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Numerical simulations are required to thermophysically characterize Oxia Planum, the landing site of the mission ExoMars 2022. A drilling system is installed on the ExoMars rover, and it will be able to analyze down to 2 meters in the subsurface of Mars. The spectrometer Ma_MISS (Mars Multispectral Imager for Subsurface, Coradini and Da Pieve, 2001) will investigate the lateral wall of the borehole generated by the drill, providing hyperspectral images. It is not fully clear if water ice can be found in the subsurface at Oxia Planum. However, Ma_MISS has the capability to characterize and map the presence of possible ices, in particular water ice. We performed simulations of the subsurface temperatures by varying the thermal inertia, and we quantified the effects of self-heating. Moreover, we quantified the heat released by the drilling operations, by exploring different frictional coefficients and angular drill velocities, in order to evaluate the lifetime of possible water ice.

Introduction. Oxia Planum is the selected landing site of the ExoMars mission [1]. A drilling system is installed on the ExoMars rover, able to analyze down two meters in the subsurface of Mars. Among the scientific objectives of the ExoMars mission, the searching of the organics or volatiles species plays an important role. The Ma_Miss spectrometer (Mars Multispectral Imager for Subsurface) [2] will investigate the borehole generated by the drill and it will be able to characterize and map the presence of possible ices. In this work we developed a numerical model to predict the subsurface temperatures after the heat released by the drilling operations. The increase in temperature due to the drilling operations, in fact, could affect the survivor of the volatile species [3]. Here we report the results about subsurface temperature of Oxia Planum. Numerical modeling We developed a numerical modeling to predict the subsurface temperature of Oxia Planum. In the subsurface we solve the classical heat equation [3]: where ρ is the density, c p the specific heat, K the thermal conductivity and T the temperature. Heat transfer occurs only by conduction since convection is negligible due to the small temperature gradients involved as well as the characteristic size of the sample. At the top we imposed a radiation boundary condition. In order to take into account the heat released by the drilling operations we imposed a frictional heating flux on the sides “in contact” with the drill (the lateral sides of the borehole of Fig.1). This flux is defined by the equation [3]: where η is the coefficient of friction, Fn the thrust, ω the rotational velocity, r the radius of the hole and h the height of the domain of integration (in our case 50 cm). The parameters adopted in this work are F n = 300 N, rpm = 30 or 60, η = 0.3 or 0.9, tip density = 3500 kg m-3, tip thermal conductivity = 540 W m-1K-1, tip specific heat = 790 J kg-1K-1 and a drilling window of 90 min, characterized by 30 min in “on mode”, followed by 30 min in "off mode” and finally 30 min in “on mode”. The surface and subsurface of Oxia Planum is characterized by a thermal inertia of 650 TIU, with an initial temperature fixed to 200 K. Some assumptions are made: I) instantaneous drilling(drill excavation is not modeled); 2) constant thrust; 3) constant rotational velocity. Fig.1: Geometry adopted in this work. The borehole of the drilling system is represented by the cylinder embedded in this domain of integration, with a radius of 13 mm (the thickness of the drill tip). In Fig.2 we report an example of 1-D temperature profile at z=50 cm (the maximum depth of the borehole). In the x-axis we report the distance from the hole, where shadowed red rectangle identifies the drill (or equivalently the borehole). Top panel of Fig.2 is characterized by rpm=30 and η=0.3 while the bottom panel by rpm=30 and η = 0.9. From these plots we note a difference, in the maximum value after 90 minutes, of about 40 K in favour of the case with η=0.9. The increase in temperature due to the drilling operations, in case of η=0.9, respect the initial assumed value (200 K) is about 80 K. The initial value of 200 K is chosen since is close to the surface equilibrium temperature value for Mars. As in [4] we can calculate the lifetime of an ice spherical deposit of mass m0, with a radius equal to the radius of the drill tip. The relative loss of ice mass at time (t) after the deposit is raised the temperature T is: where t is the time expressed in seconds. In this equation, Г represent the water rate emission, rp the radius of the tip and рice the density of the ice. By using the maximum sublimation rate, we obtain in case of rpm = 30 and η=0.3 a loss of about 60% of the initial mass, while in case η=0.9 of the loss is complete. In Fig.2 we report an example of temperature internal profile after the heat released by the drilling operations. Both panels refer to rpm=30: top panel is characterized by η=0.3 while bottom panel by η=0.9. Summary and Conclusions. We simulated the heat released by the drilling operations in different case of friction (η) and rotatonal speed (rpm) of the drill. We observed that in case of η=0.3 the maximum temperature increase at a depth of 50 cm is about 55 K (with rpm=30) and about 75 K (with rpm=60), while in case of η=0.9, the maximum temperature increase becomes 90 K (with rpm=30) and 130 K (with rpm=60) [3]. We also calculated the sublimation rate and the lifetime of a hypothetical spherical ice-rich deposit, with a radius equal to the size of the tip of the drill. We obtained that, after 90 minutes from the start of our simulations, in the coldest scenario (η=0.3 and rpm=30) the remaining initial mass is about the 60%, while in the other scenarios we have a complete loss of the mass [3]. Future improvements in the numerical model (e.g. a complete treatment of the diffusion of volatiles) as well as validation with laboratory experiments will be made. Acknowledgments. This work is funded and supported by the Italian Space Agency (ASI) [Grant ASI-INAF n. 2017-48-H.0].References [1] Vago J.L. et al. 2017; [2] De Sanctis M.C. et al 2017; [3] Formisano M. et al. 2021; [4] Andreas E.L. 2007; [5] Coradini A. et al. 2001

Introduction We developed a simple model to simulate Ma_MISS data acquisition and visualization and to support the development of acquisition strategies. The Ma_MISS instrument Ma_MISS (Mars Multispectral Imager for Subsurface Studies) is the miniaturized VNIR spectrometer embedded in the drill system of the ExoMars rover[1]. Ma_MISS will perform spectral reflectance measurements inside holes drilled into the surface of Mars up to a depth of 2 m. It will characterize the mineralogy and stratigraphy of the borehole walls and will allow the in-situ study of the subsurface environment, before any samples are collected and extracted. Taking advantage of the finely controllable drill tool motion, Ma_MISS can map the borehole walls. In addition to single point acquisitions, Ma_MISS can also be programmed to acquire “Ring” and “Column” scans, where the spectrometric acquisitions are interleaved with step rotations or translations of the drill tool. Borehole stratigraphy model To easily simulate Ma_MISS surveys, we first developed a simple model of a borehole. As further described in [2], six different simulant samples were prepared. Reflectance spectra were acquired on each of the samples with DAVIS-MOT, the new Ma_MISS laboratory model[3]. The reflectance spectra of these samples are shown in Figure 1. Six different regions were drawn as polylines on a 2D projection of the cylindrical borehole walls. Out of the six simulants, a different one was assigned to each region. As shown in Figure 2, this model was made to represents a 250 mm deep section of a borehole, exhibiting a varied stratigraphy with 5 different layers and a vertical vein. Figure 1: Reflectance spectra of samples. Figure 2: Borehole stratigraphy model Survey simulation The borehole model can be used to quickly simulate a Ma_MISS survey. Once the acquisition strategy of the survey is defined, the coordinates of the points where spectrometric acquisitions are to be simulated are computed. Small random errors can be added to the coordinates to simulate the accuracy of the drill tool actuators and sensors. For each point of this set, we generate a spectrum that simulates the real acquisition. Each simulated spectrum is generated from the measured spectra of one of the six simulants, based on its region in the stratigraphy model, with the addition of random shifts, slopes, and noise to simulate out-of-focus acquisitions and instrumental noise. Development of acquisition strategies The simulated data can be used to develop acquisition strategies, aimed at maximizing the information gained while limiting the time required to complete a survey of a drilled borehole. The time required to complete the survey depends on both the spectrometer acquisition settings and the drill tool motion. For example, the duration of a drill movement depends on angular and vertical step sizes (hereafter referred to as Δθ and Δz respectively), with vertical translations generally taking longer than rotations. Multiple combination of these parameters can be tried out on the same stratigraphy model to evaluate which strategy can provide the best compromise between spatial resolution and time required. Simulated data examplesFor the 4th RSOWG (Rover Science Operations Working Group) Simulation, held in November 2021, we provided data from a simulated Ma_MISS acquisition survey. The simulated Ma_MISS survey (“survey A”) consisted of: -6 rings of 360 points each, with Δθ=1° and displaced vertically by Δz=50mm; -8 columns made up of 126 points each, taken with Δθ=45° and a vertical step of Δz=2mm.This amounts to a total of 3168 individual spectra. A view of the simulated data is shown in Figure 3 and Figure 5A. This acquisition strategy provides a high angular resolution in the rings with Δθ=1° (which can be useful to identify small vertical features or individual grains) and a good vertical resolution in the column with Δz=2mm (useful to reconstruct the stratigraphy of the subsurface). Another survey (“survey B”) that was simulated with the same model is shown in Figure 4 and Figure 5B-C. In this case the acquisition was made up of 35 rings of 72 points each, with Δθ=5° and Δz=6.25 mm, for a total of 2952 spectra. This strategy offers worse spatial resolution in both the vertical direction and along the circumference but can nonetheless provide a more regular overall view of the borehole stratigraphy. Figure 3: Simulated survey A Figure 4: Simulated survey B Data visualization In Figure 3 and 4, each dot represents a simulated spectrum. In this case the colour of each dot was computed from its spectrum such that it looks somewhat like it would appear to the human eye. The same colours were interpolated across the surface (with a scattered data bicubic interpolation method) to obtain views like those shown in Figure 5A-B. Other useful visualizations of these spectra can be obtained by highlighting other spectral features, e.g., band depths, band ratios or specific IR bands. An example is shown in Figure 5C, where the 1.95 µm band depth is computed on the simulated spectra of survey B and its value is interpolated across the cylindrical surface. Figure 5: Visualization of simulated data on the borehole surface Future work The developed simulation model can be easily extended to other borehole stratigraphy models, with different geometries and spectra. It will also be complemented with tools to estimate the time needed to perform each simulated survey, which will make it a useful tool for the optimization of acquisition strategies. The developed data visualization tools can also be used with real, measured data. We are planning to verify the simulated data on real surveys. In fact, we can perform a complete survey with the Ma_MISS laboratory breadboard on an actual drilled sample. The acquired data will be visualized and used to reconstruct the sample stratigraphy. Acknowledgments This work is supported by the Italian Space Agency (ASI) grant ASI-INAF n. 2017-412-H.0. References[1] De Sanctis M.C. et al. (2017): Astrobiology, 17, 6-7[2] Ferrari M. et al. (2022): LPSC53, Abstract#1339[3] De Angelis S. et al. (2022): LPSC53, Abstract#1796

Introduction: ExoMars rover Rosalind Franklin will search for traces of past or present life potentially preserved in the designated landing site Oxia Planum [1]. Oxia is located in the western part of Arabia Terra, where geology shows evidence of a past long-lived liquid water body [2]. This clay-bearing plain is overlapped by deltaic system material provided by channels of Coogoon Valles. Spectral detections underlie the possible presence of Fe-rich phyllosilicate (for example vermiculite) and Mg-rich phyllosilicate (for example saponite) mixed with a variable amount of olivine. A mafic coating-resistant unit seems to be present [3,4,5]. Many minerals are expected to be analyzed by the Ma_MISS (Mars Multispectral Imager for Subsurface Studies) instrument at the landing site. The drill is also made up of three extensible 50 cm-long rods. The instrument is a VNIR (0.4–2.3 µm) miniaturized spectrometer in-stalled into the rover drill’s tip. It will acquire borehole spectral images in situ to study the subsurface mineralogy up to 2 m depth with a spatial resolution of 120 µm for looking at organics traces. Ma_MISS is composed of the Optical Head with fibres into the tip and the other fibres in the rods, while the spectrometer and the electronic are outside on the drill box. The sapphire window in the main rod allows the 5W light to illuminate inside the borehole and the reflected signal to be acquired by the spectrometer. The light illuminates a 1 mm diameter spot at ~0.6 mm focal distance. Thanks to drill rotation and vertical movement, Ma_MISS can collect several points to reconstruct a complete borehole image [1]. Laboratory breadboard: Drill for Analogues and Visible-Infrared Spectrometer (DAVIS) is the recent laboratory setup consisting of Laboratory Drill (DAVIS-LD) and Ma_MISS Optical Tool (DAVIS-MOT) (Figure 1). The first one (LD) is the replica of the rover drill except for the spectral acquisition system. The vertical motion is actuated by a hand lever to drill a hole in the rock samples. The motor unit is the same as the flight model but the controller is a commercial EC motor, which control the rotational speed (50 rpm) [6]. The second one (MOT) comprises a 75 cm-long and 25.4 mm-diameter rod, 5W lamp, Sapphire window, Optical Head, and an optical fibre. It is the copy of rover Ma_MISS except for the drilling ability. In this case, rover spectrometer is replaced with two Avantes VIS-NIR spectrometers. The Optical Head fibre is connected with the Avantes fibre through a mini-Avim connector. Being a replica of Ma_MISS, the light spot has 1 mm diameter at ~0.6 mm focal distance and the spatial resolution is 120 µm. It acquire in two different configurations: 1) Slab or powder samples are hosted in a vertical three-axis sample-holder and 2) manual motion of the rod to enter in the sample borehole [7]. Figure 1 – a) Ma_MISS Optical Tool (DAVIS-MOT) and b) Laboratory Drill (DAVIS-LD). Martian Analogue sample: The Martian analogue denominated CAP-1 was collected during a geological survey of the Institute for Space Astrophysics and Planetology (IAPS), in October 2021. It was gathered in 120 cm-depth excavated trench in the area of Capalbio (Tuscany, Italy). It is a Pleistocene metasedimentary rock subjected to hydrothermal alteration/weathering (Figure 2). This brownish siltstone/mudstone is a quite compact rock in dry conditions and brittle in wet conditions. Inside it, there are a few discoidal, sub-angular grains with a diameter higher than 2 mm and different colors (black, reddish, and white), and low sphericity. Grains are not-oriented, except for black Manganese aggregates, which form thin veins with a diameter of about 2-5 mm. Other grains are white rectangular precipitations of Al-bearing clay (kaolinite) and reddish irregular aggregates formed by iron oxide (hematite). The brownish fine-grained (granulometry in the order of silt-clay) matrix has medium porosity, without cement. It lacks stratification and it shows possible alteration due to iron oxidation. CAP-1 is well-sorted, texturally and compositionally mature. The mineral assemblage of the CAP-1 sample is constituted of Mg/Fe smectite, kaolinite, illite, quartz, and minor calcite. It can contain some part of organic material based on analysis of similar soil in the area, but no detectable fossil evidence is found inside. Figure 2 – a) Outcrop where CAP-1 is extracted (sampling depth 30-75 cm); b) Sample Capalbio CAP-1; c) Details of CAP-1 taken under a microscope: Mn aggregates. Discussion and conclusions: Some preliminary acquisitions are taken using the DAVIS-MOT, as we can see in Figure 3. We acquire 3 random points on a planar surface of the sample. After that, raw data of spectra are smoothed and merged between 1075 and 1140 nm (the AVANTES spectrometer has two different detectors and the acquisitions are made for the VIS and IR in two steps). Resampling is done in 364 points between 400 and 2300 nm. Spectra show characteristic absorption bands of water at 1.4 and 1.9 µm, well-shaped absorption bands at 0.95 and 2.2 µm associated with iron transition and Al-OH bond respectively. A deep spectral analysis will be done after the new laboratory acquisition of this sample. Figure 3 – VIS-NIR CAP-1 spectra acquired by DAVIS-MOT. Acknowledgments: This work is supported by the Italian Space Agency (ASI) grant ASI-INAF n. 2017-412-H.0. Ma_MISS is funded by ASI and INAF. References: [1] De Sanctis, M. C. et al. (2017) Astrobiology, 17(6–7), doi: 10.1089/ast.2016.1541; [2] Davis, J. M. et al. (2016) Geology, 44(10), doi: 10.1130/G38247.1; [3] Quantin-Nataf, C. et al. (2021) Astrobiology, 21(3), doi: 10.1089/ast.2019.2191; [4] Mandon, L. et al. (2021) Astrobiology, 21(4), doi: 10.1089/ast.2020.2292; [5] Brossier, J. (2022) Icarus, accepted pending revisions; [6] Rossi, L. et al. (2022) LPSC 53, Abstract #1353, [7] De Angelis, S et al. (2022) LPSC 53, Abstract #1796.

In this work, we apply a method previously discussed in [1] to assess the presence of water ice in Mercury’s Polar Shadowed Regions (PSR) mixed to S-rich volatile species like SO2, H2S, and volatile organics, intending to verify their detectability from Bepi Colombo’s orbit and to optimize SIMBIO-SYS/VIHI observations. PSR icy deposits located within the floor of the Kandinsky crater are simulated in terms of I/F spectra corresponding to mixtures of H2O-H2S and H2O-SO2 with grain sizes of 10, 100, and 1000 µm as resulting from indirect illumination by the scattered solar light coming from the crater’s rim. The spectral simulations, performed following the method described in [2], and including the ice-regolith mixing (areal or intimate) as modeled in [3], allow for exploring different volatile species abundances and grain size distribution.The resulting ice detection threshold are evaluated by means of the computation of VIHI’s instrumental signal-to-noise ratio as given by the instrumental radiometric model [4]. In this way, a synergistic use of illumination models, spectral simulations and resulting SNR calculations will help us to optimize the VIHI’s observation strategy across Mercury’s polar regions with the aim to detect, identify and map volatile species. This task is one of the primary scientific goals of the 0.4-2.0 µm Visible and Infrared Hyperspectral Imager (VIHI) [5], one of the three optical channels of the SIMBIO-SYS experiment [6] on ESA’s BepiColombo mission.Due to orbital characteristics and proximity to the Sun, Mercury’s polar regions undergo large variations in illumination conditions during the hermean year [1]. At poles, Permanent Shadowed Regions (PSRs) occur on deep craters and rough morphology terrains that are not directly illuminated by the Sun during the hermean day. Nevertheless, some of these areas could experience partial illumination caused by multiple scattered light coming from nearby illuminated areas. Despite the orbital vicinity to the Sun, Mercury’s PSRs can maintain cryogenic temperatures across geological timescales resulting in the condensation and accumulation of volatile species [7]. While water ice is the more certain species in Mercury’s PSR, it is not precluded the occurrence of other secondary species rich in sulfur or even organic matter.In fact, the total surface area of PSRs between latitudes 80−90° south is not negligible, being estimated at about 25.000 km2 [8], about two times larger than the same geographic area on the North Pole [9]. References: [1] Filacchione G. et al., MNRAS, 498, 1308-1318, 2020. [2] Raponi A. et al., Sci. Adv., 4, eaao3757, 2018. [3] Ciarniello. M. et al., Icarus, 214, 541, 2011. [4] Filacchione G. et al., Rev. Sci. Instrum., 88, 094502, 2017. [5] Capaccioni F. et al., IEEE Trans. Geosci. Remote Sens., 48, 3932, 2010. [6] Cremonese G. et al., Space Sci. Rev., 216, 75, 2020. [7] Paige D. A. et al., Science, 339, 300, 2013. [8] Chabot N. L. et al., J. Geophys. Res., 123, 666, 2018. [9] Deutsch A. N. et al., Icarus, 280, 158, 2016. Acknowledgments: We gratefully acknowledge funding from the Italian Space Agency (ASI) under ASI-INAF agreement 2017- 47-H.0.

Ceres is the largest body in the Main Belt, and it is characterized by a large abundance of water ice in its interior. This feature is suggested by its relatively low bulk density (2162 kg m−3), while its partial differentiation into a rocky core and icy crust is suggested by several geological and geochemical features: minerals and salts produced by aqueous alteration, icy patches on the surface, and lobate morphology interpreted as surface flows. In this work, we explore how the composition can influence the characteristics of thermal convection in the crust of Ceres. Our results suggest that the onset of thermal convection is difficult and when it occurs, it is short lived, which could imply that Ceres preserved deep liquid until present, as recently suggested by the work of Castillo-Rogez et al. Moreover, cryovolcanism could be driven by diapirism (chemical convection) rather than thermal convection.

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.

Introduction The selected landing site of the ExoMars mission (Oxia Planum) [1] shows mineralogical and morphological evidence that it was characterized by a hydrothermal history and by a long duration of aqueous superficial activity [2; 3]. These factors are consistent with conditions favourable to life development. In this framework, we planned a field campaign in the Rio Tinto [4] area (Europlanet TA1 facility 2) where to perform a set of VIS-NIR measurements using our portable spectrometer. In addition, for each analyzed mineral/rock on-field, we collect a representative sample to be measured with the Ma_MISS instrument laboratory model. Fig.1: TA1.2 Rio Tinto, south-west Spain a very acidic 100 km river with intense red dark colour (credits F. Gomez). The Ma_MISS instrument Ma_MISS is the Visible and Near-Infrared miniaturized spectrometer hosted in the drill system of the ExoMars rover that will characterize the mineralogy and stratigraphy of the excavated borehole wall at different depths (2O and hydrated phases; (3) characterize important optical and physical properties of the materials (e.g., grain size); (4) produce a stratigraphic column that will provide information on the subsurface geology. Ma_MISS will operate periodically during pauses in drilling activity and will produce hyperspectral images of the drill’s borehole. Field activity During the field campaign, we perform a set of VIS-NIR (0.35 – 2.5 μm) measurements using our ASD FieldSpec4 portable spectrometer on biosignatures-bearing rocks and acidic alteration products. For each selected lithotype we collect several reflectance spectra using solar light as the light source and a 99% Spectralon target as a reference in the VIS-NIR range, with particular attention to those that hypothetically host organic matter in the form of bacterial communities. In addition, for each measured mineral/rock we collect a representative sample to be used for the laboratory measurements with the Ma_MISS laboratory model. With this setup, it is possible to perform measurements with samples in different configurations (powders, slabs, or holed rock blocks); hence, we collect samples with different specific dimensions. In the case of incoherent sediments/salts, we sample a minimum amount of 20-30 g. On the contrary, in the case of coherent samples, we collect blocks with a maximum size of 10x10x10 cm, which are the optimal dimensions useful for performing the drilling operations and in-hole measurements with the DAVIS setup [6,7]. For each collected sample, we record the following data at the time of collection: imagery of the context and the sampling site with a reference scale, the three-dimensional orientation of the sample, and the geographic coordinates at the collection point using a GNSS dual-frequency GPS. Every sample is sealed in a specific container to avoid any contamination [8]. The samples’ metadata are registered in the System for Earth Samples Registration (SESAR) for long-term archival of the physical samples which can be retrieved from a unique ISGN code (isgn.org) for referencing in this and future projects. Laboratory activity The collected samples were measured with the DAVIS (Drill for Analogues and Visible-Infrared Spectrometer) setup at the INAF-IAPS laboratories. This laboratory facility is constituted by a drilling tool that reproduces the ExoMars Drill functionality (Laboratory Drill, LD [6]) and by a measurement tool, reproducing Ma_MISS optical characteristics (Ma_MISS Optical Tool, MOT [7]). Consisting of spare elements of the flight instrument, the DAVIS setup can be considered an instrument completely comparable to the one that will investigate the Martian subsurface. For this reason, the measurements on the collected samples become very important for instrument characterization and future data interpretation. The collected sample blocks are drilled to obtain a hole with the same characteristics as those that the ExoMars drill will do on Mars. Finally, we perform a series of in-hole spectral scans to characterize the chemical-physical properties of the collected samples. The data collected on-field and in the laboratory are analyzed and compared to reconstruct the composition of the analyzed samples. We will focus our efforts on any spectral signature related to the presence of biomarkers in the collected data since we know that the Ma_MISS tool can aid in detecting organics [9] in the Martian subsoil, which is one of the main scientific objectives of the ExoMars mission. Conclusions In this work, we describe the procedures followed during our geological field analysis campaign in the Rio Tinto area. This geologically/biologically well-documented site with its rock/water/biology interaction represents an ideal open-air laboratory where to collect spectral data and samples useful for testing the ExoMars/Ma_MISS spectrometer. The scientific results obtained by this and previous works made with other drilling equipment [10] and with other scientific instruments [11] confirm that this type of activity in the Rio Tinto area site is important for enriching the scientific community's grasp on the Martian environment and for obtaining key information on the mineralogical and geochemical evolution of the Martian surface/subsurface. In addition, this work provides crucial preparation for the exploitation and interpretation of the scientific data that the Ma_MISS instrument will supply during the active phase of the mission. This activity is also useful for defining the priorities of the astrobiological objectives on the ground. Acknowledgements This work is supported by the Italian Space Agency grant ASI-INAF n. 2017-412-H.0. Ma_MISS is funded by ASI and INAF. Europlanet 2024 RI has received funding from the European Union’s Horizon 2020 research and innovation programme under grant agreement No 871149. References [1]Vago, J.L. et al. (2017) Astrobiology; [2]Mandon, L. et al. (2021) Astrobiology; [3]Quantin-Nataf, C. et al. (2021) Astrobiology; [4]Amils, R. et al. (2014) Life; [5]De Sanctis, M.C. et al. (2017) Astrobiology; [6]Rossi, L. et al. (2022) 53rd LPSC #1353; [7]De Angelis, S. et al. 53rd LPSC (2022) #1796; [8]Cockell, C.S., et al. (2019) Space Sci Rev. [9]Ferrari, M. et al. (2020), EPSC2020-348; [10]Bonaccorsi, R. et al (2008) Astrobiology; [11]Gomez, F. et al., (2011) Int. J. Astrobiology.

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 current generation of rovers exploring Mars for traces of life feature tools for subsurface sampling capabilities. This addition to the sampling capabilities of the martian rovers is crucial for the search for life. In fact, in the subsurface life is more likely to be protected from the harsh radiation environment present on the surface. The sampling of subsurface materials started with the analysis of the first millimeters of unweathered rocks being pulverized or abraded (NASA/MSL), evolved with the extraction of small cores from the first 10 centimeters (NASA/Mars2020), and will continue with the exploratory drilling of ESA's ExoMars 2022 which is capable of reaching 2 meters of depth. The proper planning and interpretation of measurements below the topographic surface require a model of the subsurface. Geological models are digital representations of subsurface structures generated by the sequence in time of processes putting in place different rocks and terrains. Geologic cross-sections are an example of bi-dimensional modeling that extends observations taken at the surface. Modern geologic models are commonly developed in three dimensions and used for terrestrial resource exploration, seismic analyses, and hydrologic simulations. The key to a good geologic model is the integration of measurements taken by different instruments. For ExoMars 2022, observations at the surface will be extended at depth by the spectrometer Ma_MISS which will read the mineralogical composition down to two meters, and the radar WISDOM which will collect geophysical images of the terrain down to ten meters or more. In this work, we explore different methods to generate geological models of the subsurface of areas at Oxia Planum and a selection of analog outcrops at different scales.

Monitoring of vibrational eigenmodes of an elastic body excited by gravitational waves was one of the first concepts proposed for the detection of gravitational waves. At laboratory scale, these experiments became known as resonant-bar detectors first developed by Joseph Weber in the 1960s. Due to the dimensions of these bars, the targeted signal frequencies were in the kHz range. Weber also pointed out that monitoring of vibrations of Earth or Moon could reveal gravitational waves in the mHz band. His Lunar Surface Gravimeter experiment deployed on the Moon by the Apollo 17 crew had a technical failure rendering the data useless. In this article, we revisit the idea and propose a Lunar Gravitational-Wave Antenna (LGWA). We find that LGWA could become an important partner observatory for joint observations with the space-borne, laser-interferometric detector LISA, and at the same time contribute an independent science case due to LGWA's unique features. Technical challenges need to be overcome for the deployment of the experiment, and development of inertial vibration sensor technology lays out a future path for this exciting detector concept., 29 pages, 17 figures

The ExoMars Rover and Surface Platform planned for launch in 2022 is a large international cooperation between the European Space Agency and Roscosmos with a scientific contribution from NASA. Thales Alenia Space is the ExoMars mission industrial prime contractor. Besides sensors and instruments characterizing the surface at large scale, the ExoMars’ rover Rosalind Franklin payload features some experiments devoted specifically to the characterization of the first few meters of the Martian subsurface. These experiments are particularly critical for the main ExoMars objective of detecting traces of present or past life forms on Mars, which may have been preserved within the shallow Martian underground [1]. Rosalind Franklin will be able to perform both non-invasive geophysical imaging of the underground [2] and subsurface in situ measurements thanks to the Drill unit installed on the rover. The Drill has been developed by Leonardo and its purposes are 1) to collect core samples to be analyzed in the Analytical Laboratory Drawer (ALD) onboard the Rover and 2) to drive the miniaturized spectrometer Ma_MISS within the borehole. Ma_MISS (Mars Multispectral Imager for Subsurface Studies, [3]) will collect mineralogic measurements from the rocks exposed into the borehole created by the Drill with a spatial resolution of 120 μm down to 2 meters into the Martian subsurface. Rocks are composed of grains of minerals, and their reaction to an applied stress is related to the mechanical behavior of the minerals that compose the rock itself. The mechanical properties of a mineral depend mainly on the strength of the chemical bonds, the orientation of crystals, and the number of impurities in the crystal lattice. In this context, the integration of Ma_MISS measurements and drill telemetry are of great importance. The mechanical properties of rocks coupled with their mineralogic composition provide a rich source of information to characterize the nature of rocks being explored by ExoMars rover’s drilling activity. Within our study, we are starting to collect telemetry recorded during the Drill unit tests on several samples ranging from sedimentary to volcanic rocks with varying degrees of weathering and water content. In this first phase of the study, we focused our attention on the variation of torque and penetration speed between different samples, which have been found to be indicative of a particular type of rock or group of rocks and their water content. We are planning to analyze the same rocks with the Ma_MISS breadboard creating the link between the mineralogy and the mechanical response of the Drill. This will put the base for a more comprehensive and rich characterization of the in situ subsurface observation by Rosalind Franklin planned at Oxia Planum, Mars in 2023. Acknowledgments: We thank the European Space Agency (ESA) for developing the ExoMars Project, ROSCOSMOS and Thales Alenia Space for rover development, and Italian Space Agency (ASI) for funding the Ma_MISS experiment (ASI-INAF contract n.2017-48-H.0 for ExoMars MA_MISS phase E/science). References [1] Vago et al., 2017. Astrobiology, 17 6-7. [2] Ciarletti et al., 2017. Astrobiology, 17 6-7. [3] De Sanctis et al., 2017. Astrobiology, 17 6-7.

Introduction Alteration of mafic and ultramafic rocks on Mars surface and shallow subsurface has been postulated to have occurred throughout its history by means of different mechanisms, among which acid groundwater circulation (mainly sulfuric) is one of the most important [1,2,3,4]. This hypothesis is based on the high Fe and S concentration observed at various landing sites and strengthened by remote-sensing infrared detection of Fe/Al-bearing sulfates such as alunite, jarosite and Fe3+SO4(OH) [4,5]. These sulfates typically form as alteration of K-rich volcanic rocks and Fe-sulfides in low-pH environments. Additionally the occurrence of perchlorates could be related to the action of other acids (perchloric) [6]. The investigation in laboratory of acidic alteration of volcanic rocks is thus an essential step in order to provide constraints in the interpretation of remote-sensing and in-situ data from Mars missions of the next future (Mars-2020, ExoMars-2022). Several works recently have explored the processes of acid alteration of minerals and rocks both in the field and in laboratory by using different spectroscopic and microscopy techniques [7,8]. Methods In our work we studied by Visible-Near Infrared reflectance and Raman spectroscopy the acid alteration of two volcanic samples, a basalt from Aeolian Islands (FCD1) and a rhyodacite from Alps (RDO). These two samples have been chosen with the aim of investigating the action of acids on both a mafic and a felsic rock. Four acids have been used for the treatment of samples, namely hydrochloric (HCl 37 vol%), nitric (HNO3 65 vol%), sulfuric (H2SO4 96 vol%) and phosphoric (H3PO4 85 vol%), in order to contemplate a diversity of acid environments. Samples were acid-treated both in the form of fine powders (d VIS-NIR reflectance spectroscopy measurements were carried on with ASD FieldSpec-4 spectro-photometer coupled with a QTH lamp and optical fibers (i=30°, e=0°), in the 0.35-2.5-μm range, using LabSphere Spectralon as reference. The spectral sampling was 3-8 nm, and the spatial resolution about 6 mm. Raman spectroscopy data were acquired with a Bruker-Senterra II spectrometer, with a 532 nm excitation laser, a power of 50 mW, 4 cm-1 spectral resolution, and about 5 mm of spatial resolution. Raman data were acquired on pre- and post-treatment slab samples. Results VIS-NIR. We present preliminary results of our experiments. Example of VIS-NIR spectra are shown in fig.1 for the basalt FCD1. The spectrum of pre-treated basalt (black curve, fig.1) is characterized by iron absorption features at 0.52 μm and 1 μm (faint), with a blue slope below 1.5 μm and a red slope above 1.5 μm. Although the effect due to some hydration is unavoidably present in the treatment, nevertheless the different acids produce different results. The overall spectral shape does not change much after treatment with HCl and HNO3, although new absorption features appear or increase in intensity. In the HCl-treated sample the 1-μm band is notably more marked than the pre-existing one, and new features appear at 1.44, 1.60, 1.75, 1.93, 2.15 and 2.24 μm. Although especially the ~1.4 and ~1.9-μm bands are related to hydration in the sample or to some new hydrated phase, nevertheless these new bands indicate the appearance of new mineralogical phases. For example some of these bands are reported to occur in hydrated Na-perchlorates [9]. Curiously in the HCl-treated sample the ~0.5-μm feature seems to disappear. In the H2SO4-treated sample the overall spectral slope is changed from red to blue, and only two hydration bands appear. In the HNO3-treated sample a new weak band appeared around 2.23 μm. Raman. The Raman spectra of an alkali-feldspar phenocryst of the rhyodacite sample (RDO) collected pre- and post-treatment with HNO3 are displayed in fig.2 (black and red, respectively). The spectrum of the untreated sample is characterized by the typical Raman peaks of the alkali-feldspar. On the contrary, in the spectrum of the acid-treated sample, the appearance of the peaks at 1053 and 715 cm-1 indicate the formation of niter (NaNO3) in the same areas of the sample where the alkali-feldspar is present. Conclusions Visible-infrared and Raman analyses of both mafic and felsic volcanic rocks treated with different acids have shown the appearance of new absorption bands and changes in spectral shapes, indicating the formation of new mineralogical phases. While Raman data clearly indicate the presence of precise minerals, the interpretation of VIS-NIR spectra is not straightforward. Further analyses will be conducted both on the powders and slabs in order to recognize the new mineralogical phases, to discriminate between the alteration action of acid solution and water alone, and to disentangle the effects of the different acids over time. Acknowledgements This work is funded by ASI. We thank A.Pisello from University of Perugia for providing the rhyodacite sample. References. [1] Burns R.G., Journal of Geophysical Research, vol.92, n.B4, pp.E570-E574, 1987 [2] Burns R.G., 19th Lunar and Planetary Science Conference, 46-47, 1988 [3] Burns R.G. and Fisher D.S., Journal of Geophysical Research, vol.95, n.B9, pp.14,415-14,421, 1990 [4] Hurowitz J.A. and McLennan S.M., Earth and Planetary Science Letters, 260, 432, 443, 2007 [5] Ehlmann B.L. and Edwards C.S., Annu. Rev. Earth Planet. Sci., 42, 291-315, 2014 [6] Wilson E.H., Journal of Geophysical Research:Planets, 121, pp.1472-1487, 2016 [7] Gurgurewicz J. et al., Planetary and Space Science, 119, 137-154, 2015 [8] Smith R. et al., Journal of Geophysical Research:Planets, 122, pp.203-227, 2017 [9] Hanley J. et al., Journal of Geophysical Research:Planets, 119, pp.2370-2377, 2014

We studied the dust activity of comet 67P/Churyumov-Gerasimenko (67P), by relating the detections of the Rosetta/ GIADA and MIDAS instruments, obtaining a correlation between flux of ejected mm- and μm-sized dust. Introduction The ESA/Rosetta mission orbited the 67P comet for two years, escorting it through perihelion, occurred on 13th August 2015. The mission configuration is still permitting a thorough characterization of cometary activity, even 4 years from the end of the mission. In particular, the 67P’s dust ejection has been detected in different stages of the comet’s orbit by both remote observations (e.g., the OSIRIS camera and the VIRTIS imaging spectrometer) and in-situ measurements performed by detectors as GIADA, MIDAS and COSIMA. This work merges data from the GIADA (Grain Impact Analyser and Dust Accumulator) [1] dust detector and the MIDAS (Micro-Imaging Dust Analysis System) [2] atomic force microscope. The two instruments detected dust different in size (mm-sized vs μm-sized) and complementary dust properties (porosity and mass vs physical properties and 3D structure). The GIADA and MIDAS data fusion could allow to relate ejection of smaller and larger dust particles as well as to monitor variations of dust properties during Churyumov-Gerasimenko’s orbit and to link them to the morphology of ejecting surface regions. Data 2.1 The GIADA dataset The GIADA instrument consists of three subsystems: Grain Detection System (GDS), Impact Sensor (IS) and Quartz Crystal Microbalances (QCM). The first two subsystems measured velocity of fluffy particles and momentum of compact (mm-sized) particles, respectively, whereas the QCM measured the cumulative mass of nm-sized dust [3]. To compare GIADA and MIDAS dataset, we considered only the IS data, because MIDAS mostly detected individual compact particles. In particular, we considered only the IS detections acquired in the periods when MIDAS detected dust particles (see next subsection). [4] developed a procedure to trace back the motion of dust particles detected by GIADA in the coma down to the nucleus surface. This allowed the retrieval of the geomorphological region ejecting each dust particle and the association of dust and surface properties. These results are intended to be extended to the GIADA-MIDAS data fusion to relate dust physical properties and surface morphology. 2.2 The MIDAS dataset MIDAS collected micron-sized dust particles on several targets, each working in a defined period. Cometary dust was detected on four MIDAS targets: Target 10, Target 12 and Target 14 collected dust in three periods before perihelion (September-November 2014, December2014-February 2015 and February-March 2015, respectively), whereas the dust collected on Target 13 was released in an outburst on 19th February 2016 (after perihelion). Except one case of a fluffy agglomerate [5], all the particles detected by MIDAS are compact. Method and preliminary results 3.1 mm- vs μm- sized dust flux Our first step was to compare the millimetric and micrometric dust flux measured by GIADA-IS and MIDAS, respectively. For each period corresponding to the collection time of a MIDAS target, we retrieved the number of particles detected by the two instruments, normalized it to the period duration (in days) and to the spacecraft-comet distance (in km). The MIDAS flux required an additional normalization, taking into account the scanned area on the respective target (not constant among targets). The comparison of dust fluxes measured by GIADA and MIDAS is shown in Figure 1. Figure 1. Dust fluxes measured by MIDAS and GIADA. Each asterisk corresponds to a MIDAS target, i.e., to a defined orbit period. The red asterisk corresponds to MIDAS Target 14 (which detected dust between February and March 2015). The flux logarithms are linearly related, suggesting a strong correlation between ejection of large (mm-sized) and small (mm-sized) compact dust agglomerates. The flux corresponding to the MIDAS Target 14 period (February/March 2015), highlighted in red in Figure 1, is slightly outside this linear trend, with GIADA (MIDAS) detecting more (less) particles than expected from the linear trend identified by the other three periods. This can be ascribed to the occurrence of an outburst (detected by GIADA but not by MIDAS) in a moment when the spacecraft had the largest distance to the comet among all herein considered periods. As smaller particles are stronger deviated from their initially radial trajectory than larger ones (due to the more important role of solar pressure force with respect to nucleus gravity [6]), it is reasonable that fewer small than large particles arrived at the spacecraft position. However, this result needs further refinement regarding a possible falsification of MIDAS particle size distribution caused by particle fragmentation upon collection. Our next steps are to discern parent particles and fragments in the MIDAS data set and to update the relation shown in Figure 1. This will be done by analyzing the spatial distribution of dust particles on the MIDAS targets, by comparing MIDAS’ dust size distribution to that expected during nominal activity [7] and during outbursts [8] and by taking into account the largest dust size expected to be ejected depending on the nucleus surface temperature [9]. 3.2 Dust vs surface properties By applying the traceback algorithm developed by [4], we obtained that in certain periods dust is mostly ejected from rough or from smooth terrains. Therefore, we can relate properties of particles stemming from different locations at the comet to cometary surface morphology. In addition, dust ejected during outbursts may probe deeper layers of the comet, allowing us to discern dust properties at different depths. Acknowledgements This research was supported by the Italian Space Agency (ASI) within the ASI-INAF agreement I/032/05/0, by the Austrian Science Fund FWF P 28100-N36, and by the International Space Science Institute (ISSI) through the ISSI International Team “Characterization of cometary activity of 67P/Churyumov-Gerasimenko comet”. References [1] Della Corte, V. et al. (2014) JAI 1350011-1350022; [2] Bentley, M.S. et al. (2016), Acta Astronautica 125; [3] Della Corte, V. et al. (2019), A&A 630, A25, 13 pp.; [4] Longobardo, A. et al. (2020), MNRAS 496, 1, 125-137; [5] Mannel, T. et al. (2016), MNRAS 462; [6] Zakharov, V.V. et al. (2018), Icarus, 312, 121-127; [7] Rinaldi, G. et al. (2016), MNRAS 462, 1, S547-S561; [8] Bockelée-Morvan, D. et al. (2017), MNRAS, 469 2, S443-S458; [9] Fulle, M. et al. (2020), MNRAS, 493, 4039-4044.

We performed thermophysical simulations of Oxia Planum, the landing site of the ExoMars 2022 mission [5]. The numerical simulations concern: I) the influence of the thermal inertia on the subsurface temperature at the latitude of Oxia Planum; II) the heat released in the subsurface by the drill installed on the ExoMars rover. The numerical simulations are performed using a 3-D model using the discretization technique of the finite element method (FEM). 1. Introduction Numerical simulations are required to characterize, from a thermophysical point of view, Oxia Planum, the landing site of the mission ExoMars 2022. A drilling system is installed on the ExoMars rover and it will be able to analyze up 2 meters in the subsurface of Mars. The spectrometer Ma_Miss (Mars Multispectral Imager for Subsurface) [1] will investigate the lateral wall of the borehole generated by the drill, providing hyperspectral images. Among the scientific objectives of Ma_Miss there are the characterization and the mapping of possible volatiles. In this regard, numerical simulations are useful to understand if the temperatures in the subsurface are such as to preserve volatiles, especially after the heating provided during the drilling operations. 2. Numerical Method We performed our simulations by using a 3-D finite element model [2, 3], which solves the classical heat equation in a parallelepipedal domain representing a portion of Oxia Planum, the landing site of the ExoMars mission. The top of this domain is modeled with a Gaussian random surface in order to simulate the roughness of the surface. The dimensions of the domain are 1cm x 1cm x 5cm. The depth (5 cm) has been chosen since it is compatible with the likely skin depth. At the top we imposed a radiationboundary condition, while on the other sides zero heat flux is imposed. The initial temperature is set at 200 K, which is compatible with the surface equilibrium temperature. Self-heating between the facets of our domain is taken into account. We investigate: I) the dependence of the subsurface thermal response to different thermal inertia; II) theheat released by the drill in the subsurface of Mars. In particular, for the point II, we assume: a) the drilling is instantaneous in a well-defined “drilling temporal window”; b) thrust and rotational velocity are constant. The contribution of the drill is taken into account by applying an heat flux (depending in particular on the thrust, angular velocity and frictional heating) on the wall of the rock matrix in contact with the drill. 3. Summary and conclusions In Fig.1 we report an example of the results we obtained by applying our numerical model. Fig.1 shows the temperature profile vs time at different depths for two cases: case Fig.1: Temperature profile vs time at different depths. Case (A): K = 0.045 W m−1K−1; Case (B) K = 0.0045 W m−1K−1. (A) with a thermal conductivity K=0.045 W m-1 K-1, compatible with Insight estimation [4] and case (B) with a thermal conductivity an order of magnitude smaller than the case (A). Case (A) is characterized by a thermal inertia of 270 TIU (Thermal Inertia Units) and a skin depth of 3 cm, while case (B) is characterized by a thermal inertia of 85 TIU and a skin depth less than 1 cm. Our numerical results suggest that: a) the surface temperature ranges from 180 K to 270 K if thermal inertia is high (300 TIU); b) surface temperature ranges from 140 K to 280 K if thermal inertia is low ( Fig.2: Left panel: rpm = 30 and η= 0.5; right panel: pm = 60 and η= 0.9. Acknowledgements The Italian Space Agency (ASI) has founded the experiment. References [1] Coradini, A., et al.: MA_MISS: Mars multispectralimager for subsurface studies, Advances in Space Research, Volume 28, Issue 8, p. 1203-1208, 10.1016/S0273-1177(01)00283-6, 2001 [2] M. Formisano, M.C. [De Sanctis], S. [De Angelis], J.D. Carpenter, and E. Sefton-Nash. Prospecting the moon: Numerical simulations of temperature and sublimation rate of a cylindric sample. Planetary and Space Science, 169:8 – 14, 2019. [3] Rinaldi, G., Formisano, M., Kappel et al., Analysis of night-side dust activity on comet 67p observed by virtis-m: a new method to constrain the thermal inertia on the surface. A&A, 630:A21, 2019. [4] T. Spohn et al. The Heat Flow and Physical Properties Package (HP3) for the InSight Mission, Space Science Reviews volume 214, Article number: 96 (2018) [5] Vago et al., 2017. Astrobiology, 17 6-7

Laboratory measurements were performed on different mixtures made with clays and organic compounds with the aim of characterizing the detection capabilities of biosignatures by the Ma_MISS (Mars Multispectral Imager for Subsurface Studies) instrument. Introduction The main scientific objectives of the ESA mission ExoMars2022 are searching for signs of past and/or present life on Mars and characterizing the subsurface geochemical environment as a function of depth. The Rosalind Franklyn rover [1] payload consists of a suite of nine instruments that will provide information about the geological and geochemical environment of the surface and subsurface of the selected landing site (i.e. Oxia Planum) [2]. Remote sensing measurements performed by OMEGA and CRISM suggest that the exposed rocks on the surface of Oxia Planum experienced an intense aqueous alteration [3]. The widespread presence of Fe/Mg-Al-phyllosilicates and, more generally, the presence of silicates containing OH confirm the interaction between water and mother rocks, which is a prerequisite favorable to the development of life. In this framework, we performed several spectroscopic measurements of clay minerals mixed with different organic compounds, to assess Ma_MISS capability of organic’s detection in the Martian subsurface. The Ma_MISS instrument Ma_MISS is the Visible- and Near-Infrared miniaturized spectrometer hosted in the drill system of the ExoMars2022 rover that will characterize the mineralogy and stratigraphy of the excavated borehole wall at different depths (2O and hydrated phases; (3) characterize important optical and physical properties of the materials (e.g., grain size); (4) produce a stratigraphic column that will provide information on the subsurface geology. Ma_MISS will operate periodically during pauses in drilling activity and will produce hyperspectral images of the drill’s borehole. Experimental setup The characterization of the scientific performances of the Ma_MISS instrument was made using the laboratory model (breadboard, Fig. 1 [5], [6]) at the Institute for Space Astrophysics and Planetology – INAF. The Ma_MISS breadboard includes the 5 W light source, the optical fibers, and the Optical Head with the dual task of focusing the light on the target and recollecting the scattered light. However, it does not include the flight spectrometer and is therefore coupled with a laboratory spectrometer (FieldSpec 4). Fig. 1: Ma_MISS breadboard setup. A: Ma_MISS Optical Head; B: sample holder. Clay/organic mixtures measurements For these tests we prepared numerous samples mixing two clay minerals (nontronite and kaolinite) with four different organic compounds (asphaltite, glycine, benzoic acid, and polyoxymethylene). In particular, starting from the pure clay endmembers we tested two cases. In the first case, we added separately asphaltite and glycine in the following percentages: 25, 50, and 75, producing six different samples with high organics concentration. In the second case, we added separately benzoic acid and polyoxymethylene in percentages of 1, 5, and 10% preparing a set of six samples at a low concentration of organics. All mixtures with a grain size < 60 μm were measured using the Ma_MISS breadboard setup collecting reflectance spectra in the range 0.5–2.3 μm. Figure 2 shows an example of the data collected on the mixtures between kaolinite and glycine. Starting from the spectra of the pure clay (kaolinite 100%, black spectrum in Fig.2) and increasing the content of glycine by step of 25 wt.%, the band at 1.4 μm associated to the presence of the OH bond in kaolinite decreases. At the same time the band at 2.1–2.2 μm linked to the Al–OH bond in kaolinite become wider and much stronger due to the superimposition of the wider CH band of glycine at 2.1–2.25 μm. Other mixtures with other types of organics in a concentration below the 1% are still in preparation with the aim of determining the lower detection limit of the instrument in the function of the different hosting minerals. In these tests, we used glycine and other organic compounds, as examples of organic compounds that show absorption features in the VIS-NIR range, although we do not expect to find these specific organics in the Martian subsurface. Fig. 2: Example of Ma_MISS breadboard measurements of mineral/organic mixtures (kaolinite-glycine) in variable proportion. Conclusions Laboratory investigations have been performed using the Ma_MISS breadboard model (coupled with a FieldSpec Pro) on mineral/organic mixtures in different proportions. Spectroscopic measurements collected on these mineral/organic mixtures are useful to characterize Ma_MISS instrument sensitivity in detecting traces of life intimately mixed with minerals that could be present in sedimentary sequences or in hydrothermal products in the Martian subsurface, which is one of the main scientific objectives of the ExoMars2022 mission. The obtained results show that the Ma_MISS instrument can give hints of the presence of organics in the Martian subsoil, as well as characterizing the mineralogy of the drilling site. Moreover, the selected minerals and organic compounds allow us to test the instrument with both dark and bright samples. The spectra obtained during these tests will allow us to build a spectral database useful for the interpretation of the scientific data. Acknowledgments We thank the European Space Agency (ESA) for the ExoMars Project, ROSCOSMOS and Thales Alenia Space for rover development, and Italian Space Agency (ASI) for funding and fully supporting Ma_MISS experiment. References [1] Vago J.L. et al. (2017): Astrobiology, 17, 6, 7. [2] Quantin C. et al (2016) #2863, 47th LPSC, Houston, TX. [3] Carter J. et al. al (2016) #2064, 47th LPSC, Houston, TX. [4] De Sanctis M.C. et al. (2017): Astrobiology, 17, 6, 7. [5] De Angelis S. et al. (2014): PSS, 101, 89-107. [6] De Angelis S. et al. (2017): PSS, 144, 1-15.

The European Space Agency’s Rosetta mission1 has acquired unprecedented measurements of the surface of the nucleus of comet 67P/Churyumov–Gerasimenko (hereafter, 67P), the composition of which, as determined by in situ and remote-sensing instruments, including the VIRTIS instrument2, seems to be an assemblage of ices, minerals and organic material3. We performed a refined analysis of infrared observations of the nucleus of 67P carried out by the VIRTIS-M hyperspectral imager. We find that the overall shape of the infrared spectrum of 67P is similar to that of other carbon-rich outer Solar System objects, suggesting a possible genetic link with them. More importantly, we also confirm the complex spectral structure of the wide 2.8–3.6 µm absorption feature populated by fainter bands. Among these, we unambiguously identify the presence of aliphatic organics by their ubiquitous 3.38 µm, 3.42 µm and 3.47 µm bands. This infrared detection of aliphatic species on a cometary surface has strong implications for the evolutionary history of the primordial Solar System and is evidence that comets provide an evolutionary link between interstellar material and Solar System bodies4. A refined analysis of infrared observations of comet 67P/Churyumov–Gerasimenko from the VIRTIS instrument on board the Rosetta spacecraft has revealed the presence of aliphatic organic molecules on the comet nucleus.

Solar heating of a cometary surface provides the energy necessary to sustain gaseous activity, through which dust is removed1,2. In this dynamical environment, both the coma3,4 and the nucleus5,6 evolve during the orbit, changing their physical and compositional properties. The environment around an active nucleus is populated by dust grains with complex and variegated shapes7, lifted and diffused by gases freed from the sublimation of surface ices8,9. The visible colour of dust particles is highly variable: carbonaceous organic material-rich grains10 appear red while magnesium silicate-rich11,12 and water-ice-rich13,14 grains appear blue, with some dependence on grain size distribution, viewing geometry, activity level and comet family type. We know that local colour changes are associated with grain size variations, such as in the bluer jets made of submicrometre grains on comet Hale–Bopp15 or in the fragmented grains in the coma16 of C/1999 S4 (LINEAR). Apart from grain size, composition also influences the coma’s colour response, because transparent volatiles can introduce a substantial blueing in scattered light, as observed in the dust particles ejected after the collision of the Deep Impact probe with comet 9P/Tempel 117. Here we report observations of two opposite seasonal colour cycles in the coma and on the surface of comet 67P/Churyumov–Gerasimenko through its perihelion passage18. Spectral analysis indicates an enrichment of submicrometre grains made of organic material and amorphous carbon in the coma, causing reddening during the passage. At the same time, the progressive removal of dust from the nucleus causes the exposure of more pristine and bluish icy layers on the surface. Far from the Sun, we find that the abundance of water ice on the nucleus is reduced owing to redeposition of dust and dehydration of the surface layer while the coma becomes less red. Spectral analysis of the VIRTIS dataset shows two opposite seasonal colour cycles in the coma and on the surface of comet 67P/Churyumov–Gerasimenko, indicating an orbital water-ice cycle.

We characterized the 67P/Churyumov–Gerasimenko’s dust activity, by analysing individual dust particle velocity and momentum measurements of Grain Impact Analyser and Dust Accumulator (GIADA), the dust detector onboard the ESA/Rosetta spacecraft, collecting dust from tens to hundreds of kilometres from the nucleus. Specifically, we developed a procedure to trace back the motion of dust particles down to the nucleus, identifying the surface’s region ejecting each dust particle. This procedure has been developed and validated for the first part of the mission by Longobardo et al. and was extended to the entire GIADA data set in this work. The results based on this technique allowed us to investigate the link between the dust porosity (fluffy/compact) and the morphology of the ejecting surface (rough/smooth). We found that fluffy and compact particles, despite the lack of correlation in their coma spatial distribution (at large nucleocentric distances) induced by their different velocities, have common ejection regions. In particular, the correlation between the distributions of fluffy and compact particles is maintained up to an altitude of about 10 km. Fluffy particles are more abundant in rough terrains. This could be the result of past cometary activity that resurfaced the smooth terrains and/or of the comet formation process that stored the fluffy particles inside the voids between the pebbles. The variation of fluffy particle concentration between rough and smooth terrains agrees with predictions of comet formation models. Finally, no correlation between dust distribution on the nucleus and surface thermal properties was found.

The surface and internal structure of Ceres show evidence of a global process of aqueous alteration, indicating the existence of an ocean in the past. However, it is not clear whether part of this ocean is still present and whether residual fluids are still circulating in the dwarf planet. These fluids may be exposed in a geologically young surface, and the most promising site to verify the occurrence of present fluids on Ceres is Cerealia Facula dome, in Occator crater. This very young facula exhibits minerals that are relatively rare in our Solar System, the formation of which requires the presence of liquid water in combination with hydrothermal activity. Here we report the discovery of hydrated sodium chloride on Cerealia Facula. These newly identified chloride salts are concentrated on the top of the dome, close to a system of radial fractures. The spatial distribution of the hydrated phase suggests that chloride salts are the solid residue of deep brines that reached the surface only recently, or are still ascending. These salts are very efficient in maintaining Ceres’s warm internal temperature and lowering the eutectic temperature of the brines, in which case ascending salty fluids may exist in Ceres today. Spectroscopic data obtained at high spatial resolution from Dawn detected the presence of fresh chloride salts at Cerealia Facula on Ceres. The spatial distribution of the hydration level of these salts suggests that they surfaced a maximum of a few centuries ago and that the upwelling of salty fluids may still be active.

Thermal inertia is a key information to quantify the physical status of a planetary surface; it can be retrieved by comparison between theoretical and observed temperature diurnal profiles. We have calculated the surface temperature for a set of locations on Ceres' surface with a thermophysical model that provides temperature as a function of thermal conductivity and roughness, and we have determined the values of those parameters for which the best fit with the observed data is obtained. The observed temperatures have been retrieved form spatially-resolved data from the Dawn mission. In our previous work [Rognini et al., 2019], we have found that the average thermal inertia for the overall surface of Ceres is low (from 1 to 15 to 60 ​J ​m−2 ​s−½ K−1), as expected according to the general trend observed in the Solar System for atmosphere-less bodies, while the thermal inertia of the very bright faculae found in the floor of the Occator crater could not be well defined. Using more recently acquired VIR high resolution data we find that the central part of the Cerealia facula displays a thermal anomaly ( ~ 10 K above the average) compatible with a higher thermal inertia with respect to the surrounding regions, while the Vinalia facula does not display any consequently could have a grain size comparable with the Ceres’ surface average.

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.

Rosetta observes sublimating surface icesComets are “dirty snowballs” made of ice and dust, but they are dark because the ice sublimates away, leaving some of the dust behind on the surface. The Rosetta spacecraft has provided a close-up view of the comet 67P/Churyumov-Gerasimenko as it passes through its closest point to the Sun (see the Perspective by Dello Russo). Filacchioneet al.detected the spectral signature of solid CO2(dry ice) in small patches on the surface of the nucleus as they emerged from local winter. By modeling how the CO2sublimates, they constrain the composition of comets and how ices generate the gaseous coma and tail. Fornasieret al.studied images of the comet and discovered bright patches on the surface where ice was exposed, which disappeared as the ice sublimated. They also saw frost emerging from receding shadows. The surface of the comet was noticeably less red just after local dawn, indicating that icy material is removed by sunlight during the local day.Science, this issue p.1563, p.1566; see also p.1536

International audience; K nowledge of the surface temperature distribution of a comet's nucleus proves to be of fundamental importance for a number of reasons: the evaluation of the thermophysical properties (thermal inertia and roughness, at several spatial scales), the characterization of the thermal behaviour of peculiar surface units (for example, local ice exposures, or inherently cold material units not to be confused with shaded areas), and for the understanding of the physical processes affecting the surface and the shallow subsur-face layers (for example, sublimation of volatile compounds). The distribution of surface temperatures of a cometary nucleus, closely measured by a spacecraft, can be compared with theoretical models meant to predict the thermophysical properties of the nucleus at various depths and with previous thermal observations carried out by both Earth-based and space-based telescopes, with the goal of validating and/or improving those models 1. Furthermore, the temporal evolution of the surface temperatures, primarily driven by insolation, is critical in triggering the activity of a comet, allowing the migration of volatile compounds from the interior of the nucleus and the production of gas and dust observable with different techniques 2. In the past, thermal surveys of minor bodies were carried out using ground-based and space-based facilities. However, due to the limited spatial resolution of those observations, in most cases the derived thermal properties were only global averages, and the determined temperatures were highly model dependent. Before Rosetta, direct measurements of cometary nuclei surface temperatures were obtained during short periods for a handful of comets, namely 1P/ Halley 3 , 19P/Borrelly 4 , 9P/Tempel 1 1 and 103P/Hartley 2 5 , with a maximum spatial resolution of approximately 30 m per pixel. Here we study the surface temperature distribution of the nucleus of comet 67P/Churyumov-Gerasimenko as derived by the Visible InfraRed and Thermal Imaging Spectrometer, Mapping channel (VIRTIS-M, hereafter VIRTIS) 6 in Rosetta's early global mapping phase after comet encounter. These data cover the pre-perihelion period from 1 August to 23 September 2014, when the heliocentric distance decreased from 3.62 to 3.31 au and the spacecraft was in the altitude range 61-13 km above the surface, resulting in a spatial resolution from approximately 15 to 3 m per pixel (most data showing a resolution of 13 to 15 m per pixel). In this period, the solar phase angle ranged from 17° to 93°, which Knowledge of the surface temperature distribution on a comet's nucleus and its temporal evolution at different timescales is key to constraining its thermophysical properties and understanding the physical processes that take place at and below the surface. Here we report on time-resolved maps of comet 67P/Churyumov-Gerasimenko retrieved on the basis of infra-red data acquired by the Visible InfraRed and Thermal Imaging Spectrometer (VIRTIS) onboard the Rosetta orbiter in 2014, over a roughly two-month period in the pre-perihelion phase at heliocentric distances between 3.62 and 3.31 au from the Sun. We find that at a spatial resolution ≤15 m per pixel, the measured temperatures point out the major effect that self-heating, due to the complex shape of the nucleus, has on the diurnal temperature variation. The bilobate nucleus of comet 67P also induces daytime shadowing effects, which result in large thermal gradients. Over longer periods, VIRTIS-derived temperature values reveal seasonal changes driven by decreasing heliocentric distance combined with an increasing abundance of ice within the uppermost centimetre-thick layer, which implies the possibility of having a largely pristine nucleus interior already in the shallow subsurface.

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 goal of the ESA Luna 27/PROSPECT instrument [1] is to extract and characterize a regolith sample from the lunar south polar region, investigating its physical and chemical properties. The main target is to characterize the abundance and distribution of water ice and other volatiles so the challenge is to preserve volatiles in samples during the drilling transfer and analysis. In this work we provided numerical simulations in order to predict the expected ice sublimation rates and inform the system's development. Simulations are characterized by different initial boundary conditions as well as thermodynamic parameters and carried out on a cylinder representing a lunar regolith sample of the south polar region.

We propose a new internal evolution model for the dwarf planet Ceres matching the constraints on Ceres' present internal state from the Dawn mission observations. We assume an interior differentiated into a volatile-dominated crust and rocky mantle, and with remnant brines in the mantle, all consistent with inferences from the Dawn geophysical observations. Simulations indicate Ceres should preserve a warm crust until present if the crust is rich in clathrate hydrates. The temperature computed at the base of the crust exceeds 220 K for a broad range of conditions, allowing for the preservation of a small amount of brines at the base of the crust. However, a temperature ≥250 K, for which at least 1 wt.% sodium carbonate gets in solution requires a crustal abundance of clathrate hydrates greater than 55 vol.%, a situation possible for a narrow set of evolutionary scenarios.

The NASA/Dawn mission has acquired unprecedented measurements of the surface of the dwarf planet Ceres, the composition of which is a mixture of ultra-carbonaceous material, phyllosilicates, carbonates, organics, Fe-oxides, and volatiles as determined by remote sensing instruments including the VIR imaging spectrometer. We performed a refined analysis merging visible and infrared observations of Ceres&rsquo, surface for the first time. The overall shape of the combined spectrum suggests another type of silicate not previously considered, and we confirmed a large abundance of carbon material. More importantly, by analyzing the local spectra of the organic-rich region of the Ernutet crater, we identified a reddening in the visible range, strongly correlated to the aliphatic signature at 3.4 &micro, m. Similar reddening was found in the bright material making up Cerealia Facula in the Occator crater. This implies that organic material might be present in the source of the faculae, where brines and organics are mixed in an environment that may be favorable for prebiotic chemistry.

A recent study of Fu et al. analysed the remaining magnetization in the eucrite meteorite Allan Hills A81001, which mostly likely has been produced during the cooling phase of the life of the asteroid Vesta, arguing that an ancient dynamo in the advective liquid metallic core could be set in. Using petrographic and paleomagnetic arguments, Fu et al. estimated a surface magnetic field of at least 2 μT. In this work, we verify the possibility that an early core dynamo took place in Vesta by analysing four different possible fully differentiated configurations of Vesta, characterized by different chondritic compositions, with the constraints on core size and density provided by Ermakov et al. We only incorporate the thermal convection, by neglecting the effects of the compositional convection, so our results in terms of magnetic Reynolds number and duration of the dynamo can be interpreted as a lower bound. The presence of a magnetic field would make Vesta a peculiar object of the Solar system, a `small-Earth', since it has also a differentiated structure like Earth and the magnetic field has preserved Vesta from the space weathering.

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.

Water absorption bands due to superficially adsorbed molecules often dominate the near-infrared spectra of particulate minerals and rocks, when measured in the laboratory in the reflectance mode. In order to remove this, the spectral effect is thus necessary to acquire spectra of samples in vacuum and at higher temperatures. With the aim to accomplish this task, we developed an environmental cell to perform infrared spectroscopic measurements at controlled pressure-temperature conditions. Currently the cell allows one to measure reflectance spectra in the temperature range from room values up to 300 °C (573 K), in the pressure range of 103-10-6 mbar. The acquisition of spectra continuously in two distinct phases, namely, during a preliminary pumping stage (at room T) and subsequently during a heating stage (in vacuum), permits to highlight and characterize separately the effect of pressure and temperature on infrared spectra.

Ice thermal stability on the surface of the dwarf planet Ceres is an important issue linked to the Herschel observations of water vapor around Ceres. One of these surficial ice deposits is located within the 20-km crater Juling (35°S, 168°E). The study of water ice exposure in this specific crater is particularly interesting because it has been observed that the water ice abundance changes on a time scale of a few months. To understand the ice behavior, we applied a 3-D finite element method thermophysical model to the study of Juling crater in order to determine the water ice sublimation rate. We use a detailed shape model of Ceres derived from optical imagery returned by the Framing Camera on board Dawn. We explore the effects of different heliocentric distances and different thermal inertia values, comparing our numerical predictions with the observational evidences returned by VIR and by the Herschel Space Observatory.

Recent observations of water emission around Ceres suggest the presence of an ice layer on or beneath the surface of this asteroid. Several mechanisms have been suggested to explain these plumes, among which cometary-like sublimation seems to be plausible, since there is a correlation between the magnitude of the emission and the change in the heliocentric distance along the orbit. In this work, we applied a comet sublimation model to study the plausible scenarios that match with Herschel observations of the water flux (1026 molecules s-1). Each scenario is characterized by a well-defined set of physical and orbital parameters. Moreover, a study of the dynamic evolution of the H2O plume has been performed, showing that an optically thin transient atmospheric envelope, with a typical timescale of some tens of days, can be maintained by the H2O surface emission. Our simulations could be useful theoretical support for the Dawn NASA mission by giving a better understanding of the physical conditions for water sublimation and ice stability.

Five decades of observations of Ceres suggest that the dwarf planet has a composition similar to carbonaceous meteorites and may have an ice-rich outer shell protected by a silicate layer. NASA’s Dawn spacecraft has detected ubiquitous clays, carbonates and other products of aqueous alteration across the surface of Ceres, but surprisingly it has directly observed water ice in only a few areas. Here we use Dawn Framing Camera observations to analyse lobate morphologies on Ceres’ surface and we infer the presence of ice in the upper few kilometres of Ceres. We identify three distinct lobate morphologies that we interpret as surface flows: thick tongue-shaped, furrowed flows on steep slopes; thin, spatulate flows on shallow slopes; and cuspate sheeted flows that appear fluidized. The shapes and aspect ratios of these flows are different from those of dry landslides—including those on ice-poor Vesta—but are morphologically similar to ice-rich flows on other bodies, indicating the involvement of ice. Based on the geomorphology and poleward increase in prevalence of these flows, we suggest that the shallow subsurface of Ceres is comprised of mixtures of silicates and ice, and that ice is most abundant near the poles. Despite evidence for an ice-rich outer shell, little water ice has been observed on the surface of Ceres. Lobate morphologies observed on Ceres that are increasingly prevalent towards the dwarf planet’s poles are consistent with ice-rich flows.

In this work we study the link between the evolution of the internal structure of Vesta and thermal heating due to 26Al and 60Fe and long-lived radionuclides, taking into account the chemical differentiation of the body and the affinity of 26Al with silicates. Differentiation takes place in all scenarios in which Vesta completes its accretion in less than 1.4 Ma after the injection of 26Al into the Solar Nebula. In all those scenarios where Vesta completes its formation in less than 1 Ma from the injection of 26Al, the degree of silicate melting reaches 100 vol. % throughout the whole asteroid. If Vesta completed its formation between 1 and 1.4 Ma after 26Al injection, the degree of silicate melting exceeds 50 vol. % over the whole asteroid but reaches 100 vol. % only in the hottest, outermost part of the mantle in all scenarios where the porosity is lower than 5 vol. %. If the formation of Vesta occurred later than 1.5 Ma after the injection of 26Al, the degree of silicate melting is always lower than 50 vol. % and is limited only to a small region of the asteroid. The radiation at the surface dominates the evolution of the crust which ranges in thickness from 8 to about 30 km after 5 Ma: a layer about 3-20 km thick is composed of primitive unmelted chondritic material while a layer of about 5-10 km is eucritic., Comment: 22 pages, 3 tables, 6 figures. Accepted for publication on Meteoritics and Planetary Science, Special Issue for the Dawn Mission on the composition of 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

In this article, we study the possibility that Ceres has, or had in the past, a crust heavier than a pure or muddy ice mantle, in principle gravitationally unstable. Such a structure is not unusual in the Solar system: Callisto is an example. In this work, we test how the composition (I.e. the volumetric quantity of ice) and the size of the crust can affect its survival during thermo-physical evolution after differentiation. We have considered two different configurations: the first characterized by a dehydrated silicate core and a mantle made of pure ice, the second with a hydrated silicate core and a muddy mantle (ice with silicate impurities). In both cases, the crust is composed of a mixture of ice and silicates. These structures are constrained by a recent measurement of the mean density by Park et al. The Rayleigh-Taylor instability, which operates in such an unstable structure, could reverse all or part of the crust. The whole unstable crust (or part of it) can interact chemically with the underlying mantle and what is currently observed could be a partially/totally new crust. Our results suggest that, in the case of a pure ice mantle, the primordial crust has not survived until today, with a stability timespan always less than 3 Gyr. Conversely, in the case of a muddy mantle, with some `favourable' conditions (low volumetric ice percentage in the crust and small crustal thickness), the primordial crust could be characterized by a stability timespan compatible with the lifetime of the Solar system.

Although water vapour is the main species observed in the coma of comet 67P/Churyumov–Gerasimenko1, 2 and water is the major constituent of cometary nuclei3, 4, limited evidence for exposed water-ice regions on the surface of the nucleus has been found so far5, 6. The absence of large regions of exposed water ice seems a common finding on the surfaces of many of the comets observed so far7, 8, 9. The nucleus of 67P/Churyumov–Gerasimenko appears to be fairly uniformly coated with dark, dehydrated, refractory and organic-rich material10. Here we report the identification at infrared wavelengths of water ice on two debris falls in the Imhotep region of the nucleus. The ice has been exposed on the walls of elevated structures and at the base of the walls. A quantitative derivation of the abundance of ice in these regions indicates the presence of millimetre-sized pure water-ice grains, considerably larger than in all previous observations6, 7, 8, 9. Although micrometre-sized water-ice grains are the usual result of vapour recondensation in ice-free layers6, the occurrence of millimetre-sized grains of pure ice as observed in the Imhotep debris falls is best explained by grain growth by vapour diffusion in ice-rich layers, or by sintering. As a consequence of these processes, the nucleus can develop an extended and complex coating in which the outer dehydrated crust10 is superimposed on layers enriched in water ice. The stratigraphy observed on 67P/Churyumov–Gerasimenko11, 12 is therefore the result of evolutionary processes affecting the uppermost metres of the nucleus and does not necessarily require a global layering to have occurred at the time of the comet’s formation.

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.

Coalescing binary systems, consisting of two collapsed objects, are among the most promising sources of high frequency gravitational waves signals detectable, in principle, by ground-based interferometers. Binary systems of Neutron Star or Black Hole/Neutron Star mergers should also give rise to short Gamma Ray Bursts, a subclass of Gamma Ray Bursts. Short-hard-Gamma Ray Bursts might thus provide a powerful way to infer the merger rate of two-collapsed object binaries. Under the hypothesis that most short Gamma Ray Bursts originate from binaries of Neutron Star or Black Hole/Neutron Star mergers, we outline here the possibility to associate short Gamma Ray Bursts as electromagnetic counterpart of coalescing binary systems.

This article is in the 99th percentile (ranked 308th) of the 357,891 tracked articles of a similar age in all journals and the 94th percentile (ranked 54th) of the 934 tracked articles of a similar age in Nature. In the top 5% of all research outputs scored by Altmetric Studies of the dwarf planet (1) Ceres using ground-based and orbiting telescopes have concluded that its closest meteoritic analogues are the volatile-rich CI and CM carbonaceous chondrites. Water in clay minerals, ammoniated phyllosilicates, or a mixture of Mg(OH)2 (brucite), Mg2CO3 and iron-rich serpentine have all been proposed to exist on the surface. In particular, brucite has been suggested from analysis of the mid-infrared spectrum of Ceres. But the lack of spectral data across telluric absorption bands in the wavelength region 2.5 to 2.9 micrometres—where the OH stretching vibration and the H2O bending overtone are found—has precluded definitive identifications. In addition, water vapour around Ceres has recently been reported, possibly originating from localized sources. Here we report spectra of Ceres from 0.4 to 5 micrometres acquired at distances from ~82,000 to 4,300 kilometres from the surface. Our measurements indicate widespread ammoniated phyllosilicates across the surface, but no detectable water ice. Ammonia, accreted either as organic matter or as ice, may have reacted with phyllosilicates on Ceres during differentiation. This suggests that material from the outer Solar System was incorporated into Ceres, either during its formation at great heliocentric distance or by incorporation of material transported into the main asteroid belt.

Asteroid 21 Lutetia, visited by the Rosetta spacecraft, plays a crucial role in the reconstruction of primordial phases of planetary objects. Its high bulk density and its primitive chondritic crust (Weiss et al. 2011) suggest that Lutetia could be partially differentiated. We developed a numerical code, also used for studying the geophysical history of Vesta (Formisano et al., submitted), to explore several scenarios of internal evolution of Lutetia, differing in the strength of radiogenic sources and in the global post-sintering porosity. The only significant heat source for partial differentiation is represented by Al26, the other possible sources (Fe60, accretion and differentiation) being negligible. In scenarios in which Lutetia completed its accretion in less than 0.7 Ma from injection of Al26 in Solar Nebula and for post-sintering values of macroporosity not exceeding 30 vol. %, the asteroid experienced only partial differentiation. The formation of the proto-core, a structure enriched in metals and also containing pristine silicates, requires from 1 to 4 Ma: the size of the proto-core varies from 6 to 30 km., Comment: 12 pages, 2 tables, 4 figures. Accepted for publication on The Astrophysical Journal

Gravitational waves detected from well-localized inspiraling binaries would allow us to determine, directly and independently, binary luminosity and redshift. In this case, such systems could behave as "standard candles" providing an excellent probe of cosmic distances up to z, 4 pages, 2 figures and 2 tables. To appear in the Proceeding of the Spanish Relativity Meeting 2011 (Madrid, Spain, 29th August - 2nd September 2011)

Dynamics and collapse of collisionless self-gravitating systems is described by the coupled collisionless Boltzmann and Poisson equations derived from $f(R)$-gravity in the weak field approximation. Specifically, we describe a system at equilibrium by a time-independent distribution function $f_0(x,v)$ and two potentials $\Phi_0(x)$ and $\Psi_0(x)$ solutions of the modified Poisson and collisionless Boltzmann equations. Considering a small perturbation from the equilibrium and linearizing the field equations, it can be obtained a dispersion relation. A dispersion equation is achieved for neutral dust-particle systems where a generalized Jeans wave-number is obtained. This analysis gives rise to unstable modes not present in the standard Jeans analysis (derived assuming Newtonian gravity as weak filed limit of $f(R)=R$). In this perspective, we discuss several self-gravitating astrophysical systems whose dynamics could be fully addressed in the framework of $f(R)$-gravity., Comment: 8 pages, 2 figures, Accepted for publication in PRD

Gravitational waves detected from well-localized inspiraling binaries would allow to determine, directly and independently, both binary luminosity and redshift. In this case, such systems could behave as "standard candles" providing an excellent probe of cosmic distances up to $z, 6 pages, 5 figures. accepted in Astroparticle Physics

We discuss the possibility to obtain an electromagnetic emission accompanying the gravitational waves emitted in the coalescence of a compact binary system. Motivated by the existence of black hole configurations with open magnetic field lines along the rotation axis, we consider a magnetic dipole in the system, the evolution of which leads to (i) electromagnetic radiation, and (ii) a contribution to the gravitational radiation, the luminosity of both being evaluated. Starting from the observations on magnetars, we impose upper limits for both the electromagnetic emission and the contribution of the magnetic dipole to the gravitational wave emission. Adopting this model for the evolution of neutron star binaries leading to short gamma ray bursts, we compare the correction originated by the electromagnetic field to the gravitational waves emission, finding that they are comparable for particular values of the magnetic field and of the orbital radius of the binary system. Finally we calculate the electromagnetic and gravitational wave energy outputs which result comparable for some values of magnetic field and radius., 9 pages, 3 figures, to appear in Astroph. Sp.Science