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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

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.

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

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.

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

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.

Context.Particulate surfaces exhibit a surge of reflectance at low phase angles, a phenomenon referred to as the opposition effect (OE). Two mechanisms are recognized as responsible for the OE: shadow hiding (SH) and coherent backscattering. The latter is typically characterized by a small angular width of a few degrees at most and according to the theoretical prediction should exhibit wavelength and albedo dependence.Aims.We characterize the OE on the surface of Ceres using Dawn Visible InfraRed mapping spectrometer hyperspectral images at low phase angles. Furthermore, this dataset, coupled with previous observations, allows us to perform a complete spectrophotometric modeling at visual-to-infrared (VIS-IR) wavelengths (0.465–4.05μm) in the broad phase angle range ≈0°−132°.Methods.We applied Hapke’s theory to the average phase curve for Ceres. Disk-resolved properties of the OE were investigated through an empirical model.Results.Across the investigated phase angle interval, Ceres’ average phase curve exhibits a smaller back-scattering contribution for increasing wavelengths. This determines a progressive spectral reddening at larger phase angles that we hypothesize as being related to the effect of submicron roughness on the grain surface. In the OE region, the shape of the phase curves is fairly constant across the VIS range and no sharp opposition surge at very small phase angles (α< 2°) can be recognized. This would suggest a major contribution from SH to Ceres’ OE. Assuming SH as the dominant mechanism, from the OE angular width we infer a high surface porosity (≈0.9), which appears in good qualitative agreement with Ceres’ low thermal inertia. Thanks to the OE observations we derive Ceres’ VIS-IR geometric albedo with a reference value at 0.55μm of 0.098 ± 0.007. Mapping of the VIS normal albedo and OE angular width across a portion of the surface of Ceres does not reveal a spatial correlation between these quantities, consistent with SH dominating in theα= 0°−7° interval. The comparison of Ceres’V-band magnitude curve with that of other asteroids indicates that Ceres’ OE is typical of a low-albedo object and compatible with the C-class type.

Spectral parameters of Ceres measured by the Dawn/VIR imaging spectrometer are studied as a function of illumination angles, by applying a semi-empirical method based on a statistical analysis of the VIR dataset acquired up to September 2016. The study also focuses on the photometry of the Occator faculae, i.e. the brightest spots of the Ceres surface, showing an albedo up to eight times the Ceres average. The considered semi-empirical approach takes into account the small extension (and hence small dataset) of this region and lays the groundwork to apply scattering models even on such a limited area. The behavior of Ceres visible and infrared reflectance with phase angle is similar to other asteroids belonging to its same spectral class, i.e. C-type. The depth of the bands at 2.7 µm (phyllosilicates), 3.1 µm (ammonium), 3.4 µm (magnesium carbonates) and the infrared spectral slope linearly increase with phase angle, showing analogies with other asteroids and occurrence of phase reddening. The different behavior of the 3.9 µm band depth (also due to Mg carbonates), independent of illumination angles, could indicate that other carriers contribute to the 3.4 µm band and play a more important role in photometry outside the carbonate deposits. The phase function of the Occator faculae is much steeper than expected from its high albedo. Mixture of bright and dark material and larger roughness can be at the basis of this result. The phyllosilicate bands show a steeper increase with phase angle with respect to the Ceres average, due to the lower presence of dark materials, and/or again larger roughness. The absence of trends with phase angles of the two carbonate bands and of the spectral slope suggests that carbonates do not produce phase reddening.

We investigate the region of crater Haulani on Ceres with an emphasis on mineralogy as inferred from data obtained by Dawn's Visible InfraRed mapping spectrometer (VIR), combined with multispectral image products from the Dawn Framing Camera (FC) so as to enable a clear correlation with specific geologic features. Haulani, which is one of the youngest craters on Ceres, exhibits a peculiar "blue" visible to near-infrared spectral slope, and has distinct color properties as seen in multispectral composite images. In this paper, we investigate a number of spectral indices: reflectance; spectral slopes; abundance of Mg-bearing and NH4-bearing phyllosilicates; nature and abundance of carbonates, which are diagnostic of the overall crater mineralogy; plus a temperature map that highlights the major thermal anomaly found on Ceres. In addition, for the first time we quantify the abundances of several spectral endmembers by using VIR data obtained at the highest pixel resolution ( 0.1 km). The overall picture we get from all these evidences, in particular the abundance of Na- and hydrous Na-carbonates at specific locations, confirms the young age of Haulani from a mineralogical viewpoint, and suggests that the dehydration of Na-carbonates in the anhydrous form Na2CO3 may be still ongoing.