 130-140 J·m-2·s-½·K-1) substantially higher than the very low to low values (from 1-15 to 50-60 J·m-2·s-½·K-1) derived for the overall surface of Ceres. The results are more ambiguous for the bright faculae located in the floor of crater Occator.

On 30 August 2019 the amateur Borisov discovered a new comet; after few days it was clear from the characteristics of its orbit (eccentricity > 3 and high hyperbolic excess velocity) that the second interstellar object had been detected and the object received the name of 2I/Borisov. It appears to be very different from 1I/’Oumuamua and can be considered as the first interstellar comet. According to the first observations the comet had a nucleus with a radius of few km and a dust coma and tail due to the activity started in June 2019 (Jewitt et al., 2019). At the beginning of October we submitted the Discretionary Director Time (DDT) proposal to the TNG in order to monitor the comet. Some images have been acquired, in November and December 2019, with the DOLORES instrument in the R filter. We have applied the dust model described in Fulle et al. (2010), that has been tested on the comet 67P/Churyumov-Gerasimenko and validated with the Rosetta measurements. According to the results of our dust model and the activity model (Fulle et al., 2020) we derived a water flux from the nucleus of 8x10-6 kg m-2 s-1 and a dust loss rate of 35 and 30 kg s-1 in November and December 2019 respectively (Cremonese et al., 2020). This slight decrease has been observed around the perihelion on 8 December, few months later the comet fragmented. In this work we will describe the dust tail observations and the dust model results, even comparing them with the Jupiter family comet 67P. References: G.Cremonese, et al., 2020, ApJL, 893, L12 M.Fulle et al., 2010, A&A, 522, A63. M.Fulle et al., 2020, MNRAS, 493, 4039. Jewitt et al., 2019, ApJ, 886, L29.

The Europlanet H2020 program started on 1/9/2015 for 4 years. It includes an activity to adapt Virtual Observatory (VO) techniques to Planetary Science data called VESPA. The objective is to facilitate searches in big archives as well as sparse databases, to provide simple data access and on-line visualization, and to allow small data providers to make their data available in an interoperable environment with minimum effort The VESPA system, based on a prototype developed in a previous program [1], has been hugely improved during the first two years of Europlanet H2020: the infrastructure has been upgraded to describe data in many fields more accurately; the main user search interface (http://vespa.obspm.fr) has been redesigned to provide more flexibility; alternative ways to access Planetary Science data services from VO tools have been implemented; VO tools are being improved to handle specificities of Solar System data, e.g. measurements in reflected light, coordinate systems, etc. Current steps include the development of a connection between the VO world and GIS tools, and integration of Heliophysics, planetary plasmas, and mineral spectroscopy data to support of the analysis of observations.Existing data services have been updated, and new ones have been designed. The global objective is already overstepped, with 34 services open and 20 more being finalized.A procedure to install data services has been documented, and hands-on sessions are organized twice a year at EGU and EPSC; this is intended to favour the installation of services by individual research teams, e.g. to distribute derived data related to a published study. In complement, regular discussions are held with big data providers, starting with space agencies (IPDA). Common projects with ESA and NASA’s PDS have been engaged, with the goal to connect PDS4 and EPN-TAP. In parallel, a Solar System Interest Group has just been started in IVOA; the goal is here to adapt existing astronomy standards to Planetary Science.

Open Access article, published by EDP Sciences, under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/4.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. Open Access funding provided by Max Planck Society., On 27 April 2015, when comet 67P/Churyumov-Gerasimenko was at 1.76 au from the Sun and moving toward perihelion, the OSIRIS and VIRTIS-M instruments on board the Rosetta spacecraft simultaneously observed the evolving dust and gas coma during a complete rotation of the comet.© C. Tubiana et al. 2019, OSIRIS was built by a consortium led by the Max-Planck-Institut fur Sonnensystemforschung, Gottingen, Germany, in collaboration with CISAS, University of Padova, Italy, the Laboratoire d'Astrophysique de Marseille, France, the Instituto de Astrofisica de Andalucia, CSIC, Granada, Spain, the Scientific Support Office of the European Space Agency, Noordwijk, The Netherlands, the Instituto Nacional de Tecnica Aeroespacial, Madrid, Spain, the Universidad Politechnica de Madrid, Spain, the Department of Physics and Astronomy of Uppsala University, Sweden, and the Institut fur Daten-technik und Kommunikationsnetze der Technischen Universitat Braunschweig, Germany. The support of the national funding agencies of Germany (DLR), France (CNES), Italy (ASI), Spain (MEC), Sweden (SNSB), and the ESA Technical Directorate is gratefully acknowledged. We thank the Rosetta Science Ground Segment at ESAC, the Rosetta Mission Operations Centre at ESOC and the Rosetta Project at ESTEC for their outstanding work enabling the science return of the Rosetta Mission. VIRTIS was built by a consortium, which includes Italy, France, and Germany, under the scientific responsibility of the Istituto di Astrofisica e Planetologia Spaziali of INAF, Italy, which also guides the scientific operations. The VIRTIS instrument development, led by the prime contractor Leonardo-Finmeccanica (Florence, Italy), has been funded and managed by ASI, with contributions from Observatoire de Meudon financed by CNES, and from DLR. We thank the Rosetta Science Ground Segment and the Rosetta Mission Operations Centre for their support throughout all the phases of the mission. The VIRTIS calibrated data will be available through the ESA's Planetary Science Archive Website (www.rssd.esa.int) and is available upon request until posted to the archive. We thank the following institutions and agencies for support of this work: Italian Space Agency (ASI, Italy) contract number I/024/12/1, Centre National d'Etudes Spatiales (CNES, France), DLR (Germany), NASA (USA) Rosetta Program, and Science and Technology Facilities Council (UK).

The SIMBIO-SYS simulator is a useful tool to test the instrument performance and to predict the instrument behaviour during the whole scientific mission. It has been developed with Interactive Data Language (IDL), and it give three groups of output data: i) the geometrical quantities related to the spacecraft and the channels, which include both the general information about the spacecraft and the information for each filter; ii) the radiometric outputs, which include the planet reflectance, the radiance and the expected signal measured by the detector; iii) the quantities related to the channel performance, which are for example the integration time (IT), which has to be defined to avoid the detector saturation, the expected dark current of the detector.

The ESA-JAXA mission BepiColombo toward Mercury will be launched in October 2018. On board of the European module, MPO (Mercury Planetary Orbiter), the remote sensing suite SIMBIOSYS will cover the imaging demand of the mission. The suite consists of three channels dedicated to imaging and spectroscopy in the spectral range between 420 nm and 2 ?m. STC (STereo Imaging Channel) will provide the global three-dimensional reconstruction of the Mercury surface with a vertical accuracy better than 80 m and, as a secondary scientific objective, it will operate in target oriented mode for the acquisition of multi spectral images with a spatial scale of 65 m along-track at the periherm for the first orbit at Mercury. STC consists in 2 sub-channels looking at the Mercury surface with an angle of ±20° with respect to the nadir direction. Most of the optical elements and the detector are shared by the two STC sub-channels and to satisfy the scientific objectives six filters strips are mounted directly in front of the sensor. An off-axis and unobstructed optical configuration has been chosen to enhance the imaging contrast capabilities of the instrument and to allow to reduce the impact of the ghosts and stray light. The scope of this work is to present the on-ground geometric calibration pipeline adopted for the STC instrument. For instruments dedicated to 3D reconstruction, a careful geometric calibration is important, since distortion removal has a direct impact on the registration and the mosaicking of the images. The definition of the distortion for off-axis optical configuration is not trivial, this fact forced the development of a distortion map model based on the RFM (rational function model). In contrast to other existing models, which are based on linear estimates, the RFM is not specialized to any particular lens geometry, and is sufficiently general to model different distortion types, as it will be demonstrated.

International audience; The Europlanet H2020 program started on 1/9/2015 for 4 years. It includes an activity to adapt Virtual Observatory (VO) techniques to Planetary Science data called VESPA. The objective is to facilitate searches in big archives as well as sparse databases, to provide simple data access and on-line visualization, and to allow small data providers to make their data available in an interoperable environment with minimum effort The VESPA system, based on a prototype developed in a previous program [1], has been hugely improved during the first two years of Europlanet H2020: the infrastructure has been upgraded to describe data in many fields more accurately; the main user search interface (http://vespa.obspm.fr) has been redesigned to provide more flexibility; alternative ways to access Planetary Science data services from VO tools have been implemented; VO tools are being improved to handle specificities of Solar System data, e.g. measurements in reflected light, coordinate systems, etc. Current steps include the development of a connection between the VO world and GIS tools, and integration of Heliophysics, planetary plasmas, and mineral spectroscopy data to support of the analysis of observations.Existing data services have been updated, and new ones have been designed. The global objective is already overstepped, with 34 services open and 20 more being finalized.A procedure to install data services has been documented, and hands-on sessions are organized twice a year at EGU and EPSC; this is intended to favour the installation of services by individual research teams, e.g. to distribute derived data related to a published study. In complement, regular discussions are held with big data providers, starting with space agencies (IPDA). Common projects with ESA and NASA’s PDS have been engaged, with the goal to connect PDS4 and EPN-TAP. In parallel, a Solar System Interest Group has just been started in IVOA; the goal is here to adapt existing astronomy standards to Planetary Science.

The Stereo Imaging Channel (STC) is a double wide angle camera designed to image each portion of the Mercury surface from two different perspectives, providing panchromatic stereo-image pairs required for the Digital Terrain Model (DTM) reconstruction. In addition, selected surface areas will be acquired in color. STC is one of the channels of Spectrometer and Imagers for MPO BepiColombo-Integrated Observatory SYStem. In this work we evaluate the STC Signal to Noise Ratio (SNR) for different observation strategies and for the different phases of the BepiColombo mission. The estimation of the SNR is obtained using the radiometric model developed for SIMBIO-SYS, which takes into account the Hapke reflectance model for Mercury surface.

Local detection of increasing amount of water ice on Ceres’ surface indicates an active body and a possible seasonal cycle., The dwarf planet Ceres is known to host a considerable amount of water in its interior, and areas of water ice were detected by the Dawn spacecraft on its surface. Moreover, sporadic water and hydroxyl emissions have been observed from space telescopes. We report the detection of water ice in a mid-latitude crater and its unexpected variation with time. The Dawn spectrometer data show a change of water ice signatures over a period of 6 months, which is well modeled as ~2-km2 increase of water ice. The observed increase, coupled with Ceres’ orbital parameters, points to an ongoing process that seems correlated with solar flux. The reported variation on Ceres’ surface indicates that this body is chemically and physically active at the present time.

Hydrated carbonates indicate that the surface of Ceres is recent and dehydration is ongoing, implying a still-evolving body., Different carbonates have been detected on Ceres, and their abundance and spatial distribution have been mapped using a visible and infrared mapping spectrometer (VIR), the Dawn imaging spectrometer. Carbonates are abundant and ubiquitous across the surface, but variations in the strength and position of infrared spectral absorptions indicate variations in the composition and amount of these minerals. Mg-Ca carbonates are detected all over the surface, but localized areas show Na carbonates, such as natrite (Na2CO3) and hydrated Na carbonates (for example, Na2CO3·H2O). Their geological settings and accessory NH4-bearing phases suggest the upwelling, excavation, and exposure of salts formed from Na-CO3-NH4-Cl brine solutions at multiple locations across the planet. The presence of the hydrated carbonates indicates that their formation/exposure on Ceres’ surface is geologically recent and dehydration to the anhydrous form (Na2CO3) is ongoing, implying a still-evolving body.

The European AstRoMap project (supported by the European Commission Seventh Framework Programme) surveyed the state of the art of astrobiology in Europe and beyond and produced the first European roadmap for astrobiology research. In the context of this roadmap, astrobiology is understood as the study of the origin, evolution, and distribution of life in the context of cosmic evolution; this includes habitability in the Solar System and beyond. The AstRoMap Roadmap identifies five research topics, specifies several key scientific objectives for each topic, and suggests ways to achieve all the objectives. The five AstRoMap Research Topics are • Research Topic 1: Origin and Evolution of Planetary Systems• Research Topic 2: Origins of Organic Compounds in Space• Research Topic 3: Rock-Water-Carbon Interactions, Organic Synthesis on Earth, and Steps to Life• Research Topic 4: Life and Habitability• Research Topic 5: Biosignatures as Facilitating Life Detection It is strongly recommended that steps be taken towards the definition and implementation of a European Astrobiology Platform (or Institute) to streamline and optimize the scientific return by using a coordinated infrastructure and funding system. Key Words: Astrobiology roadmap—Europe—Origin and evolution of life—Habitability—Life detection—Life in extreme environments. Astrobiology 16, 201–243., Table of Contents 1. Introduction 1.1. The project AstRoMap within the Framework Programme for Research and Innovation (FP7) of the European Union 1.2. The European astrobiology environment and landscape in Europe 1.3. Setting the scene: timeline and astrobiology concepts 2. The Astrobiology Roadmap for Europe 3. Research Topic 1: Origin and Evolution of Planetary Systems 3.1. State of the art 3.2. Key objectives 3.3. Approach to achieve the key objectives 3.4. European strengths and needs 4. Research Topic 2: Origins of Organic Compounds in Space 4.1. State of the art 4.2. Key objectives 4.3. Approach to achieve the key objectives 4.4. European strengths and needs 5. Research Topic 3: Rock-Water-Carbon Interactions, Organic Synthesis on Earth, and Steps to Life 5.1. State of the art 5.2. Key objectives 5.3. Approach to achieve the key objectives 5.4. European strengths and needs 6. Research Topic 4: Life and Habitability 6.1. State of the art 6.2. Key objectives 6.3. Approach to achieve the key objectives 6.4. European strengths and needs 7. Research Topic 5: Biosignatures as Facilitating Life Detection 7.1. State of the art 7.2. Key objectives 7.3. Approach to achieve the key objectives 7.4. European strengths and needs 8. Conclusions and Recommendations 8.1. Cross-cutting issues of relevance 8.2. Towards a better coordination of astrobiology research in Europe—the need for a pan-European platform Acknowledgments References Abbreviations Used

The discovery of olivine on Vesta’s surface by the VIR imaging spectrometer onboard the Dawn space mission has forced us to reconsider our views of Vestan petrogenetic models. Olivines were expected to be present in the interior of Vesta: in the mantle of a vertically layered body as invoked by the magma ocean models, or at the base (or within) the mantle–crust boundary as proposed by fractionation models. Olivines have been detected by VIR-Dawn in two wide areas near Arruntia and Bellicia, regions located in the northern hemisphere. Interestingly, these olivine-rich terrains are far from the Rheasilvia and the more ancient Veneneia basins, which are expected to have excavated the crust down to reach the mantle. In this work we present our attempts to identify other undetected olivine rich areas on Vesta by using spectral parameters sensitive to olivine such as the Band Area Ratio (BAR) and other specific parameters created for the detection of olivines on Mars (forsterite, fayalite and a generic olivine index). As a preliminary step we calibrated these parameters by means of VIS–IR spectra of different HED meteorite samples: behaviors versus sample grain size and albedo were analyzed and discussed. We selected the BAR and the Forsterite Index as the best parameters that can be used on Vesta. A cross-correlation analysis has been applied in order to detect olivine signature on the VIR hyperspectral cubes. These detections have then been confirmed by an anti-correlation analysis between the BAR and one of the olivine parameters, independent of the first method applied. In agreement with the recent discovery, Arruntia and Bellicia were found to be as the most olivine-rich areas, i.e. where the parameter values are strongest. In addition we detected 6 new regions, all but one located in the Vesta north hemisphere. This result confirms again that the old petrogenetic models cannot be straightforwardly applied to Vesta and should be reshaped in the view of these new detections. An alternative and very recent option can be represented by the model according to which surface “eruption” of material from the mantle, including olivine can reach the surface of Vesta.

BepiColombo is the first ambitious, multi-spacecraft mission of ESA/JAXA to Mercury. It will be launched in October 2018 from Kourou, French Guiana, starting a 7-year journey, which will bring its modules to the innermost planet of the solar system. The Stereo Camera (STC) is part of the SIMBIO-SYS instrument, the Italian suite for imaging in visible and near infrared which is mounted on the BepiColombo European module, i.e. the Mercury Planetary Orbiter (MPO). STC represents the first push-frame stereo camera on board of an ESA satellite and its main objective is the global three-dimensional reconstruction of the Mercury surface. The harsh environment around Mercury and the new stereo acquisition concept adopted for STC pushed our team to conceive a new design for the camera and to carry out specific calibration activities to validate its photogrammetric performance. Two divergent optical channels converging the collected light onto a unique optical head, consisting in an off-axis telescope, will provide images of the surface with an on-ground resolution at periherm of 58 m and a vertical precision of 80 m. The observation strategies and operation procedures have been designed to optimize the data-volume and guarantee the global mapping considering the MPO orbit. Multiple calibrations have been performed on-ground and they will be repeated during the mission to improve the instrument performance: the dark side of the planet will be exploited for dark calibrations while stellar fields will be acquired to perform geometrical and radiometric calibrations.

The magmatism characterizing the early history of the asteroid Vesta has long been investigated with the mafic and ultramafic meteorites howardite, eucrite, and diogenite (HED). The lack of geologic context for the meteorites, however, has limited its understanding. Here we use the visible to near-IR (VIR) orbital observations of Vesta's surface to detect relative enrichments in olivine and to study the associated geologic features. Because the near-IR signature of olivine on Vesta's surface is subtle relative to the widespread pyroxene absorption bands, a method was developed to distinguish olivine enrichments from admixture of pyroxenes with high Fe2+/M1, dark material, and potential Fe-bearing glass. Relative enrichment of olivine (~

The first ever regional thermal properties map of Vesta has been derived from the temperatures retrieved by infrared data by the mission Dawn. The low average value of thermal inertia, 30 ± 10 J m−2 s−0.5 K−1, indicates a surface covered by a fine regolith. A range of thermal inertia values suggesting terrains with different physical properties has been determined. The lower thermal inertia of the regions north of the equator suggests that they are covered by an older, more processed surface. A few specific areas have higher than average thermal inertia values, indicative of a more compact material. The highest thermal inertia value has been determined on the Marcia crater, known for its pitted terrain and the presence of hydroxyl in the ejecta. Our results suggest that this type of terrain can be the result of soil compaction following the degassing of a local subsurface reservoir of volatiles.

The STereo imaging Channel (STC) is the first push-frame stereo camera on board an European Space Agency (ESA) satellite, i.e., the ESA-Japan Aerospace eXploration Agency mission BepiColombo. It was launched in October 2018, and it will reach its target, Mercury, in 2025. The STC main aim is to provide the global three-dimensional reconstruction of the Mercury surface. STC, the stereo channel of spectrometer and imagers for Mercury Planetary Orbiter BepiColombo-Integrated Observatory System, is based on an original optical design that incorporates the advantages of a compact unique detector instrument and the convenience of a double direction acquisition system. In fact, STC operates in a push-frame imaging mode and its two optical sub-channels will converge the incoming light on a single focal plane assembly allowing to minimize mass and volume. The focal plane of the instrument is housing six different filters: two panchromatic filters in the range 600-800 nm and four broadband filters with central wavelengths in the range 420-920 nm. In this paper, the geometrical calibration of the instrument, including the optical setups used, will be described. The methods used to derive the focal lengths, the boresights, and the reference systems of the different filter models are presented, and the related distortion results are discussed. The STC off-axis configuration forced to develop a distortion map model based on the RFM (rational function model). In contrast to other existing models, which allow linear estimates, the RFM is not referred to specific lens geometry, but it is sufficiently general to model a variety of distortion types, as it will be demonstrated in this particular case. Published under license by AIP Publishing.

Although olivine was expected to occur within the deep, south-pole basins of asteroid Vesta, which are thought to be excavated mantle rocks, spectral data from NASA’s Dawn spacecraft show that it instead occurs as near-surface materials in Vesta’s northern hemisphere. Between July 2011 and September 2012, NASA's Dawn spacecraft was in orbit around the asteroid Vesta. In this paper, Dawn's Visible and Infrared Mapping Spectrometer (VIR) team presents a surprising finding — the signature of olivine on the asteroid's surface. Olivine is a major component of the mantle of differentiated bodies, including Earth. Vesta is a large asteroid, large enough to have differentiated into an Earth-like layered structure and the expectation was that olivine would be found within Vesta's deep, south-pole basins, thought to be excavated mantle rocks. Yet the spectroscopic data reveal olivine-rich material close to the surface in the northern hemisphere. An understanding of the differentiation processes that have occurred on Vesta will be invaluable as a window on the primordial Solar System, but these latest findings show that Vesta's evolutionary history is more complicated than was thought. Olivine is a major component of the mantle of differentiated bodies, including Earth. Howardite, eucrite and diogenite (HED) meteorites represent regolith, basaltic-crust, lower-crust and possibly ultramafic-mantle samples of asteroid Vesta, which is the lone surviving, large, differentiated, basaltic rocky protoplanet in the Solar System1. Only a few of these meteorites, the orthopyroxene-rich diogenites, contain olivine, typically with a concentration of less than 25 per cent by volume2. Olivine was tentatively identified on Vesta3,4, on the basis of spectral and colour data, but other observations did not confirm its presence5. Here we report that olivine is indeed present locally on Vesta’s surface but that, unexpectedly, it has not been found within the deep, south-pole basins, which are thought to be excavated mantle rocks6,7,8. Instead, it occurs as near-surface materials in the northern hemisphere. Unlike the meteorites, the olivine-rich (more than 50 per cent by volume) material is not associated with diogenite but seems to be mixed with howardite, the most common7,9 surface material. Olivine is exposed in crater walls and in ejecta scattered diffusely over a broad area. The size of the olivine exposures and the absence of associated diogenite favour a mantle source, but the exposures are located far from the deep impact basins. The amount and distribution of observed olivine-rich material suggest a complex evolutionary history for Vesta.

Organic compounds detected on CeresWater and organic molecules were delivered to the early Earth by the impacts of comets and asteroids. De Sanctiset al.examined infrared spectra taken by the Dawn spacecraft as it orbited Ceres, the largest object in the asteroid belt (see the Perspective by Küppers). In some small patches on the surface, they detected absorption bands characteristic of aliphatic organic compounds. The authors ruled out an external origin, such as an impact, suggesting that the material must have formed on Ceres. Together with other compounds detected previously, this supports the existence of a complex prebiotic chemistry at some point in Ceres' history.Science, this issue p.719; see also p.692

From August to November 2014 the Rosetta orbiter has performed an extensive observation campaign aimed at the characterization of 67P/CG nucleus properties and to the selection of the Philae landing site. The campaign led to the production of a global map of the illuminated portion of 67P/CG nucleus. During this prelanding phase the comet's heliocentric distance decreased from 3.62 to 2.93 AU while Rosetta was orbiting around the nucleus at distances between 100 to 10 km. VIRTIS-M, the Visible and InfraRed Thermal Imaging Spectrometer - Mapping channel (Coradini et al. 2007) onboard the orbiter, has acquired 0.25-5.1 micron hyperspectral data of the entire illuminated surface, e.g. the north hemisphere and the equatorial regions, with spatial resolution between 2.5 and 25 m/pixel. I/F spectra have been corrected for thermal emission removal in the 3.5-5.1 micron range and for surface's photometric response. The resulting reflectance spectra have been used to compute several Cometary Spectral Indicators (CSI): single scattering albedo at 0.55 micron, 0.5-0.8 micron and 1.0-2.5 micron spectral slopes, 3.2 micron organic material and 2.0 micron water ice band parameters (center, depth) with the aim to map their spatial distribution on the surface and to study their temporal variability as the nucleus moved towards the Sun. Indeed, throughout the investigated period, the nucleus surface shows a significant increase of the single scattering albedo along with a decrease of the 0.5-0.8 and 1.0-2.5 micron spectral slopes, indicating a flattening of the reflectance. We attribute the origin of this effect to the partial removal of the dust layer caused by the increased contribution of water sublimation to the gaseous activity as comet crossed the frost-line., 19 Figures, 5 Tables. Accepted for publication in Icarus journal on 29 February 2016

The European Space Agency’s Rosetta spacecraft is the first Solar System mission to include instrumentation capable of measuring planetary thermal fluxes at both near-IR (VIRTIS) and submillimeter–millimeter (smm–mm, MIRO) wavelengths. Its primary mission is a 1 year reconnaissance of Comet 67P/Churyumov–Gerasimenko beginning in 2014. During a 2010 close fly-by of Asteroid 21 Lutetia, the VIRTIS and MIRO instruments provided complementary data that have been analyzed to produce a consistent model of Lutetia’s surface layer thermal and electrical properties, including a physical model of self-heating. VIRTIS dayside measurements provided highly resolved 1 K accuracy surface temperatures that required a low thermal inertia, I 2 s 0.5 ). MIRO smm and mm measurements of polar night thermal fluxes produced constraints on Lutetia’s subsurface thermal properties to depths comparable to the seasonal thermal wave, yielding a model of I 2 s 0.5 ) in the upper few centimeters, increasing with depth in a manner very similar to that of Earth’s Moon. Subsequent MIRO-based model predictions of the dayside surface temperatures reveal negative offsets of ∼5–30 K from the higher VIRTIS-measurements. By adding surface roughness in the form of 50% fractional coverage of hemispherical mini-craters to the MIRO-based thermal model, sufficient self-heating is produced to largely remove the offsets relative to the VIRTIS measurements and also reproduce the thermal limb brightening features (relative to a smooth surface model) seen by VIRTIS. The Lutetia physical property constraints provided by the VIRTIS and MIRO data sets demonstrate the unique diagnostic capabilities of combined infrared and submillimeter/millimeter thermal flux measurements.

We present new reflectance spectra of 12 V-type asteroids obtained at the 3.6 m Telescopio Nazionale Galileo (TNG) covering the spectral range 0.7 to 2.5 μm. This spectral range, encompassing the 1 and 2 μm, pyroxene features, allows a precise mineralogical characterization of the asteroids. The spectra of these asteroids are examined and compared to spectra for the Howardite, Eucrite and Diogenite (HED) meteorites, of which Vesta is believed to be the parent body. The observed objects were selected from different dynamical populations with the aim to verify if there exist spectral parameters that can shed light on the origin of the objects. A reassessment of data previously published has also been performed using a new methodology. We derive spectral parameters from NIR spectra to infer mineralogical information of the observed asteroids. The V-type asteroids here discussed show mainly orthopyroxene mineralogy although some of them seem to have a mineralogical composition containing cations that are smaller than Mg cations. Most of the observed Vestoids show a low abundance of Ca (

The Dawn spectrometer (VIR) is a hyperspectral spectrometer with imaging capability. The design fully accomplishes Dawn’s scientific and measurement objectives. Determination of the mineral composition of surface materials in their geologic context is a primary Dawn objective. The nature of the solid compounds of the asteroid (silicates, oxides, salts, organics and ices) can be identified by visual and infrared spectroscopy using high spatial resolution imaging to map the heterogeneity of asteroid surfaces and high spectral resolution spectroscopy to determine the composition unambiguously. The VIR Spectrometer—covering the range from the near UV (0.25 μm) to the near IR (5.0 μm) and having moderate to high spectral resolution and imaging capabilities—is the appropriate instrument for the determination of the asteroid global and local properties. VIR combines two data channels in one compact instrument. The visible channel covers 0.25–1.05 μm and the infrared channel covers 1–5.0 μm. VIR is inherited from the VIRTIS mapping spectrometer (Coradini et al. in Planet. Space Sci. 46:1291–1304, 1998; Reininger et al. in Proc. SPIE 2819:66–77, 1996) on board the ESA Rosetta mission. It will be operated for more than 2 years and spend more than 10 years in space.

Rotational properties can strongly influence a comet's evolution in terms of activity, dust mantling, and internal structure. In this paper, we investigate the effects of various rotation axis directions on the activity, internal structure, and dust mantling of cometary nuclei. The numerical code developed is able to reproduce different shapes and spin axis inclinations, taking into account both the latitudinal and the longitudinal variations of illumination, using a quasi-three-dimensional approach. The results obtained show that local variations in the dust and gas fluxes can be induced by the different spin axis directions and completely different behaviors of the comet evolution can result in the same cometary shape by using different obliquities of the models. The internal structures of cometary nuclei are also influenced by comet obliquity, as well as dust mantling. Gas and dust production rates show diversities related to the comet seasons.

著者人数：156名, Accepted: 2008-05-27, 資料番号: SA1000998000

The typically dark surface of the dwarf planet Ceres is punctuated by areas of much higher albedo, most prominently in the Occator crater. These small bright areas have been tentatively interpreted as containing a large amount of hydrated magnesium sulfate, in contrast to the average surface, which is a mixture of low-albedo materials and magnesium phyllosilicates, ammoniated phyllosilicates and carbonates. Here we report high spatial and spectral resolution near-infrared observations of the bright areas in the Occator crater on Ceres. Spectra of these bright areas are consistent with a large amount of sodium carbonate, constituting the most concentrated known extraterrestrial occurrence of carbonate on kilometre-wide scales in the Solar System. The carbonates are mixed with a dark component and small amounts of phyllosilicates, as well as ammonium carbonate or ammonium chloride. Some of these compounds have also been detected in the plume of Saturn’s sixth-largest moon Enceladus. The compounds are endogenous and we propose that they are the solid residue of crystallization of brines and entrained altered solids that reached the surface from below. The heat source may have been transient (triggered by impact heating). Alternatively, internal temperatures may be above the eutectic temperature of subsurface brines, in which case fluids may exist at depth on Ceres today.