Context. Near-Earth objects (NEOs) are the most accessible small Solar System bodies by both spacecrafts and ground-based telescopes. Close encounters of these objects with Earth represent opportunities to characterize their physical and mineralogical properties. They are also a constant threat to humanity due to possible impact events with Earth. In this context, the NEOROCKS project has been financed by the European Union's Horizon 2020 research and innovation program. Aims. We present the final results on photometry of the NEOROCKS project, with the aim of extending the dataset of surface colors for small NEOs with unknown properties and, when possible, characterizing newly discovered NEOs. Methods. Photometric observations were performed using the 1.2 m telescope at the Haute-Provence observatory (in France) in the BVRI filters of the Johnson-Cousins photometric systems between May 2022 and June 2023. The stability and dynamics of objects from the NEOROCKS database was investigated by numerical integration. Results. We obtained new surface colors for 83 NEOs. Overall, the NEOROCKS color database contains 170 objects. The majority of the objects in the dataset with diameters D<500 m belong to a group of silicate bodies. We estimated the unbalanced percentage between S- and C-type objects as an observational bias due to reflective proprieties of the surface of objects. The average of Lyapunov time of about 100 years is evidence of highly chaotic orbits of objects from the color database of NEOROCKS. Asteroid 2011 OL51 has a reasonable probability of being a parent body contributor to the October Capricornidis meteor shower. Asteroids 2004 HK33, 2022 VV (D-type), 2003 WR21, and 2017 SE1 (A-type) belong to end-member classes and have Delta V<7 km/s; thus, they are possible candidates for in situ investigations.

.IntroductionNASA’s OSIRIS-REx (Origins, Spectral Interpretations, Resource Identification, and Security–Regolith Explorer) asteroid sample return mission (Lauretta et al., 2017) began operating in proximity to near-Earth asteroid (101955) Bennu in December 2018. Here we present an analysis of the global photometry of Bennu from measurements by the OSIRIS-REx Visible and InfraRed Spectrometer (OVIRS; Reuter et al., 2018). This instrument is a point spectrometer with a wedged filter design. OVIRS is used for the spectral characterization of the surface of Bennu, with a field of view of 4 mrad and an effective spectral range from 0.4 to 4.3 μm. Our work focuses on OVIRS data acquired from December 9, 2018, to September 26, 2019.2.DatasetThis study comprises the global observation data from Preliminary Survey and the two sub-phases of Detailed Survey, Baseball Diamond (BBD) and Equatorial Stations (EQ) (campaigns described in Lauretta et al., 2017). We use a total of 299,702 calibrated spots. More details about the data selection and calibration are introduced by Zou et al. (submitted).3.Photometric analysesWe model the scattering properties of the surface of Bennu using the Lommel-Seeliger, Minnaert, McEwen, and Akimov photometric models. The best-fit model is a McEwen model with an exponential phase function and an exponential polynomial partition function. We use this model to correct the OVIRS spectra of Bennu to a standard reference viewing and illumination geometry at visible to infrared wavelengths for the purposes of global spectral mapping (Figure 1). We derive a bolometric Bond albedo map in which Bennu’s surface values range from 0.021 to 0.027. We find a phase reddening effect of 1.4±0.3 × 10−4 μm−1deg−1 across the wavelength range 0.48 to 2.5 μm, and our model is effective at removing this phase reddening.We compare our OVIRS results to Golish et al. (2020)’s report on the global photometry of Bennu, based on imaging data from the OSIRIS-REx Camera Suite (OCAMS; Rizk et al., 2018). We also compare the results to ground observation and other minor planets including Ryugu.Acknowledgements: This material is based upon work supported by NASA under Contract NNM10AA11C issued through the New Frontiers Program. We are grateful to the entire OSIRIS-REx Team for making the encounter with Bennu possible and the exploration highly successful. X.-D. Zou and J.-Y. Li also acknowledge partial support from the Solar System Exploration Research Virtual Institute 2016 (SSERVI16) Cooperative Agreement (Grant NNH16ZDA001N), SSERVI-TREX to the Planetary Science Institute. M. A. Barucci acknowledges funding support from CNES. ReferencesBennett, C.A., et al. 2020. A high-resolution global basemap of (101955) Bennu. Icarus. doi: 10.1016/j.icarus.2020.113690.Ernst et al., 2018, The Small Body Mapping Tool (SBMT) for Accessing, Visualizing, and Analyzing Spacecraft Data in Three Dimensions, LPSC 49, abstract no. 1043.Golish, D.R., et al. 2020. Disk-resolved photometric modeling and properties of asteroid (101955) Bennu. Icarus, doi:10.1016/j.icarus.2020.113724.Lauretta, D.S., et al. 2017. OSIRIS-REx: sample return from asteroid (101955) Bennu. Space Science Reviews 212(1-2):925-984.Reuter, D.C., et al. 2018. The OSIRIS-REx Visible and InfraRed Spectrometer (OVIRS): spectral maps of the asteroid Bennu. Space Science Reviews 214(2):54.Rizk, B., et al. 2018. OCAMS: the OSIRIS-REx Camera Suite. Space Science Reviews 214(1):26.Zou et al. (submitted). Photometry of asteroid (101955) Bennu with OVIRS on OSIRIS-REx. Icarus.Figure 1. A global 3D facet-based map of the photometrically corrected (to 30°, 0°, 30°) OVIRS spots at a wavelength of 0.55 μm. The data are overlain on the OCAMS imaging basemap (Bennett et al., 2020), as viewed in the Small Body Mapping Tool (Ernst et al. 2018). Input spectra were obtained during Detailed Survey EQ3.

The MIRS (MMX InfraRed Spectrometer) infrared spectrometer is part of the scientific payload of JAXA's (Japanese Space Agency) Martian Moon eXploration (MMX) mission. From the reflected sunlight by the planetary surfaces, MIRS will provide information on the Mars atmosphere and the mineralogy and chemistry of its moons. Spectra carried out by the instrument (0.9-3.6 mu m) include the thermal emission from the surface, which needs to be modelled and removed to extract the compositional information. In this study, to find an efficient and rapid way to thermally correct infrared data, we developed a simple thermal emission correction based on blackbody fits, and quantify its relative error. To test the method, we generated synthetic spectra of Phobos by using a thermophysical model. We found that the method can produce reflectance spectra with only a few per cent errors, although some undercorrection of the thermal contribution is observed. Compositional information may still be retrieved through the position of absorption bands, despite the thermal emission correction can leave some uncertainties in its strength. We conclude that the method could be used for a first and quick analysis for interpretation of the MIRS data. We also applied our thermal correction methodology to real CRISM (Compact Reconnaissance Imaging Spectrometer for Mars) observations of Phobos. The method looks reliable with a satisfactory removal of the thermal contribution, confirms the presence of an absorption band centred around 2.8 mu m, and reveals an apparent absorption at 3.2 mu m. However, we are not able to confirm the reality of the 3.2 mu m band at this stage, because of the presence of an artefact in CRISM data.

Aims. This study aims to determine the size, albedo, and rotational period of (98943) 2001 CC21, a target of the Hayabusa2 extended mission, using thermal data from the Spitzer Space telescope and ground-based observations. Methods. The Spitzer data were acquired with the Infrared Spectrograph in the 6-38 mu m range, reduced using the Spitzer pipeline, and modeled with the near-Earth asteroid thermal model to determine the asteroid size and albedo. The absolute magnitude and rotational period were determined thanks to new observations carried out at the 3.5 m New Technology Telescope, the 1.2 m Observatoire de Haute Provence, and the 0.7 m Abastumani telescope. Three complete light curves were obtained in 2023 and 2024 at the last-mentioned telescope. Results. We determine an absolute magnitude of H = 18.94 +/- 0.05 and a rotational period of 5.02124 +/- 0.00001 hours, with a large light curve amplitude of similar to 0.8 mag. at a phase angle of 22 degrees, indicating a very elongated shape with an estimated a/b semiaxis ratio >= 1.7, or a close-contact binary body. The emissivity of 2001 CC21 is consistent with that of silicates, and its albedo is 21.6 +/- 1.6%. Finally, the spherical-equivalent diameter of 2001 CC21 is 465 +/- 15 m. Conclusions. The albedo value and emissivity determined here, coupled with results from polarimetry and spectroscopy from the literature, confirm that 2001 CC21 is an S-complex asteroid, and not an L-type one as was previously suggested. The size of 2001 CC21 is less than 500 m, which is smaller than its first size estimation (similar to 700 m). These results are relevant in preparation of the observing strategy for 2001 CC21 of the Hayabusa2 extended mission.

The Martian Moon eXploration mission (MMX), currently developed by the Japan Aerospace Exploration (JAXA) will aim at studying Mars satellites and return samples from Phobos to decipher the history of the Martian system. MMX mission is to be launched in September 2024 and arrive in Mars system on August 2025, will stay three years in Quasi Satellite Orbits (QSO) around Phobos, and will land for several hours on Phobos to collect at least 10g of Phobos regolith before returning to Earth.Among the mission instrument suite is the near-Infrared Spectrometer MIRS (MMX InfraRed Spectrometer) provided by CNES and built at LESIA-Paris Observatory in collaboration with four other French laboratories (LAB, LATMOS, LAM, IRAP-OMP) and in close collaboration with JAXA and MELCO. MIRS is an imaging spectrometer from 0.9 to 3.6 µm, with a spectral resolution better than 20 nm. The IFOV is 0.35 mrad and FOV of +/-1.65°. The SNR is higher than 100 up to 3.2 µm in a maximum integration time less than 2s. For Mars observation MIRS is expected to perform observations at 10 km spatial resolution, with a spectral radiometric absolute and relative accuracies of 10% and 1% respectively.Given MIRS spectral range, expected Signal-to-Noise ratio, and observation windows, a certain numbers of high priority targets have been set to achieve MMX goal of Constrain transport processes for dust and water near the Martian Surface, continuous observations of the mid-to low-latitude distributions of dust storms, ice clouds and water vapor in the Martian atmosphere (Barucci et al. 2021, Ogohara et al. 2021), summarized in Table 1. Simulated spectra of Martian atmosphere as observed by MIRS are provided in Figure 1. Table 1: List of MIRS main science targets for Mars observations (adapted from Barucci et al. 2021). Target Parameters Spectral range Ice cloud formation and evolution Water ice 1.5, 2 and 3 µm Dust clouds / storms formation and evolution Dust CO2 band @2.7 µm 0.9-3.6 µm continuum Water cycle H2O vapor 2.6 µm Atmospheric dynamics and composition Surface pressure CO2 band @ 2.0 µm CO 2.3 µm Limb observations for middle atmosphere O2 day-glow 1.27 µm Figure 1: Simulated MIRS spectra for typical Mars observation (from Barucci et al. 2021). Plain curves correspond to clear sky conditions, and the dashed ones include the effects of dust or water ice clouds. For gases, CO2, CO, and water vapor are calculated separately and reported in red, orange, and blue curves, respectively.MMX QSO around Phobos will result in a quasi-circular orbit around Mars with a period of ~7h, providing more than 3 hours window to Mars observation when Phobos observation is not possible. Several observation strategies, still in discussion, will be possible to maximize either temporal or spatial coverage of Mars and its atmosphere by MIRS. These strategies span from observations with a 30 minutes temporal resolution of a limited zone, to a complete coverage for low and mid latitude in a few orbits (Ogohara et al. 2021, Barucci et al. 2021). Limb observations may also be performed to obtain high vertical resolution observations of the Martian atmosphere.MIRS observations will provide further constraints on dust and water transport processes in the Martian atmosphere, by monitoring the distributions of dust content and storms, water ice clouds and water vapor. CO2 (and thus pressure) will be monitored through the CO2 2.0 µm band. Water vapor will be monitored on a daily basis using its 2.6 µm band (Maltagliati et al. 2008) and water ice clouds through their spectral features between 0.9 and 3.6 µm (Olsen et al. 2019). MIRS should also be able to detect CO 2.35 µm and O2 at 1.27 µm. MIRS spectra will also allow for estimations of the water adsorbed in the surface regolith. Finally, MIRS will be operated in close collaboration with the OROCHI (Optical Radiometer composed of Chromatic Imagers) and TENGOO (Telescopic Narrow Angle Camera) instruments. This will enable efficient monitoring and reactivity to investigate short lifespan events in Martian atmosphere. This will also render possible the investigation of CO2 clouds following the procedure proposed by Vincendon et al. 2011 for Mars Express observations.The reflectance spectrum from the light backscattered by atmospheric aerosols can be obtained by comparing successive observations of identical zones on Mars within a short time and with varying phase angles. Such a set of measurements permits to decorrelate the surface reflectance signal from the light scattered by the aerosols suspended in the atmosphere and gives information on the aerosols size and their composition properties averaged over the line of sight. Previous measurements showed a particle size distribution having an effective radius of 1.2±0.2 μm (Erard et al. 1994). The retrieved parameters include the scattering albedo, the phase function of the aerosols, the optical thickness, τ, of the atmosphere at the time of observation and the aerosols size distribution.In summary, MIRS observations, together with the ones from MSA, OROCHI and TENGOO, will help better understand the interdependencies of species and their roles in the Martian water, CO2 and dust cycles, thanks to long term monitoring of these key constituents of Mars atmosphere.ReferencesBarucci et al. 2021, MIRS an Imaging Spectrometer for the MMX mission, accepted for publication in Earth Planets and SpaceErard, S., Mustard, J., Murchie, S., Bibring, J. P., Cerroni, P., & Coradini, A. (1994). Martian aerosols: Near-infrared spectral properties and effects on the observation of the surface. Icarus, 111(2), 317-337.Ogohara et al. 2021, The Mars system revealed by the Martian Moons eXploration mission, accepted for publication in Earth Planets and SpaceVincendon et al. 2011, New near-IR observations of mesospheric CO2 and H2O clouds on Mars, JGR Planets 116, 0-02.

Introduction: Dark surfaces, such as those found on planets asteroids and other primitive bodies, are the focus of past, present, and future space missions within the Solar System. Understanding the spectroscopic characteristics of these low albedo surfaces remains a significant challenge, with our current knowledge being incomplete. The presence of opaque materials [1] or surface processes like space weathering [2] or thermal alteration [3] often is linked with these dark surfaces. Interpreting remote sensing data necessitates intensive laboratory work, which serves as a pivotal tool in revealing the physical state and composition of these surfaces.Analyzing complex mixtures of analogous materials remains one of the pivotal laboratory investigations to support remote sensing interpretation, but it also represents one of the most challenging experiments, in particular when multiple components are used in the mixtures. We present in this contribution several results from different works that share the common goal of studying how the mixing of different grain size and dark materials can affect the behavior of infrared spectra in the near- to mid-infrared range (1.25-25 μm).Methods: In this presentation, two primary studies will be outlined: the initial investigation delves into the combination of hydrated and anhydrous mineral components with varying grain sizes [4], while the subsequent study examines the blending of basalts with dark components at different grain sizes [5]. Samples prepared for both studies utilize an innovative protocol for mixing two components with distinct grain sizes. This method involves a sequence of steps, including sieving and mineral washing to isolate each grain size, followed by the mixing of the selected components. This procedure allows us to produce unique samples with a bigger grain size covered by a selected amount of small grains (Figure 1).In the first work, we prepared several mixtures using 1 wt% and 5 wt% of hyperfine grain size (< 10 μm) of hydrated minerals and 95 wt% and 99 wt% of larger grain size (200–500 μm) of anhydrous minerals. We measured the IR reflectance spectrum of these mixtures in the range 8000–400 cm−1 (1.25–25 μm). Analysis of the spectroscopic features was carried out independently in two separated ranges covered by our measurements, in the NIR range we focused on the presence of the hydrated band at 2.7 μm while in the MIR range we carried out an analysis of the most important spectroscopic features present. The second sample set includes four series of basaltic mix (feldspar and pyroxene), at different grain sizes from < 50 μm to 500-1000 μm, mixed with amorphous carbon at increasing weight percentages from 1% to 50%. We analyzed several features on the spectrum of each mineral mixture: (i) near infrared slope; (ii) 2.7 μm OH-stretching band; (iii) Christiansen features; (iv) Reststrahlen band and Transparency feature.Figure 1. Secondary electrons SEM image of enstatite sample before (panel A and B) and after mixing with 5% and 1% of serpentine (panel C and D).Results: The results of the first work [4] show how the addition of a hydrated component, which is minor in percentage and has a much smaller grain size, can lead to very remarkable changes in the NIR region especially in increasing the hydrated band depth at 2.7 μm (Figure 2), while slightly affecting the MIR region. The surface of many rocky bodies is covered with regolith, and these new laboratory data show how even a small amount of hydrated mineral in the composition can influence the final spectrum. Measurements presented in the second work [5] point towards a critical effect of dark material but with a different outcome for each grain size of the brighter component of the mixture (Figure 3). For the first time we investigate the spectral range from NIR to MIR. Some of the most interesting results involved the slope trend of modification with dark material, in particular we observed an inversion between reddening and bluing depending on the percentage of the mixture and the grain size. Moreover, we investigated also the different behavior of several features such as: hydrated band at 2.7 μm, the Reststrahlen band and Transparency feature.Conclusion: Enhancing our comprehension of spectroscopic alterations resulting from minor fluctuations in mineral phases is crucial for accurately interpreting remote sensing data gathered from planetary surfaces by space missions. The dataset compiled from our experiments will serve as vital groundwork for interpreting forthcoming data from the JAXA Martian Moon eXploration mission. Additionally, it will aid in comprehending past data from dark surfaces within the Solar System, such as asteroids (162173) Ryugu and (101955) Bennu. Significant laboratory efforts are still required to effectively complement the analysis of remote sensing data, with numerous additional mixtures and combinations slated for investigation as a follow-up to this research. Further laboratory measurements will serve a dual purpose: expanding the database for interpreting planetary surfaces and furnishing reference spectra to enhance and validate current and future models.Figure 2. Detail of hydrated band around 2.7 μm for hydrated minerals serpentine (top panels) and montmorillonite (bottom panels) with grain size

Context . A number of bodies in the Solar System are characterized by dark surfaces, from carbonaceous asteroids to the enigmatic surface of Phobos and Deimos. Our understanding of the spectroscopic behavior of low-albedo surfaces remains incomplete. To improve the interpretation of remote sensing data, laboratory studies continue to serve as a pivotal tool for unveiling the physical state and composition of such surfaces. Aims . Several processes can be simulated in the laboratory, however, the preparation and analysis of a complex mixing of analog material is one of the most fundamental among them, while also being one of the most complex when multiple components are used. In this work, we aim to study how dark material mixed with basaltic material at different grain sizes can affect the spectroscopic features from the near- to mid- infrared (1.25–25 µm). Methods . Our sample set includes four series of basaltic mix (feldspar and pyroxene) at different grain sizes from <50 µm to 1000 µm, mixed with amorphous carbon at increasing weight percentages ranging from 1% to 50%. We analyzed several features on the spectrum of each mineral mixture. In particular, we investigated the behavior of the: (i) near-infrared slope; (ii) 2.7 µm OH-stretching band; (iii) Christiansen features; and (iv) Reststrahlen band and Transparency feature. Results . The measurements presented in this work, which take into account a large wavelength range for the first time, point toward a critical effect of dark material, but with a different outcomes for each grain size. Some of the most interesting results involve the slope trend of modification with dark material and the variant behavior of the Reststrahlen band and Transparency feature. Conclusions . This dataset will offer a key support in the interpretation of data collected on dark surfaces by past and future space missions. This knowledge will be also important in the context of linking analyses of returned samples with remote sensing data collected on planetary surfaces.

Two asteroid sample return missions studied, in-situ, two primitive asteroid targets to unravel their physical and chemical properties as well as obtain regolith samples for return to Earth. We describe remote observations from OSIRIS-REx and Hayabusa2 to determine the hydration content of these primitive asteroid surfaces and implications for their aqueous alteration histories. The NASA mission—Origins, Spectral Interpretation, Resource Identification, and Security–Regolith Explorer—OSIRIS-REx [1] studied the asteroid (101955) Bennu for two and a half years starting on its arrival at the asteroid on December 2018. The sample collection of surface regolith occurred on October 20th 2020 followed by the spacecraft departure from the asteroid on May 10th 2021 to begin its return cruise to deliver the sample to Earth in September 2023. The JAXA mission Hayabusa2 [2] studied the asteroid (162173) Ryugu for a year and a half (June 2018 to November 2019), and the twice-collected regolith samples with the re-entry capsule landed on Earth on December 5th 2020. These samples are currently being analyzed in Earth laboratories. Both missions had a near-infrared spectrometer onboard, amongst other instruments, which are the OVIRS spectrometer (OSIRIS-REx Visible and InfraRed Spectrometer) [3] and the NIRS3 spectrometer (Near-Infrared Spectrometer) [4]. The analysis of the asteroid surface reflectance spectra revealed the presence of an absorption band associated with OH/H2O centered near 2.74 microns [5] for asteroid Bennu and 2.72 microns for asteroid Ryugu [6]. This absorption band is caused by hydrated phyllosilicates across both asteroid surfaces. The absorption band, however, differs in center, shape and strength between the two asteroids with a weak and narrow band in the case of Ryugu and a wide asymmetric band for Bennu. This leads to the diagnoses of OH-bearing phyllosilicates on Ryugu [6] while H2O- and OH-bearing phyllosilicates on Bennu [5]. A similar absorption band has been observed in laboratory spectra of carbonaceous chondrite meteorites [7, 8]. Separately, the meteorite H content for many of these meteorites was measured by Alexander et al. [9, 10]. Correlations between spectral parameters computed on the hydrated phyllosilicate absorption band of clay minerals and their laboratory-measured water content was found by Milliken et al. [11, 12, 13] and absolute water estimation of Mars regolith was performed by [14]. As described in Praet et al. [15, 16], the normalized optical path length (NOPL) and effective single-scattering albedo (ESPAT) spectral parameters have been applied to estimate the hydrated phyllosilicates water and hydroxyl group hydrogen content (hereafter H content) of each asteroid global average surface. The estimation of the global mean H content of Bennu is 0.71 ± 0.28 wt.% and 0.52 −0.21+0.16 wt.% for Ryugu. In the case of Bennu, the H content surface distribution shows a correlation with the geomorphology with higher values in the high latitudes and lower values in the equatorial band (between –20° and 20° latitudes). Whereas no such correlation is evident in the case of Ryugu as the NOPL and ESPAT parameter computed across its surface do not display any correlation with its surface geomorphological structures. These estimates and spatial trends will be updated as new information is derived from the returned samples (e.g., with enhanced thermal tail removal). The estimated global H content value for Bennu is consistent with the H content range of aqueously altered meteorites such as heated CMs and C2 Tagish Lake, which is in agreement with [5, 16, 18]. As for Ryugu, its global H content is most similar to more strongly heated CMs, which is coherent with the best meteorite analogs for Ryugu near-infrared spectra (thermally metamorphosed CIs and shocked CMs) [6]. Our estimates of phyllosilicate water and hydroxyl group hydrogen content on Bennu and Ryugu, if confirmed by laboratory analysis on both returned samples, will allow the application of the same method to other asteroids, observed from the ground, and from space-telescopes. For asteroids with spectra exhibiting hydrated phyllosilicate absorption bands, such as the ones collected by the AKARI spectral survey [19] for example, estimation of their global mean H content will be possible. The study of water and hydroxyl abundance on primitive asteroids is important for understanding the origin of terrestrial water and to constrain dynamical models and evolutionary processes to better understand the origin and evolution of our Solar System. Acknowledgments We are grateful to the entire OSIRIS-REx Team for making the encounter with Bennu possible. This material is based upon work supported by NASA under Contract NNM10AA11C issued through the New Frontiers Program. We also thank the Hayabusa2 JAXA teams for their efforts in making the mission successful. AP and MAB acknowledge funding support from CNES. References [1] Lauretta D. S. et al. (2017) Space Sci. Rev., 212, 925-984. [2] Tsuda ,Y., Yoshikawa, M., Abe, M., Minamino, H., Nakazawa, S. (2013) Acta Astronaut., 91, 356–362. [3] Reuter, D.C. et al. (2018) Space Sci. Rev., 214, 54. [4] Iwata, T., Kitazato, K., Abe, M., et al. (2017), Space Science Reviews, 208, 317. [5] Hamilton, V.E. et al. (2019) Nature Astron., 3, 332. [6] Kitazato, K. et al. (2019) Science, DOI: 10.1126/science.aav7432. [7] Takir, D. et al. (2013) Meteorit. Planet. Sci., 48, 1618–1637. [8] Takir, D. et al. (2019) Icarus, 333, 243–251. [9] Alexander, C.M.O’D. et al. (2012) Science, 337, 721- 723. [10] Alexander, C.M.O’D. et al. (2013) Geochim. Cosmochim. Acta, 123, 244-260. [11] Milliken, R.E., Mustard J.F. (2005) JGR, 110, E12001. [12] Milliken, R.E., Mustard, J.F. (2007a) Icarus,189(2), 574-588. [13] Milliken, R.E., Mustard, J.F. (2007b) Icarus, 189, 550–573. [14] Milliken, R.E., et al. (2007). J. Geophys. Res. 112, E08S07, doi: 10.1029/2006JE002853. [15] Praet, A. et al. (2021a) Icarus, 363, 114427, doi: 10.1016/j.icarus.2021.114427. [16] Praet, A. et al. (2021b) Astron. Astrophys. doi: 10.1051/0004-6361/202140900. [17] Hamilton, V.E. et al., (2021) Astron. Astrophys. doi: 10.1051/0004-6361/202039728. [18] Hanna, R.D. et al. (2020) Icarus, 346, 113760. [19] Usui, F., Hasegawa, S., Ootsubo, T., Onaka, T. (2019). Publ. Astr. Soc. Japan 71.

. IntroductionThe JAXA Hayabusa2 mission probed the surface of the C-type asteroid (162173) Ryugu both with two touchdown operations to collect samples and return them to Earth, and with remote sensing instruments to characterize it at global scale. Among the payload of the spacecraft, the Near InfraRed Spectrometer (NIRS3) [1] is a point-spectrometer which acquired spectra in the 1.8-3.2 µm range of the asteroid surface to analyse its composition and detect possible heterogeneities. The surface of Ryugu has been shown to be uniformly dark (reflectance factor of 0.017 at 2.0 µm), slightly red-sloped and hydrated due to the presence of a weak, narrow absorption band at 2.72 µm attributed to Mg-phyllosilicates [2]. However, recent studies [3,4] using independent methods of analyses identified minor heterogeneities in the composition on Ryugu.2. Data and methodsHere we continue and expand such studies by selecting NIRS3 datasets that complement the investigated regions of the surface of Ryugu and/or improve the used spatial resolution. The dates corresponding to the datasets retained are the following (sorted by chronological order): July 19th 2018, October 30th 2018, February 28th 2019, July 25th 2019, July 26th 2019, July 27th 2019, October 8th 2019 and October 24th 2019. The coverage of each dataset on Ryugu is displayed in Figure 1. The data used for the analyses have been thermally corrected [2] and photometrically corrected [5].The selected datasets are analysed using the G-mode multivariate statistical approach, using the same technique as in [3]. From a sample of N objects, each expressed by M variables, the code classifies each object in an homogeneous group with no other intervention from the user than the choice of the confidence level (labeled q and expressed in term of σ). The errors on each variable are taken into account in the classification. Further details on the method are available in [3,6].3. Preliminary resultsPreliminary results are shown from the analysis of the October 24th 2019 dataset only, which has the highest spatial resolution among the datasets we selected (7.66-9.67 m/footprint) and which covers the majority (~10°-~80°N) of the Northern hemisphere of Ryugu. Applying the G-mode with a confidence level of 2σ, and only on twenty-four selected wavelengths representative of the asteroid spectral properties, as in [3], we obtain four spectral groups. The mean spectra of each cluster are shown in Figure 2. The distribution of the four groups at the surface of Ryugu is presented in Figure 3.Group #1 contains almost 85% of the spectra, thus corresponding to the average spectral properties of Ryugu. Groups #2 to #4 can be attributed to the compositional heterogeneities. The mean spectra (Figure 2) are mainly separated according to their spectral slope between 2.05 and 2.61 µm. Groups #2 and #4 are the reddest (highest spectral slope), while group #3 is bluer (lower slope) than group #1. We also noted a slight variation for the 2.72 µm absorption band by computing its depth, groups #2 and #4 having the strongest band and group #3 the weakest.The distribution of the four groups on Ryugu (Figure 3) highlights interesting trends. Groups #2 and #4 seem to be concentrated around large craters (e.g. Cendrillon) and large depressions, such as the one located between 230° and 300° in longitude. On the contrary, group #3 appears inside this depression and in the region gathering large boulders between 200° and 230° in longitude.4. Conclusion and perspectivesWe continue and expand previous clustering analyses of NIRS3 data by applying the G-mode algorithm to new datasets, which improve the spatial resolution and/or surface coverage of Ryugu. The preliminary results obtained for the Northern hemisphere of Ryugu are in overall good agreement with the previous findings for the equatorial region [3], confirming the presence of small heterogeneities on the surface. Moreover, they suggest that the material surrounding craters and depressions could present a redder spectral behaviour and a deeper band at 2.7 µm.The G-mode will be applied to all of the selected datasets (Figure 1). Selected regions of interest will also be investigated, notably the second Hayabusa2 touch-down region on which was dropped the Small Carry-on Impactor (SCI) to collect fresh material under the weathered surface [7], by analysing and comparing spectra of the area before and after the impact.AcknowledgementsWe thank the Haybusa2 JAXA team for their efforts in making the mission successful. Hayabusa2 was developed and built under the leadership of JAXA, with contributions from the DLR and the CNES, and in collaboration with NASA, Nagoya University, University of Tokyo, National Astronomical Observatory of Japan, Aizu University, Kobe University, and other universities, institutes, and companies in Japan. We would also wish to thank all the engineers who contributed to the success of the Hayabusa2 mission, especially T. Masuda, S. Yasuda, K. Matsushima, and T. Ohshima. We acknowledge financial support from ASI contract No. 2018-27-HH.0 “Partecipazione alla fase E della Missione Hayabusa2”. We also acknowledge funding from the European Union’s Horizon 2020 research and innovation programme under grant agreement No. 870403. ED and JDPD thanks the financial support of the Agenzia Spaziale Italiana (ASI, contract No. 2017-37-H.0 CUP F82F17000630005). MA Barucci and M Fulchignoni acknowledge financial support by CNES.References[1] Iwata, T, et al.: NIRS3: The Near Infrared Spectrometer on Hayabusa2, Space Sci. Rev., 208, 317-337, 2017.[2] Kitazato, K, et al.: The surface composition of asteroid 162173 Ryugu from Hayabusa2 near-infrared spectroscopy, Science, 364, 272-275, 2019.[3] Barucci, M. A., et al.: Multivariable statistical analysis of spectrophotometry and spectra of (162173) Ryugu as observed by JAXA Hayabusa2 mission, A&A, 629, 2019.[4] Matsuoka, M, et al.: Clustering analysis of NIRS3 infrared spectral data of Ryugu, 51st LPSC, LPI Contribution No. 2326, 2020.[5] Matsuoka, M, et al. (in preparation)[6] Gavrishin, A. I., et al.: Multivariate classification methods in planetary sciences, Earth, Moon and Planets, 59, 141-152, 1992.[7] Arakawa, M, et al.: An artificial impact on the asteroid (162173) Ryugu formed a crater in the gravity-dominated regime, Science, 368, 67-71, 2020.

Aims . This study aims to analyze Phobos’ photometric properties using Mars Express mission observations to support the Martian Moons exploration mission (MMX) devoted to the investigation of the Martian system and to the return of Phobos samples. Methods . We analyzed resolved images of Phobos acquired between 2004 and 2022 by the High Resolution Stereo Camera (HRSC) on board the Mars Express spacecraft at a resolution ranging from ~30 m px −1 to 330 m px −1 . We used data acquired with the blue, green, red, and IR filters of HRSC and the panchromatic data of the Super Resolution Channel (SRC). The SRC data are unique because they cover small phase angles (0.2–10°), permitting the investigation of the Phobos opposition effect. We simulated illumination and geometric conditions for the different observations using the Marx Express and the camera spice kernels provided by the HRSC team. We performed photometric analysis using the Hapke model for both integrated and disk-resolved data. Results . The Phobos phase function is characterized by a strong opposition effect due to shadow hiding, with an amplitude and a half-width of the opposition surge of 2.28±0.03 and 0.0573±0.0001, respectively. Overall, the surface of Phobos is dark, with a geometric albedo of 6.8% in the green filter and backscattering. Its single-scattering albedo (SSA) value (7.2% in the green filter) is much higher than what has been found for primitive asteroids and cometary nuclei and is close to the values reported in the literature for Ceres. We also found a surface porosity of 87%, indicating the presence of a thick dust mantle or of fractal aggregates on the top surface. The SSA maps revealed high reflectance variability, with the blue unit area in the northeast Stickney rim being up to 65% brighter than average, while the Stickney floor is among the darkest regions, with reflectance 10 to 20% lower than average. Photometric modeling of the regions of interest selected in the red and blue units indicates that red unit terrains have a stronger opposition effect and a smaller SSA value than the blue ones, but they have similar porosity and backscattering properties. Conclusions . The HRSC data provide a unique investigation of the Phobos phase function and opposition surge, which is valuable information for the MMX observational planning. The Phobos opposition surge, surface porosity, phase integral, and spectral slope are very similar to the values observed for the comet 67P and for Jupiter family comets in general. Based on these similarities, we formulate a hypothesis that the Mars satellites might be the results of a binary or bilobated comet captured by Mars.

MIRS is part of the French contribution to the Martian Moons eXploration (MMX) mission that will be launched in 2024 by the Japan Aerospace Exploration Agency (JAXA). It is a near-infrared imaging spectrometer devel-oped by the French Laboratory of Space Studies and Astrophysics Instrumentation (LESIA), of the Observatoire de Paris - PSL, with close cooperation and financial support from CNES. One of the major mission goals is to understand the origin of Phobos and Deimos, providing important insights into planetary formation and the transfer of matter in the region connecting the inner and outer solar system. During the four years of the mission, the MIRS control centre will provide precise sequencing of MIRS ac-tivities and guidance of its line of sight, with two main drivers: optimize scientific return and comply with the operability constraints of the instrument, the satellite and the system. In this perspective, observation strategies are designed, modelled and tested iteratively throughout all preparation phases of the mission. Discussions on concrete simulation results and illustrations improve mutual understanding, raise unexpressed needs and con-straints and promote feedback on the efficiency of the proposed strategies. They also favour a global optimization of the entire system with the refinement of the trajectories and of the scheduling considering the seasons of the Martian system. This paper describes the whole process of observation strategies development in cooperation with the MMX and MIRS system and scientific teams, as well as the current status and results.

Identification of water in our Solar System is a key point to understanding the formation and evolution of planetary bodies as well as for astrobiological studies. Scientists identified hydrated minerals as a prime source of H2O in our Solar System. Minerals such as clays, serpentines and other phyllosilicates were discovered by orbiter and lander spacecraft and ground observations on a large variety of rocky surfaces from Mars to small asteroids using InfraRed (IR) spectroscopy as primary technique. It has already been observed that in the presence of large amounts of hydrated minerals in mixtures with anhydrous minerals, the IR spectra can be dominated by the features of hydrated minerals. However, it is still poorly studied how the IR spectra change in presence of different grain size of the two components.The goal of this study was to investigate the infrared spectroscopic features of anhydrous mineral spectra in presence of low amounts of small grain size hydrated hyperfine particles. We prepared several mixtures using 1 wt% and 5 wt% of very small grain size (< 10 mu m) hydrated minerals and 95 wt% and 99 wt% of larger grain size (200-500 mu m) anhydrous minerals. We measured the IR reflectance spectrum of these mixtures in the range 8000-400 cm-1 (1.25-25 mu m). Results presented here show how the presence of a very limited amount of hy-drated minerals with grain size one order of magnitude smaller than the anhydrous component is sufficient to change the IR spectrum, especially in the Near-InfraRed (NIR) region where some of the major hydrated features manifest. On the contrary, the Mid-InfraRed (MIR) part of the spectrum (also identified as thermal infrared) is definitely less affected and anhydrous mineral features continue to be dominant with slight modifications. This result is of pivotal importance for correctly interpreting the IR reflectance observations of planetary bodies such as Mars or asteroids where a mixing of anhydrous and hydrated minerals can be observed. The presence of strong spectroscopic features due to hydrated minerals can be misinterpreted as a large abundance of this material instead of a spectroscopic effect.

ABSTRACT We present new results of the observing program which is a part of the NEOROCKS project aimed to improve knowledge on physical properties of near-Earth Objects (NEOs) for planetary defense. Photometric observations were performed using the 1.2-m telescope at the Haute-Provence observatory (France) in the BVRI filters of the Johnson–Cousins photometric systems between June 2021 and April 2022. We obtained new surface colours for 42 NEOs. Based on the measured colours, we classified 20 objects as S-complex, nine as C-complex, nine as X-complex, two as D-type, one object as V-type, and one object remained unclassified. For all the observed objects, we estimated their absolute magnitudes and diameters. Combining these new observations with the previously acquired data within the NEOROCKS project extended our data set to 93 objects. The majority of objects in the data set with diameters D < 500 m belongs to a group of silicate bodies, which could be related to observational bias. Based on MOID and ΔV values we selected 14 objects that could be accessible by a spacecraft. Notably, we find D-type asteroid (163014) 2001 UA5 and A-type asteroid 2017 SE19 to be of particular interest as possible space mission targets.

ABSTRACT Phobos is the target of the Martian Moons eXploration (MMX), the next sample return mission of the Japanese space agency (JAXA). The mission will investigate the origin of Phobos and Deimos – the two martian moons, using a suite of dedicated instruments. Infrared analysis of the surface composition will be performed by the MIRS spectrometer onboard MMX. Within the scientific studies performed in preparation for the mission, we developed a new laboratory spectral simulant that well reproduces the red and featureless spectrum of Phobos. Our results show that a visible and near-infrared simulant can be developed using dark, opaque materials such as anthracite and coal to reduce the reflectance and absorption features. To investigate the reliability of our proposed simulant in terms of composition and mineralogy, we discussed the similarities and differences in the mid-infrared (MIR) range between our laboratory simulant and some past observations acquired on Phobos. Spectra with different observation geometries were also acquired for our simulant, which give information about grain size and textures of the surface. The simulant developed in our study presents a better match for the Phobos spectrum in the visible and near-infrared compared to the previously proposed simulants.

ABSTRACT The OSIRIS-REx spacecraft completed the first part of the primary objective by successfully sampling the surface of asteroid (101955) Bennu and storing the acquired sample in the re-entry capsule. The sampling ‘Touch-And-Go’ (TAG) maneuver was performed nominally at the primary sampling site, Nightingale, in Bennu’s Northern hemisphere. As a consequence of the TAG, material at the sampling site was mobilized and the morphology of the area was altered. This event offered a unique opportunity to investigate, in detail, the subsurface of asteroid Bennu giving access to fine grained and less altered material from Nightingale crater. We performed a detailed study on the infrared spectrum in the Nightingale region to search for modification resulting from the sampling event by analysing different features: slope, the H2O–OH− related absorption band in the $2.7\ \mu {\rm m}$ region, and other possible features. Our results show that, despite visible alteration of the TAG location detected by cameras, no strong variations are observed in the near-infrared bands and their quantitative evaluation is not possible beyond all the instrumental effects, although some changes may have occurred. We confirm that the infrared spectrum of the sampling site becomes redder with respect to the pre-TAG observations, conceivably due to fine material mobilization and exposure of less altered material, as confirmed by decreased spectral convexity. We identify possible modification of hydrated band at $2.7\ \mu {\rm m}$ but with some concerns due to data quality. However, our results place new constraints on the nature of Bennu’s subsurface material and the sample collected by OSIRIS-REx.

This paper summarizes the evidence for the optical effects of space weathering, as well as the properties of the surface that control optical changes, on asteroid (101955) Bennu. First, we set the stage by briefly reviewing what was known about space weathering of low-albedo materials from telescopic surveys, laboratory simulations, and sample return analysis. We then look at the evidence for the nature of space weathering on Bennu from recent spacecraft imaging and spectroscopy observations, including the visible to near-infrared and thermal infrared wavelengths, followed by other measurements such as normal albedo measurements from LIDAR scans. We synthesize these different lines of evidence in an effort to describe a general model of space weathering processes and resulting color effects on dark C-complex asteroids, with hypotheses that can be tested by analyzing samples returned by the mission.A working hypothesis that synthesizes findings thus far is that the optical effects of maturation in the space environment depend on the level of hydration of the silicate/phyllosilicate substrate. Subsequent variations in color depend on surface processes and exposure age. On strongly hydrated Bennu, in color imaging data, very young craters are darker and redder than their surroundings (more positive spectral slope in the wavelength range 0.4-0.7 mu m) as a result of their smaller particle sizes and/or fresh exposures of organics by impacts. Solar wind, dehydration, or migration of fines may cause intermediate-age surfaces to appear bluer than the very young craters. Exposed surfaces evolve toward Bennu's moderately blue global average spectral slope. However, in spectroscopic and LIDAR data, the equator, the oldest surface on Bennu, is darker and redder (wavelength range 0.55-2.0 mu m) than average and has shallower absorption bands, possibly due to dehydration and/or nanophase and/or microphase opaque production.Bennu is a rubble pile with an active surface, making age relationships, which are critical for determining space weathering signals, difficult to locate and quantify. Hence, the full story ultimately awaits analyses of the Bennu samples that will soon be delivered to Earth.

In this work, we aim to investigate the presence of absorption bands around 3.4 mu m in the infrared spectra of primitive asteroids. We collected the published reflectance spectra of low-albedo asteroids from the literature and analysed the 2.4-3.8 mu m region using the same techniques. From the initial data set of 92 asteroids, we restricted our analysis to 42 spectra of low-albedo asteroids with a good signal-to-noise (S/N) ratio, and we found the absorption feature around 3.4 mu m in the spectra of 16 objects. For objects that are classified by the 3 mu m band into the 'rounded', Ceres-like, and Europa-like groups, the depth of the 3.4 mu m feature is strongly correlated with that of the 3 mu m band. The majority of objects in our data set not showing the 3.4 mu m absorption band have lower S/N spectra and belong to Ch or Chg classes, while asteroids with a detected 3.4 mu m bands mostly belong to C, B, and also P types. Additionally, asteroids with a detected 3.4 mu m band tend to have a lower albedo, redder J-K colours, and more neutral U-V colours. We observe that the analysed objects larger than similar to 300 km in diameter show features due to carbon-bearing materials, which could be explained by their higher S/N ratio in our data set. Finally, we found that the distributions of asteroids showing the 3.4 mu m feature appear to be shifted towards larger distances from the Sun compared to those not showing this band.

Asteroids, and more globally small bodies, are keys to unravel the origin and the evolution of our Solar system. Remnants of the material which formed planets early on, they captured the composition and the conditions of formation of the latter at that time, since they did not undergo too harsh internal alteration during their lifetimes. The Hayabusa2 spacecraft explored the Cb-type asteroid (162173) Ryugu between June 2018 and November 2019, notably collecting data with its Near-InfraRed Spectrometer (NIRS3) in the 1.8-3.2 mu m range. We selected five NIRS3 datasets among the ones having the highest spatial resolution on which we applied the G-mode multivariate statistical analysis, in order to spot small heterogeneities at the surface of Ryugu. Both global scale and local scale cases were investigated. With a confidence level of 30, we obtained two classes at global and local scales, while decreasing to 20 results in the identification of more classes (five at global scale, four at local scale). Overall, our results are consistent among them and with previous studies. In particular, terrains spectrally redder as well as terrains spectrally bluer than the average surface are newly identified by our analysis. The floors of all main craters at the surface of Ryugu appear redder than their surroundings, and are associated with a probable smaller grain size material. A large depression of the Northern hemisphere may contain bluer heterogeneities likely due to a more packed or/and fresher, subsequently deposited material. Finally, a comparison with data from the Hayabusa2 optical camera ONC-T shows no evident correlation between the spectral properties in the near -infrared and in the visible.

ABSTRACT Phobos and Deimos, the two satellites of Mars, were largely studied in the past using ground-based telescope and spacecraft data, although most of the data were obtained by opportunity observations performed by Mars dedicated orbiters. Despite the data available so far, the main composition of the two moons is not yet fully understood. The possible presence of hydrated minerals along with mafic minerals olivine and pyroxene seems to be the most plausible interpretation, but more investigations are needed. MIRS spectrometer on-board the future JAXA MMX sample return mission will help to unveil the open question on the composition of Phobos and Deimos. In this work, we review past spectroscopic observations of the Martian moons, both from ground observatories and spacecraft data set, aiming at better understanding the constraints in interpreting the Mars satellites composition and at identifying the best spectroscopic analogues. We also present new laboratory measurements on mineral mixing and meteorites to match the satellites spectral behaviour. New measurements were acquired at INAF-Astrophysical Observatory of Arcetri and IPAG laboratories at room conditions exploring different geometries and the results obtained set new constraints for future laboratory measurements. Our preliminary results confirm that the surface of Phobos and Deimos can be associated with samples characterized by a higher presence of dark components (e.g. amorphous carbon) or minerals produced by space weathering (e.g. Fe0 and FeS-bearing materials). Presence of dark component could also be totally responsible for the reduced hydrated band observed on the moons without invoking dehydration or OH-implantation on anhydrous surface.

The knowledge of even some basic physical properties of a NEO such as the composition and the internal structure has strong implications for both science and impact mitigation. Depending on its composition and internal structure a meter-size object can completely burn in the atmosphere or reach the ground excavating an impact crater. To date, only 20% of the known NEO population has been characterized. The percentage rises 30% when considering only objects larger than 1 km. The reason is that physical characterization requires availability of large aperture telescopes, accurate ephemerides, and can be performed only if the object is sufficiently bright.International efforts devoted to NEO physical characterization have undoubtedly succeeded in the last decade in addressing this problem through the organization of extensive observational campaigns within the framework of international cooperative programs. Yet the observational work and the associated modelling and simulation research is far from being exhausted in particular as far as the physical characterization of PHOs and smaller objects (D<140 m) passing close or colliding with the Earth are concerned.The aim of the NEOROCKS project is to look at the 2020 horizon and beyond, by proposing an innovative approach that takes into consideration the incoming operations of the next generation sky surveys (with wide-field high-sensitivity telescopes), which will dramatically change the NEO discovery scenario.The ProjectNEOROCKS utilizes an innovative approach focused on: * a) performing high-quality physical observations and related data reduction processes; * b) investigating the strong relationship between the orbit determination of newly discovered objects and the quick execution of follow-up observations in order to face the threat posed by the “imminent impactors”; * c) profiting of the European industrial expertise in on-going Space Situational Awareness initiatives to plan and execute breakthrough experiments foreseeing the remote tasking of highly automatized robotic telescopes, in order to provide a proof-of-concept rapid-response system; * d) guarantee extremely high standards in the data dissemination through the involvement at agency level of a data center facility already operating in a European and international context.The key issue, which marks the radical difference of this approach, is the early onset (from discovery) of a direct link between orbital and physical characterization. Our process continuously analyses the new published detections, in order to find out those which deserve attention as potentially hazardous. For each object identified, the astrometric follow-up and the associated orbit improvements are activated in closed loop until the accuracy of the ephemerides enables successful attempts of observations devoted to physical characterization. Speeding up this process, to complete it within the typical period of visibility of a newly discovered object in the vicinity of our planet (days to weeks), provides an innovative pre-operational scenario for addressing the “imminent impactors” threat. This is particularly relevant since small objects in route of collision with the Earth are likely to be routinely discovered by the new generation NEO sky surveys. Therefore, our approach aims to introduce an entirely new methodology into future operational NEO hazard monitoring systems.The introduction of novel methods for orbit determination and for the prioritization of follow-up observations are at the core of our approach. To assess performances that it can reach, a real-time telescope tasking experiment is envisaged as a test case scenario with the potential to scale up to a global level.Observation campaigns focussed on already known objects and the associated data reduction and analysis are also performed throughout the project, in order to provide high-quality data on specific interesting targets for science and mitigation. This goal is achieved thanks to the participation of astronomical institutions and observatories that can access top-class instrumentation (e.g. 3-10m aperture telescopes) and to perform challenging radar observations within the framework of international collaborations.NEOROCKS also sets up necessary infrastructure to store, maintain and disseminate data produced and tools developed, well beyond the nominal lifetime of the project, thus granting the continuation of its approach and the update of its results. This is achieved through partnership with ASI Space Science Data Centre (SSDC https://www.ssdc.asi.it/), which is equipped with necessary HW/SW environment.Team and activitiesThe main subject of NEOROCKS is to boost the NEO follow-up observations scenario devoted to determine the parameters characterizing asteroid properties, such as composition, shape, spin and mass: these quantities are relevant for our understanding of the nature of NEOs and the potential hazard they pose to human beings.Another fundamental activity is focused in orbit determination and data management: special attention will be given to the timely detection and characterization of small potential imminent impactors of the Earth, which are likely to represent the next real threat.Fig. 1 shows the Work Package Breakdown and Fig. 2 the Work Logic.