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Abstract: The flyby of the Main Belt asteroid Lutetia by the Rosetta spacecraft allows the camera OSIRIS to obtain very good images of about half of the body at the maximum resolution of 60m per pixel. From the images and radio-science experiment, a density of about (3.4±0.3)g/cm3 has been inferred for the asteroid. Many impact craters have been observed on the surface of Lutetia and the largest, named Massilia, has a diameter of about 55km. Relative to the size of Lutetia (the longest axis is approximately 126km) the crater represents one of the dominating features on its surface. Whether or not the impact that formed Massilia affected the entire asteroid can be only evaluated via numerical modeling, with hydrocodes, of the impact process. The results of a suite of iSALE simulations are compared with the crater profile derived from the Digital Terrain Model of the observed surface. The best match to the DTM of the crater with hydrocode simulations has allowed to determine a value of 7.5km for the impactor diameter, which suggests a primordial origin of Lutetia due to the low probability of such an impact event. A second interesting impact structure has been identified nearby Massilia within the North Pole Crater Cluster. The crater has a diameter of 24km and it lies over a larger crater of the North Pole Crater Cluster. This is strongly suggestive of a very young structure on Lutetia. The numerical simulations of this feature constrain the impactor to be 3.8km in diameter, assuming the same material properties for target and impactor as in the model of the formation of Massilia. [Copyright &y& Elsevier]

Abstract: Modern telescopes and equipments have permitted excellent ground-based observations of Mercury, despite its proximity to the Sun. This is one of the main reasons why it has been observed using different techniques from high-resolution spectroscopy to high-resolution imaging from visible to infrared up to radio wavelengths. Because there is no obscuration from a thick atmosphere, the surface and exosphere have been imaged and the surface studied by infrared spectroscopy. This manuscript describes the techniques used to obtain information and new data of Mercury giving an overview of advantages and difficulties, and describes important scientific discoveries made with specific telescopic instrumentation. [Copyright &y& Elsevier]

Abstract: In this work, we calculate the neutral Na production rates on the Moon and Mercury, as due to the impacts of meteoroids having an impact probability on the surface that can influence the daily observations of the exosphere: the meteoroids radius range considered for the Moon and Mercury are 10−8–0.15 and 10−8–0.10m, respectively. We also estimate the mass of meteoroids that has impacted the surfaces of the Moon and Mercury in the last 3.8Gy (after the end of the Late Heavy Bombardment). The results of our model are that (i) the Na production rates are ∼(3–4.9)×104 and ∼(1.8–2.3)×106 atoms cm−2 s−1, for Moon and Mercury, respectively, and (ii) in the last 3.8Gy, the mass of meteoroids that has impacted the whole surface of the Moon and Mercury has been 8.86×1018 and 2.66×1019 g, respectively. [Copyright &y& Elsevier]

The composition of comets hold clues about the early stages of the formation and evolution of the Solar System. Being the brightest comet observed in the northern hemisphere since the passage of comet C/1995 O1 (Hale-Bopp) in 1997, comet C/2020 F3 (NEOWISE) represents an interesting target for studying its coma composition and the chemical inventory of its nucleus. We aim to estimate the production rate (mol/s) for the chemical species identified in the coma. By comparing with other comets, we aim to assess whether this comet is typical or peculiar, and investigate any distinctive feature. From high resolution (R ​= ​115000) spectra of C/2020 F3 at 0.72 AU from the Sun obtained with the HARPS-N instrument at the TNG, we measured the flux of selected C 2 , CN, C 3 , NH 3 and O(1D) bands and emission lines, that were converted to production rates (Q) through the Haser formalism. From O(1D) we derive the production rate of water molecules. These values are then normalized with respect to CN and water production rates and compared with results from other spectroscopic surveys. We estimate production rates Q (CN) = (1.55 ​± ​0.39) ⋅ 1026 ​mol/s, Q (C 2) = (1.76 ​± ​0.32) ⋅ 1026 ​mol/s, Q (C 3) = (0.32 ​± ​0.12) ⋅ 1026, Q (H 2 O) = (3481.32 ​± ​3.48) ⋅ 1026 ​mol/s and Q (NH 2) = (10.58 ​± ​3.64) ⋅ 1026 ​mol/s. With respect to water, we find relatively lower (by a factor of ≈ 4 − 5) CN and C 2 mixing ratios and a relatively high NH 2 mixing ratios than other comets, especially for heliocentric distances below 1 AU. The calculated production rates and their ratios highlight discrepancies in the sublimation of comet C/2020 F3 with respect to Solar System comets and are consistent with the presence of a nucleus with a heterogeneous composition, already proposed in literature. • We estimate production rates of C2, CN, C3 NH2 and water for comet C/2020 F2 (NEOWISE) at 0.72 AU through high-resolution spectroscopy and Haser modelling • We find significantly higher NH2based and water ice sublimation with respect to a sample of Solar System comets • We find significant depletion in C-based ices • We suggest that the cometary activity of C/2020 F3 can be explained by a nucleus of heterogeneous composition [ABSTRACT FROM AUTHOR]

The great amount of data that will be produced during the imaging of Mercury by the stereo camera (STC) of the BepiColombo mission needs a compromise with the restrictions imposed by the band downlink that could drastically reduce the duration and frequency of the observations. The implementation of an on-board real time data compression strategy preserving as much information as possible is therefore mandatory. The degradation that image compression might cause to the DTM accuracy is worth to be investigated. During the stereo-validation procedure of the innovative STC imaging system, several image pairs of an anorthosite sample and a modelled piece of concrete have been acquired under different illumination angles. This set of images has been used to test the effects of the compression algorithm ( Langevin and Forni, 2000 ) on the accuracy of the DTM produced by dense image matching. Different configurations taking in account at the same time both the illumination of the surface and the compression ratio, have been considered. The accuracy of the DTMs is evaluated by comparison with a high resolution laser-scan acquisition of the same targets. The error assessment includes also an analysis on the image plane indicating the influence of the compression procedure on the image measurements. [ABSTRACT FROM AUTHOR]

Abstract: In this paper we present a crater age determination of several terrains associated with the Raditladi and Rachmaninoff basins. These basins were discovered during the first and third MESSENGER flybys of Mercury, respectively. One of the most interesting features of both basins is their relatively fresh appearance. The young age of both basins is confirmed by our analysis on the basis of age determination via crater chronology. The derived Rachmaninoff and Raditladi basin model ages are about 3.6Ga and 1.1Ga, respectively. Moreover, we also constrain the age of the smooth plains within the basins'' floors. This analysis shows that Mercury had volcanic activity until recent time, possibly to about 1Ga or less. We find that some of the crater size-frequency distributions investigated suggest the presence of a layered target. Therefore, within this work we address the importance of considering terrain parameters, as geo-mechanical properties and layering, into the process of age determination. We also comment on the likelihood of the availability of impactors able to form basins with the sizes of Rachmaninoff and Raditladi in relatively recent times. [Copyright &y& Elsevier]

Abstract: The BepiColombo space mission is one of the European Space Agency''s cornerstone projects; it is planned for launch in 2013 to study the planet Mercury. One of the imaging instruments of BepiColombo is a STereo Camera (STC), whose main scientific objective is the global stereo mapping of the entire surface of Mercury. STC will permit the generation of a Digital Terrain Model (DTM) of Mercury''s surface, improving the interpretation of morphological features at different scales and clarifying the stratigraphic relationships between different geological units. To evaluate the effectiveness of the STC-derived DTM for geological purposes, a series of simulations has been performed to find out to what extent the errors expected in the DTM may prevent the correct classification and interpretation of geological features. To meet this objective, Earth analogues (a crater, a lava cone and an endogenous dome) of likely components of the Hermean surface, small enough to be near the detection limit of the STC, were selected and a photorealistic three-dimensional (3D) model of each feature was generated using Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) stereo images. Stereoscopic pairs of synthetic images of each feature were then generated from the 3D model at different locations along the BepiColombo orbit. For each stereo pair, the corresponding Hermean DTM was computed using image correlation and compared to the reference data to assess the loss of detail and interpretability. Results show that interpretation and quantitative analysis of simple craters morphologies and small volcanic features should be possible all along the periherm orbit arc. At the apoherm only the larger features can be unequivocally distinguished, but they will be reconstructed to a poor approximation. [Copyright &y& Elsevier]

Recurring Slope Lineae (RSL) are narrow, dark features that typically source from rocky outcrops, incrementally lengthen down Martian steep slopes in warm seasons, fade in cold seasons and recur annually. In this study we report the first observations of RSL at Hale crater, Mars, during late southern summer by the Color and Surface Science Imaging System (CaSSIS) on board ESA's ExoMars Trace Gas Orbiter (TGO). For the first time, we analyze images of RSL acquired during morning solar local times and compare them with High Resolution Imaging Science Experiment (HiRISE) observations taken in the afternoon. We find that RSL activity is correlated with the presence of steep slopes. Our thermal analysis establishes that local temperatures are high enough to allow either the melting of brines or deliquescence of salts during the observation period, but the slope and aspect distributions of RSL activity predicted by these processes are not consistent with our observations. We do not find any significant relative albedo difference between morning and afternoon RSL. Differences above 11% would have been detected by our methodology, if present. This instead suggests that RSL at Hale crater are not caused by seeping water that reaches the surface, but are best explained as dry flows of granular material. • We report the first CaSSIS observations of RSL at Hale crater, Mars. • We compare morning CaSSIS images with afternoon HiRISE observations. • We do not find any relative albedo variations between morning and afternoon RSL. • RSL lengthening is constrained to steep slopes. • Our results indicate that RSL are consistent with dry flows. [ABSTRACT FROM AUTHOR]

Abstract The previously defined regions on the nucleus of comet 67P/Churyumov-Gerasimenko have been mapped back onto the 3D SHAP7 model of the nucleus (Preusker et al., 2017). The resulting regional definition is therefore self-consistent with boundaries that are well defined in 3 dimensions. The facets belonging to each region are provided as supplementary material. The shape model has then been used to assess inhomogeneity of nucleus surface morphology within individual regions. Several regions show diverse morphology. We propose sub-division of these regions into clearly identifiable units (sub-regions) and a comprehensive table is provided. The surface areas of each sub-region have been computed and statistics based on grouping of unit types are provided. The roughness of each region is also provided in a quantitative manner using a technique derived from computer graphics applications. The quantitative method supports the sub-region definition by showing that differences between sub-regions can be numerically justified. Highlights • Regions are defined upon the latest 3D shape model (SHAP7) of comet 67P/Churyumov-Gerasimenko. • The definition is provided in a publicly accessible shape file. • Sub-regions of similar properties are defined to support more detailed work. • Roughness calculations are performed to quantify differences between regions and sub-regions. [ABSTRACT FROM AUTHOR]

CaSSIS is a high-resolution visual telescope onboard the ExoMars Trace Gas Orbiter. The mission started the primary science phase in April 2018. The relatively small single image footprint (typically 40 ​km ​× ​9.5 ​km) when compared to the total surface area of Mars demands that images should be targeted and target selection is key for the science return. This paper describes the science planning concept set around the target selection, and the process followed in order to generate the CaSSIS commands. The tools used are described as well as all the iterations and teams involved. Finally, special cases and the handling of contingencies are discussed. The procedures may serve as a guideline for future high-resolution instruments on missions to planetary objects. [Display omitted] • CaSSIS imaging. • Mars High Resolution Targeting tools. • Mars Features Database. • Planning processes and automation. [ABSTRACT FROM AUTHOR]

The ESA Rosetta spacecraft has been tracking its target, the Jupiter-family comet 67P/Churyumov-Gerasimenko, in close vicinity for over two years. It hosts the OSIRIS instruments: the Optical, Spectroscopic, and Infrared Remote Imaging System composed of two cameras, see e.g. Keller et al. (2007) . In some imaging sequences dedicated to observe dust particles in the comet's coma, the two cameras took images at the same time. The aim of this work is to use these simultaneous double camera observations to calculate the dust particles’ distance to the spacecraft. As the two cameras are mounted on the spacecraft with an offset of 70 cm, the distance of particles observed by both cameras can be determined by a shift of the particles’ apparent trails on the images. This paper presents first results of the ongoing work, introducing the distance determination method for the OSIRIS instrument and the analysis of an example particle. We note that this method works for particles in the range of about 500–6000 m from the spacecraft. [ABSTRACT FROM AUTHOR]

The Colour and Stereo Surface Science Imaging System (CaSSIS) of the ExoMars Trace Gas Orbiter returns on average twenty images per day of the Martian surface, most of them in 3 or 4 colours and some of them in stereo. CaSSIS uses a push-frame approach to acquire colour images, with four bandpass filters deposited directly above the sensor and an imaging cadence synchronized with the ground track velocity to cover the imaged area with tens of small, partially overlapping images. These "framelets" are later map-projected and mosaicked to build the final image. This approach offers both advantages and challenges in terms of radiometric calibration. While the collection of dark and flatfield frames is considerably enhanced by the frequent and fast acquisition of tens of successive images, mosaics assembled from the adjacent framelets highlight the straylight and changes in the bias of the detector. Both issues have been identified on CaSSIS images, with low intensities overall (up to a few %), but sufficient to generate prominent artefacts on the final assembled colour images. We have therefore developed methods to correct these artefacts that are now included into the radiometric calibration pipeline. We detail here the different steps of the calibration procedure and the generation of the products used for calibration, and discuss the efficacy of the corrections. The relative uncertainties on the bias and flatfield frames are low, of the order of 0.2 and 0.1%, respectively. The uncertainty on the absolute radiometric calibration is of 3%, which is quite low for such an instrument. The straylight adds an estimated ∼1% error to the absolute calibration. The residuals after corrections of the straylight and bias offsets are of the order of a few DNs to tens of DNs. As CaSSIS can observe the Martian surface in challenging illumination conditions to provide unique views of the surface at early and late local solar time, residuals from the straylight correction can become noticeable when the absolute signal is very low. As they appear at the level of the noise in very low illumination images, these residuals do not limit the scientific exploitation of the data. For most of the dataset, as the signal in well-exposed images reaches 8000 DNs in the panchromatic filter and thousands of DNs in the colour filters, the residuals are negligible and CaSSIS provides the best colour images available over many areas covered. [Display omitted] • Description of the radiometric calibration procedure for the CaSSIS imager of Exomars TGO. • High precision and stability of the calibration products bias and flatfield. • Correction of straylight and instabilities of the detector bias. • Discussion of uncertainties in the calibration and residuals vs. signal. [ABSTRACT FROM AUTHOR]

Planview detailed morphological analysis of martian landslides is usually performed using orbital imagery such as from the ConTeXt camera (CTX) at 6 ​m/pix, the Colour and Stereo Surface Imaging System (CaSSIS) at 4.5 ​m/pix or the High-Resolution Imaging Science Experiment (HiRISE) at 0.25–0.5 ​m/pix. However, topographic information is key to fully understand a landslide's formation mechanism and its mobility, by estimating the material volumes mobilised and the spatial distribution of erosion and deposition. Digital Elevation Models (DEM) are required to carry out these analyses; nevertheless, there is currently a gap in landslide-volume studies between those using Mars Orbiter Laser Altimeter (MOLA) dataset at ∼450 ​m/pix or HRSC at 50–200 m/pix and those using HiRISE data at 1–2 m/pix, which is only partially filled by CTX elevation data at ∼20 ​m/pix. The CaSSIS camera on board the ESA/Trace Gas Obiter (TGO) can be used to produce DEMs, but so far, such data have not yet been used to conduct a landslide volume analysis. Here, we use three reconstruction methods (semi-automatic, morphology-based and tilted) on a CaSSIS DEM to estimate the initial topography and hence the volume and the distribution of erosion and deposition of a 6 ​km long landslide in Baetis Chaos. Despite the complex topography of the surrounding area due to the presence of an ejecta deposit beneath the landslide, we were able to estimate the landslide's volume and mass distribution. Using a tilted plane as part of estimating the initial topography produced the best results. We evaluated the success by considering the quantifiable balance between erosion and deposition (given the uncertainties) and more subjectively by considering whether the volume distribution matched with what was expected based on the morphology in images alone. Therefore, we recommend the use of this method for individual landslide studies in complex topography where detailed knowledge of the deposit-thickness distribution is required. The semi-automatic reconstruction method produces satisfactory volume estimates and would be better suited to studies where hundreds of landslides are present. We found that CaSSIS data can be used to successfully conduct such analyses, providing additional DEM coverage to study martian medium-scale landslides or other landforms of similar scale (5–15 ​km) with the notable benefit that it provides single-pass stereo image acquisition. • Digital Elevation Model are needed to estimates landslide's material volumes and distribution in order to fully understand their mobility. • CaSSIS (Colour and Stereo Surface Imaging System) DEM have not yet been used to conduct such landslide analysis. • Three reconstruction on a CaSSIS DEM have been used to estimate the volume and the material distribution of a landslide in Baetis Chaos on Mars. • CaSSIS data can be used to conduct analysis and provide additional coverage to study medium-scale landslides or other landforms (scale 5–15 km). [ABSTRACT FROM AUTHOR]

Before reaching Jupiter and its icy moons, the ESA JUpiter ICy moons Explorer (JUICE) spacecraft will travel ∼8 years within the inner Solar System, entering the asteroid Main Belt (MB) twice. This is a unique opportunity to flyby and investigate at close range one or more asteroids, as previously done by other missions. In order to identify multiple asteroids as possible targets of opportunity for the JUICE cruise phase, we developed a new code, called Automatic Asteroid Search Toolkit (A 2 ST), which determines the minimum distance between the orbit of ∼140.000 asteroids and the spacecraft. From the list of potential objects ordered by range, we identify asteroid (1650) Heckmann and (223) Rosa as two objects of particular scientific interest. (1650) Heckmann is a ∼30 ​km-size inner MB member of the Polana asteroid family and it belongs to a taxonomical group (F-type) that has never been observed at close range. On the contrary (223) Rosa is an outer ∼80 ​km-size dark MB asteroid (X-type or T-type) whose origin is not yet fully understood. Indeed, it may be a collisional fragment of the Themis family or a primitive dark planetesimal that formed in the outer Solar System. The in-situ observation of both targets by the JUICE mission would widely expand the knowledge of the Solar System formation and evolution, as well as the compositional structure of the Main Belt, hence maximising the scientific return of the full mission. • Distance of about 140000 asteroids to JUICE spacecraft has been evaluated. • Image size of the asteroid diameter on JANUS camera has been evaluated. • A list of 71 potential targets of opportunity has been determined. • Two asteroids are proposed as potential close-range flyby for JUICE mission. [ABSTRACT FROM AUTHOR]

Recurring Slope Lineae (RSL) are narrow, dark streaks typically lengthening down Martian steep slopes during warm seasons, fading during the cold ones and regularly recurring every Martian year. Their origin is still debated. Although initially interpreted as possible flows of seeping water, either coming from a subsurface aquifer or through atmospheric processes, recent studies favor a dry granular flow origin. To date, the nature and formation mechanism of RSL represent an open science question about present-day surface processes occurring on Mars. In this study, we analyze color observations of RSL at Horowitz crater, acquired with the Colour and Surface Science Imaging System (CaSSIS) on board ESA's ExoMars Trace Gas Orbiter (TGO) mission. We compare the relative photometry of RSL with respect to nearby terrains with the relative reflectance of dust-removed surfaces, including dust-devil tracks, in the four CaSSIS filters to help assess their properties. Comparing our relative photometry with dust-deposition and soil-wetting models coming from published laboratory experiments, we find that the former results provide a better fit to the observations than the latter, hence supporting a dry origin for Horowitz RSL. [Display omitted] • Recurring Slope Lineae are martian surface feature which origin is still debated. • We present the first 4 band relative albedo measurements of RSL performed with CaSSIS data. • Our analysis support a dry origin for RSL. [ABSTRACT FROM AUTHOR]

Abstract: The surface of (21) Lutetia is highly complex with significant interactions between ancient and more recent structures. This work attempts to summarize the surface geomorphology observed using the high resolution images from OSIRIS, the imaging system onboard the European Space Agency''s Rosetta spacecraft. A wide range of surface morphologies are seen including heavily cratered terrain, extensive sets of lineaments, young impact craters, and a ridge, the height of which is more than 1/5th of the mean radius of the body. Very young and very old terrains (as inferred from crater densities) are seen in close proximity. The longest continuous lineament is over 80km long. The lineaments show regional-dependent organization and structure. Several categories of lineament can be described. Lineaments radial to impact craters as seen on other asteroidal bodies are mostly absent. Although the lineaments may be of seismic origin (and possibly the result of several impact-induced events), impacts producing recent large craters place constraints on seismic phenomena. In particular, stronger attenuation of shocks than seen on other asteroidal bodies seems to be required. Inhomogeneous energy transport, possibly matching observed inhomogeneous ejecta deposition may offer explanations for some of the observed phenomena. Some impact craters show unusual forms, which are probably the result of impact into a surface with relief comparable to the resultant crater diameter and/or oblique impact. There is evidence that re-surfacing through landslides has occurred at several places on the object. [Copyright &y& Elsevier]

Abstract: The cratering history of main belt asteroid (2867) Steins has been investigated using OSIRIS imagery acquired during the Rosetta flyby that took place on the 5th of September 2008. For this purpose, we applied current models describing the formation and evolution of main belt asteroids, that provide the rate and velocity distributions of impactors. These models coupled with appropriate crater scaling laws, allow the cratering history to be estimated. Hence, we derive Steins’ cratering retention age, namely the time lapsed since its formation or global surface reset. We also investigate the influence of various factors—like bulk structure and crater erasing—on the estimated age, which spans from a few hundred Myrs to more than 1Gyr, depending on the adopted scaling law and asteroid physical parameters. Moreover, a marked lack of craters smaller than about 0.6km has been found and interpreted as a result of a peculiar evolution of Steins cratering record, possibly related either to the formation of the 2.1km wide impact crater near the south pole or to YORP reshaping. [Copyright &y& Elsevier]

Abstract: The Mercury Sodium Atmosphere Spectral Imager (MSASI) on the Mercury Magnetospheric Orbiter (MMO) of the JAXA/ESA Bepi-Colombo (BC) Mission will address a range of fundamental scientific questions pertaining to Mercury''s exosphere. The measurements will provide new information on regolith–exosphere–magnetosphere coupling as well as new understanding of the dynamics governing the exosphere bounded by the planetary surface, the solar wind and interplanetary space. MSASI is a high-dispersion visible spectrometer working in the spectral region near the sodium D2 emission (589nm), a major constituent of the Mercury exosphere. A single high-resolution Fabry–Perot etalon is used in combination with a narrow-band interference filter to achieve a compact and efficient instrument design. The etalon and filter are extremely stable with respect to long-term aging and temperature variations. Full-disk images of the planet are obtained by means of a single-axis scanning mirror in combination with the spin of the MMO spacecraft. This paper presents an overview of the MSASI and the design of the Fabry–Perot interferometer used as its spectral analyser. It is concluded that: [(1)] The MSASI optical design is practical and can be implemented without new or critical technology developments. [(2)] The thermally stable etalon design is based on concepts, designs and materials that have a good space heritage. [(3)] The MSASI instrument will achieve a high signal-to-noise ratio (SNR) (>10) in the range of 2K–10M Rayleigh. [Copyright &y& Elsevier]

Abstract: The limited knowledge about the majority of the Mercury surface leaves many open questions regarding its geological evolution, the anomalously high metal/silicate ratio, the magnetic field generation and exosphere evolution. An integrated suite of instruments, Spectrometer and Imagers for MPO BepiColombo-Integrated Observatory SYStem (SIMBIO-SYS), which includes a stereo imaging system (STC), a high-resolution imager (HRIC) and a visible–near-infrared imaging spectrometer (VIHI), has been selected for the ESA BepiColombo mission to Mercury. SIMBIO-SYS will scan the hermean surface with the three channels and map the physical, morphological, tectonic and compositional properties of the entire planet. The availability of high-resolution images will unveil details of specific target at an unprecedented resolution. The main scientific objectives and performances along with technical characteristics of SIMBIO-SYS are described in this paper. [Copyright &y& Elsevier]

Abstract: Mercury possesses a weak, internal, global magnetic field that supports a small magnetosphere populated by charged particles originating from the solar wind, the planet''s exosphere and surface layers. Mercury''s exosphere is continuously refilled and eroded through a variety of chemical and physical processes acting in the planet''s surface and environment. Using simultaneous two-point measurements from two satellites, ESA''s future mission BepiColombo will offer an unprecedented opportunity to investigate magnetospheric and exospheric dynamics at Mercury as well as their interactions with solar radiation and interplanetary dust. The expected data will provide important insights into the evolution of a planet in close proximity of a star. Many payload instruments aboard the two spacecraft making up the mission will be completely, or partially, devoted to studying the close environment of the planet as well as the complex processes that govern it. Coordinated measurements by different onboard instruments will permit a wider range of scientific questions to be addressed than those that could be achieved by the individual instruments acting alone. Thus, an important feature of the BepiColombo mission is that simultaneous two-point measurements can be implemented at a location in space other than the Earth. These joint observations are of key importance because many phenomena in Mercury''s environment are temporarily and spatially varying. In the present paper, we focus on some of the exciting scientific goals achievable during the BepiColombo mission through making coordinated observations. [Copyright &y& Elsevier]

Abstract: Inflation is an emplacement process of lava flows, where a thin visco-elastic layer, produced at an early stage, is later inflated by an underlying fluid core. The core remains hot and fluid for extended period of time due to the thermal-shield effect of the surface visco-elastic crust. Plentiful and widespread morphological fingerprints of inflation like tumuli and lava rises are found on the Payen volcanic complex (Argentina), where pahoehoe lava flows extend over the relatively flat surface of the Pampean foreland and reach at least 180km in length. The morphology of the Argentinean Payen flows were compared with lava flows on Daedalia Planum (Mars), using Thermal Emission Imaging System (THEMIS), Mars Orbiter Laser Altimeter (MOLA), Mars Orbiter Camera (MOC), Mars Reconnaissance Orbiter (MRO)/High-Resolution Imaging Science Experiment (HiRISE). THEMIS images were used to map the main geological units of Daedalia Planum and determine their stratigraphic relationships. MOLA data were used to investigate the topographic surface over which the flows propagated and assess the thickness of lava flows. Finally, MOC and MRO/HIRISE images were used to identify inflations fingerprints and assess the cratering age of the Daedalia Planum’ s youngest flow unit which were found to predate the caldera formation on top of the Arsia Mons. The identification of similar inflation features between the Daedalia Planum and the Payen lava fields suggests that moderate and long lasting effusion rates coupled with very efficient spreading processes could have cyclically occurred in the Arsia Mons volcano during its eruptive history. Consequently the effusion rates and rheological proprieties of Daedalia lava flows, which do not take into account the inflation process, can be overestimated. These findings raise some doubts about the effusion rates and lava rheological properties calculated on Martian flows and recommends that these should be used with caution if applied on flows not checked with high-resolution images and potentially affected by inflation. Further HiRISE data acquisition will permit additional analysis of the flow surfaces and will allow more accurate estimates of effusion rates and rheological properties of the lava flows on Mars particularly if this data is acquired under a favourable illumination. [Copyright &y& Elsevier]

Slope streaks are albedo features that form frequently on equatorial Martian slopes. Most slope streaks are dark relative to surrounding terrains, a minor fraction is bright, and there are rare transitioning streaks that exhibit a contrast reversal partway downslope. Their formation mechanisms and physical surface properties are not well understood. New observations acquired by the Colour and Stereo Surface Imaging System (CaSSIS) on board ESA's ExoMars Trace Gas Orbiter (TGO) provide insights into slope streaks' surface microstructure, roughness and particle size ranges. Using multiple phase angle observations, we show that dark slope streaks are substantially rougher and possibly more porous than their bright counterparts, which are likely composed of more compact regolith. Color data acquired in the four wavelength bands suggest that dark streaks are spectrally similar to bright streaks but are composed of larger particles. The comparison of our orbital results to the laboratory measurements of Martian regolith analogs indicates that particles within dark slope streaks may be up to a factor of four larger than the granular material of the surrounding terrains. At one study site in Arabia Terra, using complementary imagery from other orbiters, we identify a case where dark slope streaks turned fully bright in a twenty-year period. These and CaSSIS observations suggest that bright slope streaks are old dark slope streaks, likely formed by deposition of dust or decomposition of surface aggregates into smaller particles. [Display omitted] • We report first CaSSIS observations of Martian slope streaks. • We identified a site where dark streaks turned fully bright in a twenty-year period. • Dark streaks are possibly composed of more porous and rough Martian soil. • Laboratory measurements of Martian simulant indicate particle size effects. • Bright streaks are more compact but of similar grain sizes relative to the surrounding terrains. [ABSTRACT FROM AUTHOR]

Abstract: Mariner 10, the only spacecraft that ever passed close to Mercury, revealed several unexpected characteristics: an intrinsic magnetosphere, the highest mean density of any Solar System terrestrial planet and a very thin non-collisional atmosphere. Mercury''s atmosphere is very poorly explored since only three atomic elements, H, He and O, were observed during the three flybys of Mariner 10. The measurements done by radio and solar occultations provided upper limits on the neutral and ion densities. These measurements pointed out the close connection between species in Mercury''s exosphere and its surface, which is also the case for the Moon. Mariner 10 observations also characterized the vertical distributions and the day to night contrasts of Mercury''s exosphere for its lightest components H and He (Broadfoot, A.L., et al., 1976. Mariner 10: Mercury atmosphere. Geophys. Res. Lett. 3, 577–580). More than a decade later, the first observation from a ground-based observatory of Mercury''s sodium (Na) exospheric component was reported (Potter, A.E., Morgan, T.H., 1985. Discovery of sodium in the atmosphere of Mercury. Science 229, 651–653). Since then, potassium and more recently calcium have been identified in Mercury''s exosphere. The bright Na resonant scattering emission has been often observed since 1985. This large set of observations is now the best source of information on Mercury''s exospheric mechanisms of ejection, dynamics, sources and sinks. In particular, several of these observations provided evidence of prompt and delayed effects, both localized and global, for the very inhomogeneous Mercury''s Na exosphere. These inhomogenities have been interpreted as the trace of Mercury''s magnetosphere–solar wind interaction and have highlighted some of the main sources of exospheric material. Some of these features have been also interpreted as the trace of a global dayside to night side circulation of Mercury''s exosphere and therefore have highlighted also the relation between exospheric production and upper surface composition. Hopefully, new sets of in situ measurements will be obtained within the next decade thanks to Messenger and Bepi-Colombo missions. Until then, ground-based observations and modelling will remain the only approaches to resolve questions on Mercury''s exosphere. Mercury''s exospheric composition and structure as they are presently known are described in this paper. The principal models for the main short and long times terms variations and local and global variations of Mercury''s exosphere are described. The mechanisms of production and their characteristics are also given. Mercury''s exosphere can also be seen as part of the coupled magnetosphere–upper surface–exosphere system and several of the links between these elements are essential to the interpretation of most of the ground-based observations. The relation between Mercury''s planet composition and its exospheric composition is also considered, as is the global recycling, sources and sinks of Mercury''s exosphere. [Copyright &y& Elsevier]

Landslides are common features found on steep slopes on Mars and the role of water in their formation is an open question. Our study focuses on three young martian landslides whose mechanism of formation is unknown and knowing their formation mechanism could give us key information on recent martian climate and/or tectonics. They are less than 5 ​km long, and formed during the Late Amazonian Epoch, with an age <20 ​Ma when Mars is thought to have had a hyperarid climate. To better understand the dynamics and formation mechanism of these landslides, we combine two approaches: geomorphic comparison between martian and terrestrial landslides using remote sensing data from the High Resolution Imaging Science Experiment (HiRISE) and the Colour and Stereo Surface Imaging System (CaSSIS), and numerical modelling using a dry granular flow dynamical model. Our geomorphic analysis revealed two contrasting morphologies suggesting differing dynamics and formation mechanisms. Two of the three martian landslides resemble terrestrial rockslides, while the third is more akin to terrestrial mudslides. The numerical modelling, although not fully conclusive, broadly supports our interpretations from the morphological observations. We suggest that the two landslides resembling terrestrial rockslides could have been triggered by shaking by meteorite impact or marsquakes in the absence of water. On the contrary, we suggest liquid water (originating from ground-ice melted by geothermal heat flux) may have been involved in the initiation of the landslide resembling a terrestrial mudslide. Our results show the value of using morphological comparison between martian and terrestrial landslides combined with numerical modelling to inform the hypotheses of landslide-formation on Mars where in situ analysis is not usually possible. • Three Amazonian martian landslides have similarities with terrestrial analogues. • Landslides' morphology suggests two dynamics and formation mechanisms. • Liquid water may be implied on recent martian landslide formation as for mudflows on Earth. • Young landslide could give key information on recent martian climate and/or tectonics. [ABSTRACT FROM AUTHOR]

The topographic correction of satellite images has to be applied to both disentangle albedo features from illumination effects induced by local topography and perform spectrophotometric analyses of planetary surfaces. This work focuses on the modeling and removal of surface brightness variations induced by topography, referred as topographic shading, from high resolution images of Mars. Topographic shading can be modeled through functions of the surface illumination and observation angles called disk functions. We consider four disk functions that are widely used in planetary photometry: the Lambert, Lommel-Seeliger, Akimov and Minnaert disk functions. We test and evaluate their performances in removing topographic shading from High Resolution Imaging Science Experiment (HiRISE) and Colour and Surface Science Imaging System (CaSSIS) images. We here validate our method, moreover, we report scientific applications to single or multi-band datasets by analyzing topographically corrected HiRISE colour observations of Martian recurring slope lineae and dust devil tracks, as well as CaSSIS panchromatic observations. • We present a methodology to apply the topographic correction to planetary images. • We apply our method to correct HiRISE and CaSSIS images from topographic shading. • We validate our method with published photometry of Martian Recurring Slope Lineae. • The corrected images allow to study the photometry of Martian albedo features. • Multi-band photometry of Recurring Slope Lineae hints towards a dry-dust origin. [ABSTRACT FROM AUTHOR]

"LICIACube – the Light Italian Cubesat for Imaging of Asteroids" is managed by the Italian Space Agency (ASI) and will be part of the NASA DART mission, with the aim of i) documenting the DART impact's effects on the secondary member of the (65803) Didymos binary asteroid system, ii) characterizing the shape of the target, and iii) performing dedicated scientific investigations on it. DART probe will be launched at the end of 2021 and LICIACube will be hosted as piggyback during the interplanetary cruise, then released 10 days before the impact, and autonomously guided along its fly-by trajectory. The LICIACube payload is composed by LEIA, a narrow FoV camera, and LUKE, a wide FoV imager with an RGB Bayer pattern filter, that will collect and transmit to Earth several unique images of the effects of the DART impact on the asteroid, such as the formation and the development of the plume potentially determined by the impact. LICIACube will be the first deep space mission developed and autonomously managed by an Italian team: the design, integration and test of the CubeSat have been assigned by ASI to the aerospace company Argotec, while the LICIACube Ground Segment has a complex architecture based on the Argotec Mission Control Center, antennas of the NASA Deep Space Network and data archiving and processing, managed at the ASI Space Science Data Center. The LICIACube team includes a wide Italian scientific community, involved in the definition of all the aspects of the mission: trajectory design; mission definition (and real-time orbit determination during operations); impact, plume and imaging simulation and modelling, in preparation of a suitable framework for the analysis and interpretation of in-situ data. The major technological mission challenge, i.e. the autonomous targeting and imaging of such a small body during a fast fly-by, to be accomplished with the limited resources of a CubeSat, is affordable thanks to a strong synergy of all the mentioned teams in support of the engineering tasks. - LICIACube is the first purely Italian spacecraft operating in deep space. -LICIACube is managed by the Italian Space Agency and will be part of the NASA DART mission. -It will analyze the output of the first kinetic impact test at a realistic scale. -The payload is composed by LEIA, a narrow FoV camera, and LUKE, a wide FoV imager with an RGB Bayer pattern filter. -Aims: documenting the DART impact on Dimorphos; characterizing the target shape; performing scientific investigations. [ABSTRACT FROM AUTHOR]

An innovative photogrammetric pipeline has been developed by INAF-Padova for the processing of the stereo images from the CaSSIS (Colour and Stereo Imaging System) (Thomas et al., 2014). CaSSIS is the multispectral stereo push frame camera on board ExoMars TGO (Trace Gas Orbiter) which will image 1.5% of the Mars surface in stereo mode with a spatial resolution of 4.6 ​m/pixel: the highest resolution single pass stereo capability currently operating at Mars. Data acquisition started in April 2018. The camera is able to provide two images of the same target from two different points of view along the same orbit and within one minute. The telescope is mounted on a rotational stage and its boresight is oriented to 10° with respect to nadir direction. After the acquisition of the first set of images looking forward along track, the rotational stage is rotated by 180° and a second set of images (looking backward) is acquired. The stereo pairs can then be processed to provide the 3D topography of specific targets. The suite of photogrammetry and imaging tools, named 3DPD (3Dimensional reconstruction of Planetary Data) (Simioni et al. 2017), is designed for processing stereo push frame data and producing the three-dimensional data for geomorphological analysis of planetary surfaces. The workflow involves a MATLAB tool for the preparation of the inputs (the mosaicked images and the projection matrices) to be ingested into the 3DPD matching core software. The pipeline is in continuous development and routinely ingests a large number of images that CaSSIS is presently acquiring and will continue to acquire in the future. CaSSIS 3DPD products are the unique DTMs available nowadays and the stereo products have been considered in some scientific work (as described in Section 6.2). The same pipeline faces the need of a dedicated pipeline for the Mercury Global Mapping with the Spectrometers and Imagers for the Mercury Planetary Orbiter (MPO) BepiColombo Integrated Observatory SYStem (SIMBIO-SYS) (Cremonese et al., 2020). [Display omitted] • 3-dimensional reconstruction software for planetary surfaces. • High resolution DTMs of targets on the Mars surface provided by CaSSIS Stereo Camera images. • Photogrammetric pipeline for push frame instruments from CaSSIS to Bepicolombo stereo camera STC/SIMBIOSYS. • Archiving of the Digital Terrain Models obtained by the CaSSIS stereo pairs. [ABSTRACT FROM AUTHOR]

Grooves represent the evidence of tectonic activity that deformed Ganymede surface during its geologic evolution. In this work, we investigate the main characteristics of Ganymede's groove populations on four different areas located at the equatorial region of the satellite (Uruk Sulcus, Babylon Sulci, Phrygia Sulcus and Mysia Sulci). Specifically, we analyse i) the grooves length distribution to provide a framework for their evolution and ii) the grooves self-similar clustering to infer their vertical penetration inside Ganymede icy shell. For each dataset, we find that the grooves distribution is well fitted by an exponential-law and a power-law distribution depending on the structure length. This implies the presence of confined structures in a shallow layer of the icy crust (relatively shorter, exponentially-fitted structures) and crustal-scale structures that could theoretically reach the crust-ocean interface (relatively longer, power law-fitted structures). In addition, the existence of two exponential distributions for few datasets suggest that there could be two different system of structure confined within specific mechanical crust layers. The thickness of the penetrated icy shell is retrieved through the self-similar clustering analysis and ranges between 105 and 130 ​km for the examined datasets. This value agrees with independent estimates of the icy shell thickness, ranging between 80 and 150 ​km. Moreover, our results support the hypothesis that a large number of grooves penetrate the brittle icy crust, with sets of fractures vertically confined in different mechanical layers, while the penetration of few interconnected faults underlying longer grooves may interest the whole icy crust above the liquid ocean. • Ganymede's grooves are the representation of a hierarchical system. • Shorter grooves are vertically confined in the brittle icy crust. • Longer grooves are crustal-scale structures theoretically reaching the crust-ocean interface. • The icy shell thickness interested by grooves penetration is between 105 and 130 ​km. [ABSTRACT FROM AUTHOR]

We present a multidisciplinary analysis of Lermontov crater, located at 15.24°N, −48.94°E in the Kuiper quadrangle of Mercury. By means of MESSENGER multiband MDIS-WAC and monochrome MDIS-NAC images, we prepare a high-resolution geological map of the crater and its closest surroundings, highlighting the presence of coexisting hollows and pyroclastic deposits on its floor. On the photometrically corrected MDIS-WAC multiband dataset, we apply an unsupervised clustering technique that spectrally separates the different materials located both inside and outside Lermontov crater. We observe that the pyroclastic deposits located on the crater's floor have a steep, red spectral behaviour dominated by the presence of a mixture of various pyroxenes containing Ti and Ni. On the contrary, the vents' rims are characterised by several hollows whose spectral slope is bluer than that of the pyroclastic deposits. By comparing the vent hollows to the hollows located farther out on the crater floor, we observe a steeper 0.62–0.82 ​μm spectral trend for those within the vents. The vent hollows' spectrum is more similar to the pyroclastic one in the above mentioned wavelength range. In addition, the vent hollows 0.55 ​μm absorption band could be related to CaS, while the small differences in slope at 0.48 ​μm and 0.62 ​μm could be due to the presence of other volatiles compounds, such as MgS or chlorides. When compared to hollows located in other hermean geological settings, Lermontov hollows are characterised by steeper spectra. This supports the interpretation that when hollows form, their bright deposits do not completely overwrite the spectral signature of the surrounding terrain, and their spectroscopic appearance is mixed with the composition of the terrain where they form. • First high-resolution geological map of Lermontov crater and its surroundings. • Clustering technique to investigate the Lermontov pyroclastic deposits and the coexisting hollows through MESSENGER/MDIS. • Different mineralogical composition of pyroclastic deposits, field and vent hollows. [ABSTRACT FROM AUTHOR]