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

NASA’s Dawn spacecraft acquired images and hyperspectral data of Ceres by means of FC and VIR instruments, and identified some widespread bright areas or bright spots (BS). The most peculiar BS is inside Occator crater and it is characterized by spectral properties very dissimilar from the rest of Ceres’ surface. To perform a mineralogical analysis, absorption bands in reflectance spectra must be properly isolated by removal of continuum, and related descriptors (such as band centers and band depths) can be computed. The method for continuum removal must be applicable to all Ceres spectra, relative to different areas, so that a comparison among spectral parameters can be made and mineralogical interpretation can be achieved. This work focuses on the definition of the most appropriate continuum to isolate absorption bands located at ∼3.1, ∼3.4 and ∼4.0 µm. The ∼3.1 µm feature is related to ammoniated phyllosilicates, while the ∼3.4 and ∼4.0 µm absorption bands are indicative of carbonates. Thermal emission affects the continuum for these bands in the VIR spectral range, which extends up to 5.1 µm, moreover all thermal-removed reliable data stop at 4.2 µm. This implies that the shoulder of bands at longer wavelength cannot be identified. We therefore defined alternative continua, i.e., a linear and two polynomial ones, able to describe spectra of any area (i.e. bright or dark) and regardless of spatial resolution. We found that the linear definition satisfies these requirements best. For the first time, we performed an error evaluation on band depths and band centers introduced by the applied method, which is relevant for comparison of spectral parameters of Ceres regions and to better interpret mineralogy and photometric effects.

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Olivine is one of the main abundant mineral in the Solar System, and the determination of its abundance on a surface may give fundamental information about its evolution. The study of surface distribution of olivine on asteroid (25143) Itokawa through near-Infrared reflectance spectroscopy is a difficult goal because olivine and pyroxene bands centred at 1 μm and 2 μm are not entirely included in Hayabusa/NIRS’ spectral range. In this work, the retrieval of olivine abundance has been performed by applying two different methods: the first one uses some spectral indices to retrieve olivine abundance, whilst the second one consists of the application of the Hapke’s theory in order to create synthetic spectra aimed at fitting a selection of NIRS’ spectra. The analysis performed with the first method brought to an approximately homogeneous distribution of olivine content (60 ± 15% on average) on Itokawa’s surface, with the exception of Sagamihara region, which has a slightly (up to 10%) lower olivine content. The second method brought to an average 60 ± 7.5% olivine content within 5 selected spectra, with the same reduction found in the spectrum from the Sagamihara region. All these values are in agreement with literature values on this topic, especially with the ones retrieved from particles sampled in Muses Sea by the Hayabusa probe.

We characterized 67P/Churyumov-Gerasimenko's cometary activity during its inbound arc before perihelion (2014 August-2015 January). We focused on the geomorphological regions of the Northern hemisphere observed by the ESA/Rosetta space probe during this time period. The GIADA dust detector characterized the physical properties of the fluffy and compact particles ejected from the nucleus; the VIRTIS imaging spectrometer detected exposed water ice.

The Near-Earth Asteroid 162173 Ryugu (1999 JU3) was investigated by the JAXA Hayabusa2 mission from June 2018 to November 2019. The data acquired by NIRS3 spectrometer revealed a dark surface with a positive near-infrared spectral slope. In this work we investigated the spectral slope variations across the Ryugu surface, providing information about physical/chemical properties of the surface. We analysed the calibrated, thermally and photometrically corrected NIRS3 data, and we evaluated the spectral slope between 1.9 μm and 2.5 μm, whose values extend from 0.11 to 0.28 and the mean value corresponds to 0.163±0.022. Starting from the mean value of slope and moving in step of 1 standard deviation (0.022), we defined 9 “slope families”, the Low-Red-Slope families (LR1, LR2 and LR3) and the High-Red-Sloped families (HR1, HR2, HR3, HR4, HR5, HR6). The mean values of some spectral parameters were estimated for each family, such as the reflectance factor at 1.9 μm, the spectral slope, the depth of bands at 2.7 μm and at 2.8 μm. A progressive spectral reddening, darkening and weakening/narrowing of OH bands is observed moving from the LR families to the HR families. We concluded that the spectral variability observed among families is the result of the thermal metamorphism experienced by Ryugu after the catastrophic disruption of its parent body and space weathering processes that occurred on airless bodies as Ryugu, such as impact cratering and solar wind irradiation. As a consequence, the HR1, LR1, LR2 and LR3 families, corresponding to equatorial ridge and crater rims, are the less altered regions on Ryugu surface, which experienced the minor alteration and OH devolatilization; the HR2, HR3, HR4, HR5 families, coincident with floors and walls of impact craters, are the most altered areas, result of the three processes occurring on Ryugu. The strong reddening of the HR6 family (coincident with Ejima Saxum) is likely due to the fine-sized material covering the large boulder.

This paper presents the VISTA (Volatile In Situ Thermogravimetry Analyser) instrument, conceived to perform planetary in-situ measurements. VISTA can detect and quantify the presence of volatile compounds of astrobiological interest, such as water and organics, in planetary samples. These measurements can be particularly relevant when performed on primitive asteroids or comets, or on targets of potential astrobiological interest such as Mars or Jupiter's satellite Europa. VISTA is based on a micro-thermogravimetry technique, widely used in different environments to study absorption and sublimation processes. The instrument core is a piezoelectric crystal microbalance, whose frequency variations are affected by variations of the mass of the deposited sample, due to chemical processes such as sublimation, condensation or absorption/desorption. The low mass (i.e. 40 g), the low volume (less than 10 cm3) and the low power (less than 1 W) required makes this kind of instrument very suitable for space missions. This paper discusses the planetary applications of VISTA, and shows the calibration operations performed on the breadboard, as well as the performance tests which demonstrate the capability of the breadboard to characterize volatile compounds of planetary interests. © 2015, Springer Science+Business Media Dordrecht.

Piezoelectric Crystal Microbalances (PCM’s) are widely used to study the chemical processes involving volatile compounds in any environment, such as condensation process. Since PCM’s are miniaturized sensor, they are very suitable for planetary in situ missions, where can be used to detect and to measure the mass amount of astrobiologically significant compounds, such as water and organics. This work focuses on the realization and testing of a new experimental setup, able to characterize volatiles which can be found in a planetary environment. In particular the enthalpy of sublimation of some dicarboxylic acids has been measured. The importance of dicarboxylic acids in planetology and astrobiology is due to the fact that they have been detected in carbonaceous chondritic material (e.g. Murchinson), among the most pristine material present in our Solar System. In this work, a sample of acid was heated in an effusion cell up to its sublimation. For a set of temperatures (from 30 °C to 75 °C), the deposition rate on the PCM surface has been measured. From these measurements, it has been possible to infer the enthalpy of sublimation of Adipic acid, i.e. ΔH = 141.6 ± 0.8 kJ/mol and Succinic acid, i.e. ΔH = 113.3 ± 1.3 kJ/mol. This technique has so demonstrated to be a good choice to recognise a single compound or a mixture (with an analysis upstream) even if some improvements concerning the thermal stabilization of the system will be implemented in order to enhance the results’ accuracy. The experiment has been performed in support of the VISTA (Volatile In Situ Thermogravimetry Analyzer) project, which is included in the scientific payload of the ESA MarcoPolo-R mission study.

International audience; The dwarf planet Ceres is an airless body composed of Mg-phyllosilicates, NH4-phyllosilicates, Mg/Ca-carbonates and a dark component. The subsurface of Ceres, investigated by the material composing the peak of complex craters (ccp, crater central peak material; Galiano et al., 2019), reveals a composition similar to the surface, with an increasing abundance of phyllosilicates in the interior. A moderate trend between age of craters’ formation and spectral slope of ccps suggests that younger ccps show a negative/blue slope and older ccps are characterized by positive/red slope. To investigate the causes of different spectral slope in ccps, different grain-sized Ceres analogue mixtures were produced and spectrally analysed. First, the end-members of the Ceres surface (using the antigorite as Mg-phyllosilicate, the NH4-montmorillonite as NH4-phyllosilicate, the dolomite as carbonate and the graphite as dark component), were mixed, obtaining mixtures with different relative abundance, and identifying the mixture with the reflectance spectrum most similar to the average Ceres spectrum. The selected mixture was reproduced with grain size of 0–25 μm, 25–50 μm and 50–100 μm. The three mixtures were heated and spectrally analysed, both with an acquisition temperature of 300 K (room temperature) and 200 K (typical for surface Ceres temperature during VIR observations). The best analogue Ceres spectrum is coincident with a mixture composed of 18 M% (mass percentage) of Dolomite, 18 M% of Graphite, 36 M% of Antigorite and 28 M% of NH4-montmorillonite, after experiencing a heating process. The heating process produces: 1) a darkening and reddening of spectrum, as consequence of the devolatilization of OH group in phyllosilicates and a more dominant effect of opaque phase; 2) a deepening in the intensity of the 3.4 and 4.0 μm band, as well as the 2.7 and the 3.1 μm band, likely due to the loss of absorbed atmospheric water; 3) narrowing of 3.1 μm band and the shift of band center toward longer wavelength (i.e. at 3.06 μm) coincident with mean Ceres spectrum, related to the loss of absorbed atmospheric water. The analysis of the best Ceres analogue mixture, reproduced at different grain size and after heating process, reveals a weakening of 2.7, 3.1, 3.4 and 4.0 absorption bands in coarser samples, likely related to large size of dark grains which reduce the spectral contrast. Furthermore, spectra of coarser mixtures are more red-sloped, suggesting that this trend is more affected by the dark component. The best analogue Ceres mixture produced in this work is almost coincident with the mean spectrum of Haulani ccp, the youngest ccps on Ceres and therefore representative of less altered material on Ceres. The redder spectral slope observed in the older ccps is probably the consequence of the space weathering effects on the original material composing the peak.