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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

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.

1 – Introduction The early dynamical evolution of the Solar System is nowadays clear to be likely occurred in an non isolated context, like many studies of Sun evolution inside an Open Cluster suggest (see Pfalzner, 2015 for istance). Such a framework indicates us that even protoplanetary matter around young stars may evolve in complex environments, which is further proved by some recent observations of protoplanetary disks around stars in Open Clusters (Mann et al., 2015). An important role in the evolution of a disk in a non isolated system may be played by secular perturbations due to the far field stars, and, on the other hand, by the strong perturbations induced, on a shorter time-scale, by the close fly-bys. Occasional encounters with passing-by stars may considerably affect the dynamical evolution of the gas and change the balance of distribution of matter around each star. We aim to investigate such a framework by means of 3D numerical hydrodynamical simulations, schematizing a solar-like star+disk system perturbed by close encountering stars. By means of a Lagrangian Smoothed Particles Hydrodynamics (SPH) scheme, we calculate the evolution of the gas by including also the thermal effects induced by both the propagation of the radiation through the optically thick disk and the effects of the radiation coming from the stars. The temperature profile of a disk, which is substantially dependent on the thermal scheme assumed, may determine the turbulent viscous evolution of the disk itself and its susceptibility to the strong macroscopical perturbations induced by fly-by events. 2 – gas mixing and gas migration It is worth to consider some recent formation models according which the time scale of giant planet formation inside the disks may be less than 105 yr (Magni & Coradini, 2004; Brennecka et al., 2020), far shorter than the previous classical results which amount of the order of 106 yr . Such a framework changes considerably the action of the cluster in altering the disk evolution. As a matter of fact, on one hand, the role of far field star becames less prominent in influencing the destiny of a gaseous disk since the secular perturbations has a small interval of time to act. On the other hand, the early stages of an Open Cluster are typically characterized by a chaotic non-relaxed state, in which the close interactions have a substantially high probability to occur. Thus, if the key processes inside the disk happen in a relatively short time, the disks itself have good chances to undergo strong perturbations by close approaching stars during its crucial evolutionary phases close to the planet formation stage. We are interested to investigate two peculiar phenomena connected to the transport of matter induced by fly-by perturbation. One is represented by the macroscopical transport of matter from the inner to the outer layers of the disk, which may explain a still opened question about the Solar System consisting in unexpected observation of crystalline sylicates in comets (Brownlee et al. 2006). Despite sylicate compounds in comets are expected to be amorphous, they present a crystalline structure which need to be generated in the hot inner regions, hence incompatible with the current cometary distances from the sun. On the other hand, we focus our attention to gas swapping among stars consisting in substantial capture and migration of matter towards another star during a close encounter. The simplest case that may happen is characterized by a star, previously lacking of any gas distribution around, that acquires a new disk. But a rather more complex situation occurs when gas migrates towards another disk during its phases of gaseous planet formation, altering the planetary cores feeding process. The figure 1 shows an interesting example of gas migrated and captured by an approaching star, the sequence illustrates the main phases of truncation of a protoplanetary revolving around a single solar-like star, and further formation of a secondary tiny disk around the second star. 3 – Numerical method We implemented an SPH based code to integrate the hydrodynamical evolution of disks, with a tree code based algorithm to account for their selfgravity. SPH algorithms represent a class of lagrangian schemes commonly employed to face a wide range of astronomical problems ( see for example Monaghan, 2005 or Price & Monaghan, 2007) involving self-grativating fluids. They employ a set of free moving particles which automatically mimic the gas density distribution into the 3D space without the need of any regular mesh-grid. This is an essential feature in problems where rather irregular distributions of gas are involved, like our investigation where the close interactions between 2 or more stars and a disk may substantially alter the original morphology of the disks and cause violent matter migration. To perform the work, we developed an SPH algorithm (Pinto et al., 2019) to which we further added a radiative transfer scheme (according to the schematization of Viau et al., 2006) implemented with a careful study of the boundary conditions, due to the complex geometry and thermal exchange during a close encounter star–disk. This approach allows to describe a physically reasonable propagation of radiation through matter. References: - Brennecka et al. 2020, Science 370, 837–840 - Brownlee, D. et al. 2006, Science 314 , 1711 DOI: 10.1126/science.1135840 - Mann, R. K., Andrews, S. M., Eisner, J. A., et al. 2015, ApJ, 802, 77 - Magni, G. and Coradini, A. 2004, Planetary and Space Science 52, 343 - Monaghan, J. J. 2005, Reports on Progress in Physics, 68:1703–1759 - Pfalzner, S., Davies, M. B., Gounelle, M., et al. 2015, Physica Scripta, 90, 068001 - Price, D. J. and Monaghan, J. J. 2007, MNRAS, 374:1347–1358 - Pinto, L. D., Capuzzo-Dolcetta, R., and Magni, G. 2019, A&A 628, A82 - Viau, S. , Bastien, P. & Cha, S.H. 2006, ApJ, 639:559–570

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

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

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.

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.

The results of the in situ exploration of the asteroid (4) Vesta by the Dawn spacecraft open new perspectives in the field of interpretation of remote-sensing polarimetric measurements of asteroids. (4) Vesta has long been known to be the only asteroid exhibiting a cyclic variation of the degree of linear polarization of the sunlight scattered by its surface, with a period which is synchronous with the object's rotation. This variation must be the consequence of some heterogeneity of the asteroid's surface, including regions characterized by different albedo, or composition, or regolith properties, or a combination of the above features. For a long time, this kind of conclusion has remained essentially qualitative. Now, after the extensive exploration of Vesta's surface by Dawn, it is possible to interpret the data set of polarimetric measurements of Vesta, including some unpublished data presented here for the first time, in terms of a correspondence between the degree of linear polarization and the variation of local properties of the surface visible to ground-based observers during Vesta's rotation, as seen at different epochs and under different illumination conditions. This makes it possible to refine our knowledge of the empirical relation between polarization properties and albedo, which is commonly used to derive the albedo from remote-sensing measurements of linear polarization of atmosphereless Solar system bodies. Fil: Cellino, A.. Istituto Nazionale Di Astrofisica; Italia. Osservatorio Astrofisico di Torino; Italia Fil: Ammannito, E.. University of California at Los Angeles; Estados Unidos Fil: Magni, G.. Istituto Nazionale Di Astrofisica; Italia Fil: Gil Hutton, Ricardo Alfredo. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - San Juan. Complejo Astronómico "El Leoncito". Universidad Nacional de Córdoba. Complejo Astronómico "El Leoncito". Universidad Nacional de la Plata. Complejo Astronómico "El Leoncito". Universidad Nacional de San Juan. Complejo Astronómico "El Leoncito"; Argentina Fil: Tedesco, E. F.. Planetary Science Institute; Estados Unidos Fil: Belskaya, I. N.. Kharkiv National University. Institute of Astronomy; Ucrania Fil: De Sanctis, M. C.. Istituto Nazionale Di Astrofisica; Italia Fil: Schröder, S.. DLR Institute of Planetary Research; Alemania Fil: Preusker, F.. DLR Institute of Planetary Research; Alemania Fil: Manara, A.. Istituto Nazionale Di Astrofisica; Italia. Osservatorio Astronomico di Brera; Italia

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.

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

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

We present global lithological maps of the Vestan surface based on Dawn mission's Visible InfraRed (VIR) Spectrometer acquisitions with a spatial sampling of 200 m. The maps confirm the results obtained with the data set acquired by VIR with a spatial sampling of 700 m, that the reflectance spectra of Vesta's surface are dominated by pyroxene absorptions that can be interpreted within the context of the distribution of howardites, eucrites, and diogenites (HEDs). The maps also partially agree with the ground and Hubble Space Telescope observations: they confirm the background surface being an assemblage of howardite or polymict eucrite, as well as the location of a diogenitic-rich spot; however, there is no evidence of extended olivine-rich regions in the equatorial latitudes. Diogenite is revealed on the Rheasilvia basin floor, indicating that material of the lower crust/mantle was exposed. VIR also detected diogenites along the scarp of Matronalia Rupes, and the rims of Severina and a nearby, unnamed crater, and as ejecta of Antonia crater. The diogenite distribution is fully consistent with petrological constraints; although the mapped distribution does not provide unambiguous constraints, it favors the hypothesis of a magma ocean.

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

Dawn space mission will provide the first, detailed data of two of the major bodies in the main asteroid belt, Vesta and Ceres. Through its connection with Howardite, Eucrite, Diogenite (HED) meteorites, Vesta is known as one of the first bodies to have accreted and differentiated in the solar nebula, predating the formation of Jupiter and surviving the violent evolution of the early Solar system. The formation time of Ceres instead is unknown, but it should not postdate that of Jupiter by far, since the perturbations of the giant planet stopped planetary accretion in the main asteroid belt. In this work we modelled the collisional histories of Vesta and Ceres at the time of the formation of Jupiter, assumed to be the first giant planet to form. In this first investigation of the evolution of the early Solar system, we did not include the presence of planetary embryos in the disc of planetesimals but concentrated on the role of the forming Jupiter and the effects of its possible inward migration due to disc-planet interactions. Our results clearly indicate that the formation of the giant planet caused an intense early bombardment in the orbital region of the main asteroid belt. We explored the effects of such bombardment on Vesta and Ceres assuming different size distributions of the primordial planetesimals. According to our results, Vesta and Ceres would not have survived the Jovian early bombardment if the disc was populated mainly by large planetesimals like those predicted to form in turbulent circumstellar discs. Discs dominated by small bodies, like those predicted to form in quiescent circumstellar discs, or with a varying fraction of the mass in the form of larger (D ≥ 100 km) planetesimals, represent more favourable environments for the survival of the two asteroids. The abundance of planetesimals, especially the larger ones, proved a critical factor in this regard. The extent of Jupiter's radial migration due to disc-planet interactions proved itself another critical factor. In those scenarios where they survive, both asteroids had their surfaces saturated by craters as big as 150 km and a few as big as 200-300 km. In the case of Vesta, the Jovian early bombardment would have significantly eroded (locally or globally) the crust and possibly caused effusive phenomena similar to the lunar maria, whose crystallization time would then be directly linked to the time of the formation of Jupiter.

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

This work is dedicated to the application to 67P/Churyumov-Gerasimenko of a new quasi-3D approach for non-spherically shaped comet nuclei with the aim to interpret the current activity of the comet in terms of initial characteristics and to predict shape and internal stratification evolution of the nucleus. The model is applied to differently shaped nuclei taking into account the characteristics of Comet 67P/Churyumov-Gerasimenko deduced from observations. We focus our attention on the combined effects that shapes and obliquity have on the comet surface and sub-surface evolution. We discuss the results in terms of activity, local dust mantle formation and disruption, erosion of the surface and internal stratigraphy. The results show that differently shaped nuclei can have different internal structures leading to different activity patterns and behaviors. Our calculations have shown that local variations in the dust and gas fluxes can be induced by the nucleus shape. The distribution of “active” areas on Comet 67P/Churyumov-Gerasimenko is different because of different shapes, reflecting the illumination conditions on the surface. These shapes can influence the structure of the inner coma, but the coma far away from the nucleus is only marginally affected by the nucleus shape. However, different comet behaviors can arise from differently shaped comet nuclei, especially in terms of local activity, surface and sub-surface characteristics and properties. The water flux local distribution is the most influenced by the shape as it is directly linked to the illumination. Irregular shapes have large shadowing effects that can result in activity patterns on the comet surface. The effects of different pole directions are discussed to see the relations with the nucleus activity and internal structure. It is shown that the orientation of the rotation axis plays a strong role on the surface evolution of 67P/Churyumov-Gerasimenko, determining seasonal effects on the fluxes. The activity of the comet changes greatly with the nucleus obliquity leading to pre–post-perihelion differences in the activity and seasonal effects. The effects of the dust deposition and crust formation on the cometary activity have also been simulated and are discussed with respect to 67P/Churyumov-Gerasimenko observations. The dust mantling is also strongly obliquity dependent, with different surface distributions of the dust-covered regions according to the different comet pole orientations. Finally, we show that our model can reproduce the fluxes behavior near perihelion in terms of amplitude and asymmetry, and we estimate 20% of the illuminated surface to be active.

Dawn space mission will provide the first, detailed data of two of the major bodies in the Main Belt, Vesta and Ceres, and will allow us to study in depth the crater record on the surface of these asteroids and get an insight on their place in the context of Solar System history. In the framework of our studies on the origin of Solar System, we modelled the accretion of Jupiter and, through an N-Body code developed on purpose, we evaluated the flux of impactors on Vesta and Ceres keeping track of their formation zones. We also studied the effects of the possible inward migration of Jupiter on the rate and the characteristics of the impacts. We here describe the different scenarios and their implications for the evolution of Solar System to provide a reference frame for future studies of Vesta's and Ceres' cratering histories.

Recently it has been shown that long-lasting self-gravitating protoplanets can arise from a gravitationally unstable protoplanetary gaseous disks (Mayer et al., 2002). We are convinced that these calculations are extremely important to explain the existence of large extrasolar planets. Here we adopted a different approach, using as a reference scenario, the nucleated instability. This process takes place when the nebular gas is collected by an already formed solid core. This paper describes a long lasting project that simulates the formation of giant planets implementing the gas accretion onto the core via a 3-D hydro-dynamical model, recently developed in its present version (Magni and Coradini, 2003). Here we describe the structure of the central planet, while in a further paper we will treat the disk formation where possibly satellites were formed. To study the planet structure and the gas surrounding it we have considered three main regions: the central planet, a turbulent accretion disk which surrounds it and an extended region from which the gas is collected. The strong interaction between the growing planet and the surrounding gas warms the gas, creating a “barrier” that tends to reduce the accretion rate. The planet's thermodynamic structure depends upon the mass accretion rate onto it. The gas also exchanges angular momentum with the central body. Particular attention in the model has been paid to the analysis of angular momentum distribution between the growing planet and the disk. This work shows that we can match Jupiter present angular momentum.

In the course of the selection of the scientific themes for the second and third L-class missions of the Cosmic Vision 2015-2025 program of the European Space Agency, the exploration of the ice giant planets Uranus and Neptune was defined "a timely milestone, fully appropriate for an L class mission". Among the proposed scientific themes, we presented the scientific case of exploring both planets and their satellites in the framework of a single L-class mission and proposed a mission scenario that could allow to achieve this result. In this work we present an updated and more complete discussion of the scientific rationale and of the mission concept for a comparative exploration of the ice giant planets Uranus and Neptune and of their satellite systems with twin spacecraft. The first goal of comparatively studying these two similar yet extremely different systems is to shed new light on the ancient past of the Solar System and on the processes that shaped its formation and evolution. This, in turn, would reveal whether the Solar System and the very diverse extrasolar systems discovered so far all share a common origin or if different environments and mechanisms were responsible for their formation. A space mission to the ice giants would also open up the possibility to use Uranus and Neptune as templates in the study of one of the most abundant type of extrasolar planets in the galaxy. Finally, such a mission would allow a detailed study of the interplanetary and gravitational environments at a range of distances from the Sun poorly covered by direct exploration, improving the constraints on the fundamental theories of gravitation and on the behaviour of the solar wind and the interplanetary magnetic field., Comment: 29 pages, 4 figures; accepted for publication on the special issue "The outer Solar System X" of the journal Planetary and Space Science. This article presents an updated and expanded discussion of the white paper "The ODINUS Mission Concept" (arXiv:1402.2472) submitted in response to the ESA call for ideas for the scientific themes of the future L2 and L3 space missions

The Dawn spacecraft mission has provided extensive new and detailed data on Vesta that confirm and strengthen the Vesta-howardite-eucrite-diogenite (HED) meteorite link and the concept that Vesta is differentiated, as derived from earlier telescopic observations. Here, we present results derived by newly calibrated spectra of Vesta. The comparison between data from the Dawn imaging spectrometer—VIR—and the different class of HED meteorites shows that average spectrum of Vesta resembles howardite spectra. Nevertheless, the Vesta spectra at high spatial resolution reveal variations in the distribution of HED-like mineralogies on the asteroid. The data have been used to derive HED distribution on Vesta, reported in Ammannito et al. (2013), and to compute the average Vestan spectra of the different HED lithologies, reported here. The spectra indicate that, not only are all the different HED lithologies present on Vesta, but also carbonaceous chondritic material, which constitutes the most abundant inclusion type found in howardites, is widespread. However, the hydration feature used to identify carbonaceous chondrite material varies significantly on Vesta, revealing different band shapes. The characteristic of these hydration features cannot be explained solely by infalling of carbonaceous chondrite meteorites and other possible origins must be considered. The relative proportion of HEDs on Vesta's surface is computed, and results show that most of the vestan surface is compatible with eucrite-rich howardites and/or cumulate or polymict eucrites. A very small percentage of surface is covered by diogenite, and basaltic eucrite terrains are relatively few compared with the abundance of basaltic eucrites in the HED suite. The largest abundance of diogenitic material is found in the Rheasilvia region, a deep basin, where it clearly occurs below a basaltic upper crust. However, diogenite is also found elsewhere; although the depth to diogenite is consistent with one magma ocean model, its lateral extent is not well constrained.

The paper reviews the problem of formation and evolution of the so-called “regular satellites “ of the giant planets, and it consists of two parts: the first describes the possible origin of the satellites, the second studies their evolution, attempting to stress the relations of the present status of the satellites with their evolutionary history. The formation of regular satellite systems around giant planets is probably related to the formation of the central planet. Some characteristics of regular satellite systems are quite similar, and suggest a common origin in a disk present around the central body. This disk can originate through different mechanisms which we will describe, paying attention to the so-called “accretion disk” model, in which the satellite-forming material is captured. The disk phase links the formation of the primary body with the formation of satellites. The subsequent stages of the disk's evolution can lead first to the formation of intermediate size bodies, and through the collisional evolution of these bodies, to the birth of satellite “embryos” able to gravitationally capture smaller bodies. Given the scenario in which icy satellites may be formed by homogeneous accretion of planetesimals made of a mixtures of ice and silicates, if no melting occurs during accretion, the satellites have a homogeneous ice-rock composition. For the smaller satellites this homogeneous structure should not be substantially modified; only sporadic local events, such as large impacts, can modify the surface structure of the smaller satellites. For the larger satellites, if some degree of melting appears during accretion, a differentiation of the silicate part occurs, the amount of differentiation and hence the core size depending on the fraction of gravitational potential energy retained during the accumulation process. Melting and differentiation soon after the accretion, for the larger satellites, could also depend on the convective evolution in presence of phase transitions and generate an intermediate rock layer, considerably denser than the underlying, still homogeneous core, and unstable to overturning on a geologic time scale. Moreover the liquid water mantle could be a transient feature because the mantle would freeze over several hundred million years. For these large bodies the stable configuration is expected to be one consisting of a silicate core and a mantle of mixed rock and ice.

A New Dawn Since 17 July 2011, NASA's spacecraft Dawn has been orbiting the asteroid Vesta—the second most massive and the third largest asteroid in the solar system (see the cover). Russell et al. (p. 684 ) use Dawn's observations to confirm that Vesta is a small differentiated planetary body with an inner core, and represents a surviving proto-planet from the earliest epoch of solar system formation; Vesta is also confirmed as the source of the howardite-eucrite-diogenite (HED) meteorites. Jaumann et al. (p. 687 ) report on the asteroid's overall geometry and topography, based on global surface mapping. Vesta's surface is dominated by numerous impact craters and large troughs around the equatorial region. Marchi et al. (p. 690 ) report on Vesta's complex cratering history and constrain the age of some of its major regions based on crater counts. Schenk et al. (p. 694 ) describe two giant impact basins located at the asteroid's south pole. Both basins are young and excavated enough amounts of material to form the Vestoids—a group of asteroids with a composition similar to that of Vesta—and HED meteorites. De Sanctis et al. (p. 697 ) present the mineralogical characterization of Vesta, based on data obtained by Dawn's visual and infrared spectrometer, revealing that this asteroid underwent a complex magmatic evolution that led to a differentiated crust and mantle. The global color variations detailed by Reddy et al. (p. 700 ) are unlike those of any other asteroid observed so far and are also indicative of a preserved, differentiated proto-planet.

The Visible, InfraRed, and Thermal Imaging Spectrometer (VIRTIS) on Rosetta obtained hyperspectral images, spectral reflectance maps, and temperature maps of the asteroid 21 Lutetia. No absorption features, of either silicates or hydrated minerals, have been detected across the observed area in the spectral range from 0.4 to 3.5 micrometers. The surface temperature reaches a maximum value of 245 kelvin and correlates well with topographic features. The thermal inertia is in the range from 20 to 30 joules meter(-2) kelvin(-1) second(-0.5), comparable to a lunarlike powdery regolith. Spectral signatures of surface alteration, resulting from space weathering, seem to be missing. Lutetia is likely a remnant of the primordial planetesimal population, unaltered by differentiation processes and composed of chondritic materials of enstatitic or carbonaceous origin, dominated by iron-poor minerals that have not suffered aqueous alteration.

International audience; The Rosetta spacecraft accomplished a flyby of Mars on its way to 67P/Churyumov-Gerasimenko on 25 February 2007. In this paper we describe the measurements obtained by the M channel of the Visual and Infrared Thermal Imaging Spectrometer (VIRTIS-M) and the first scientific results derived from their analysis. The broad spectral coverage of the VIRTIS-M in the IR permitted the study of various phenomena occurring in the Martian atmosphere; observations were further exploited to achieve accurate absolute radiometric calibration. Nighttime data from the VIRTIS-M constrain the air temperature profile in the lower atmosphere (5-30 km), using variations in CO2 opacity at 4.3 mum. A comparison of this data with the global circulation model (GCM) by Forget et al. (1999) shows a trend of slightly higher air temperature in the VIRTIS-M retrievals; this is accompanied by the presence of moderate decreases (˜5 K) in large sections of the equatorial region. This is potentially related to the occurrence of water ice clouds. Daytime data from the VIRTIS-M reveal CO2 non-local thermodynamic equilibrium emission in the high atmosphere. A mapping of emission intensity confirms its strict dependence on solar zenith angle. Additionally, devoted limb observations allowed the retrieval of vertical emission intensity profiles, indicating a peak around 105 km in southern tropical regions. Ozone content can be effectively monitored by the emission of O2 (a1Deltag) at 1.27 mum. Retrieved emission intensity shows that polar regions are particularly rich in ozone. Aerosol scattering was observed in the 1-2.5 mum region above the night region above the night disk, suggesting the occurrence of very high noctilucent clouds.

The formation of regular satellite systems around outer planets is discussed here, with particular attention to the so called disk phase, which links the formation of the primary body to that of the satellites. Disk models are proposed for Jupiter, Saturn and Uranus disks. The subsequent evolutive phases leading to the present satellite masses (formation of local planetesimals, collisional evolution leading to the formation of satellite embryos, and final accretion) are discussed as well and summarized.

The targets of the Rosetta mission are the most primitive solar system bodies: comets and asteroids. The previous Rosetta mission was essentially devoted to study in detail a comet nucleus and to fly by one or two asteroids. The new mission Rosetta is set to rendezvous with Comet 67P/Churyumov — Gerasimenko, orbiting around it and making observations as it journeys towards the Sun. En route to the comet it will flyby at least one asteroid. The study of small bodies is crucial to understand the solar system formation. In fact it is believed that comets and, to a lesser extent, asteroids underwent a moderate evolution so that they preserve some pristine solar system material. The scientific payload of Rosetta includes a Visual InfraRed Thermal Imaging Spectrometer (VIRTIS) among the instruments on board the spacecraft orbiting around the comet. This instrument is fundamental to detect and study the evolution of specific fingerprints — such as the typical spectral bands of minerals and molecules — arising from surface components and from materials dispersed in the coma. Their identification is a primary goal of the Rosetta mission as it will allow us to identify the nature of the main constituents of the comets. Moreover, the surface thermal evolution during comet approach to Sun will provide essential information on the thermal and structural evolution of the comet nucleus. VIRTIS data will permit to identify as well the chemical evolution of the surface. The VIRTIS design and its detailed science goals will be discussed, as well as the new observation strategy and the on-ground calibrations.

IPSE is a scientific autonomous micro-laboratory for Mars soil and environment analysis. It is designed to provide the capability to serve, handle and manage scientific miniaturised instruments accommodated inside its envelope. These instruments will carry out measurements on soil samples, atmosphere, radiation environment and dust flux. IPSE is an example of a small and flexible laboratory, that can be integrated on different landers and rovers. It contains: scientific instruments; a small robotic arm to provide samples to the instruments; power conditioning; electronics for system and thermal control, communications and instrument data handling.

IPSE is a micro-laboratory for Mars soil and environment analysis. It provides the capability to serve and handle scientific miniaturised instruments accommodated inside its envelope. The instruments have the goal to perform in situ study of the collected martian samples, thus quantitatively characterizing the mineralogy, the composition, the microphysical structure of the materials of the Martian soils down to the depth available to the sampling mechanism. Given the complex structure of the surface material it will be essential to perform in-situ science, both at the surface and at different depths. This is done in order to validate remote sensing observations through specific measurements, identify local characteristics of the selected landing areas, document sample collection both for in situ and sample return. IPSE is an example of a small and flexible lab, that can be integrated on different Landers and Megarovers. IPSE contains: • Scientific instruments • A small robotic arm - with five degrees of freedom - to provide samples to the IPSE instruments. • Power conditioning. • Electronics for system and thermal control, communications and instrument data handling. The Phase A report for all the IPSE instruments has been already provided to the Italian Space Agency. The experiments MAGO, IRMA, MA_FLUX are inherited from previous space qualified instruments and breadboards of them already exist. DOSE is a new experiment, however, a breadboard of the detector and of the photomultiplier is under development.

The visible infrared thermal imaging spectrometer (VIRTIS) is one of the principal payloads to be launched in 2003 on ESA's Rosetta spacecraft. Its primary scientific objective s are to map the surface of the comet Wirtanen, monitor its temperature, and identify the solids and gaseous species on the nucleus and in the coma. VIRTIS will also collet data on two asteroids, one of which has been identified as Mimistrobell. The data is collected remotely using a mapping spectrometer co-boresighted with a high spectral resolution spectrometer. The mapper consists of a Shafer telescope matched to an Offner grating spectrometer capable of gathering high spatial, medium spectral resolution image cubes in the 0.25 to 5 micrometers waveband. The high spectral resolution spectrometer uses an echelle grating and a cross dispersing prism to achieve resolving powers of 1200 to 300 in the 1.9 to 5 micrometers band. Both sub-systems are passively cooled to 130 K and use two Sterling cycle coolers to enable two HgCdTe detector arrays to operate at 70 K. The mapper also uses a silicon back-side illuminated detector array to cover the ultra-violet to near-infrared optical band.© (1996) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

The baseline model payload of Rosetta includes a visual infrared spectral and thermal mapper among the instruments on board the spacecraft orbiting around the comet. This instrument will allow the following scientific goals to be achieved: to characterise the nucleus surface composition (concentration of the ices, mineralogical composition of dust, characteristics of organic compounds); to determine the surface temperature distribution and the dust and gas distribution in the inner cometary coma; to map the asteroid's surface mineralogical composition. In order to achieve these scientific objectives the authors are projecting an instrument composed of two channels: an imaging spectrometer (VIRTIS-M, where M means Mapping mode) and a high resolution spectrometer (VIRTIS-H).

Water plays a key role in the evolution of terrestrial planets, and notably in the occurrence of Earth's oceans. However, the mechanism by which water has been incorporated into these bodies—including Earth—is still extensively debated. Here we report the detection of widespread 2.8 μm OH absorption bands on the surface of the asteroid Vesta by the VIR imaging spectrometer on board Dawn. These observations are surprising as Vesta is fully differentiated with a basaltic surface. The 2.8 μm OH absorption is distributed across Vesta's surface and shows areas enriched and depleted in hydrated materials. The uneven distribution of hydrated mineral phases is unexpected and indicates ancient processes that differ from those believed to be responsible for OH on other airless bodies, like the Moon. The origin of Vestan OH provides new insight into the delivery of hydrous materials in the main belt and may offer new scenarios on the delivery of hydrous minerals in the inner solar system, suggesting processes that may have played a role in the formation of terrestrial planets.

It is shown that by means of elementary assumptions it is possible to obtain models of planetary systems not too different from the observed case. Such assumptions are shown to be the bulk of more detailed models as those by Dole (1970) and Isaacman and Sagan (1977).