On 27 December 2024, near-Earth object (NEO) 2024 YR_4 was discovered by the ATLAS survey and identified as a virtual impactor. A few weeks later, it eventually reached level 3 on the Torino Scale and was the first and only asteroid to be ever classified at that level. Here we report an intensive observational campaign combining time-series photometry in the visible, broadband visible and near-infrared colors, and low-resolution visible reflectance spectroscopy to assess its physical properties. Fourier analysis of the lightcurves yields a synodic rotation period of P = 19.46341 ± 0.00008 min, placing 2024 YR_4 among the fast rotators, even if such rotation is common for objects of similar H magnitude. Its visible and near-infrared colors and spectra are most consistent with an Sq or K taxonomic classification, though some ambiguity remains. Finally, its phase curve exhibits a notably shallow slope (G = 0.51 ± 0.11), from which we derive an absolute magnitude of H_R = 23.82±0.09 mag. After color correction and taking into account other models for the phase function, we report an absolute magnitude of H_V = 24.14±0.25 mag. These characterizations, rotation period, taxonomy, and surface properties, would have been crucial for risk assessment and mitigation planning had the initially high impact probability scenario been confirmed, underscoring the importance for planetary defense of a rapid, coordinated international response.

In July 2025 the third known member of the Interstellar Objects (ISOs) class, 3I/ATLAS, was discovered on its inbound orbital branch, at a heliocentric distance rh = 4.5 au. An intense world-wide campaign started immediately after the discovery and continued up to a few weeks before its perihelion passage. It was possible to depict a scenario of a cometary body redder than most of the Solar System comets, with a deep and narrow negative polarization branch, and a CO2-dominated coma. While approaching its perihelion, a rapid rise in comet’s brightness and a steep heliocentric-distance scaling for the production rates of Ni and CN were observed [1] [2] [3] [4] [5] [6] [7].Due to reciprocal positions of comet and Earth, ground-based observations through the perihelion passage (2025 October 29) were unfortunately impossible, but instead the JUICE spacecraft [8], on its cruise phase towards the Jovian system, was very well placed to observe 3I/ATLAS during those days. Therefore, an observational campaign has been designed and planned, involving several instruments onboard the spacecraft, including the JANUS visible camera [9].123 JANUS images were obtained in 5 observing slots on 2025 November 5, 6, 12, 19, and 25, using 7 filters to cover the spectral range from 340 to 1080 nm. Figure 1 shows an example of image sequence in the F01 (panchromatic) filter obtained from November 5 to November 25, while the comet’s distance from the Sun varied from 1.39 to 1.67 au and the JUICE’s distance from the comet varied from 64 to 188 million km.In this work, the JANUS images of 3I/ATLAS and the first results of the JANUS observing campaign will be presented and discussed.References: [1] Seligman D.Z., Micheli M., Farnocchia D. et al., ApJL 2025. 989, L36-L46. [2] Opitom C., Snodgrass C., Jehin E. et al., MNRAS 2025, 544, 1, L31-L36. [3] Gray Z., Bagnulo S., Borisov G. et al., ApJL 2025, 992, 2, L29-L37. [4] Cordiner M.A., Roth N.X., Kelley M.S.P. et al., ApJL 2025, 991, 2, L43-L52. [5] Rahatgaonkar R., Carvajal J.P., Puzia T.H. et al., ApJL 2025, 995, 1, L34-L46. [6] Hoogendam W.B., Shappee B.J., Wray J.J. et al., 10.48550/arXiv.2510.11779. [7] Lazzarin M., Mura A.C., La Forgia F. et al., ApJL 2026, 998, 1, L30-L35. [8] Grousset O., Dougherty M.K., Coustenis A. et al., PSS 2013, 78, 1-2. [9] Palumbo P., Roatsch T., Lara L.M. et al., SSR 221, 3, id.32

The Asteroid Nodal Intersection Multiple Encounters (ANIME) mission aims to explore three near-Earth asteroids through an innovative 12-unit CubeSat spacecraft, developed under the Italian Space Agency Alcor small satellites program. The mission successfully completed an 8-month Phase A study in 2024, confirming its feasibility. ANIME’s baseline mission profile includes flybys with two Potentially Hazardous Asteroids and a rendezvous with the 40-meter-sized 2000 SG344, an object of high interest for both scientific and planetary defense considerations. The mission’s scientific objectives focus on characterizing the physical properties of these unexplored decameter-scale bodies, including internal structure, rotation state, and surface geology, which are crucial for understanding planetesimal accretion. The collected data will also enable precise orbital determination and impact solution refinement useful for planetary defense. The scientific (commercial) payload comprises a primary panchromatic optical instrument and a secondary three-band optical instrument for imaging, complemented by an X-band transponder for radio science investigations. The key results of the feasibility study are presented, covering system architecture, interplanetary trajectory design, scientific return, and operational concepts. A launch window in the 2029-2033 timeframe was considered during the study. These results highlight ANIME’s capability for addressing fundamental questions in asteroid science and planetary defense.

We report ejecta mass estimates produced by the Double Asteroid Redirection Test impact with Dimorphos, the secondary of the Didymos asteroid binary system. This first demonstration of an asteroid deflection technique was witnessed by the Light Italian Cubesat for Imaging of Asteroids (LICIACube). The LICIACube Unit Key Explorer (LUKE) RGB camera images are used to estimate the ejecta mass, critical to understanding the impact conditions and physical properties of the asteroid. This requires realistic scattering properties for the ejecta particles, which were obtained from model and laboratory scattering analog particles (sizes <1 mu m to similar to 1 cm). The particle size distribution (PSD) of ejecta is constrained from a series of 18 images acquired at widely separated phase angles (50 .degrees 6 to 110 .degrees 2) using the size dependence of the analog scattering phase functions. Total plume radiance in the LUKE RGB channels is determined by spatially integrating over the field of view in each image. Plume radiances are then used to retrieve ejecta mass assuming an optically thin plume, giving lower limit estimates of 0.85 to 1.19 x 10(7) kg. Results indicate that the PSD of ejecta in the nascent plume follows a single power-law coefficient (k approximate to -2.5), rather than the broken power law inferred from later observations. Using a single, high signal-to-noise image, the observed areal mass-brightness relation is extrapolated inward, yielding an increase of approximate to 77% for ejecta mass in the optically thick inner region. Our ejecta mass estimates are consistent with Dimorphos having weak cohesive strength (<5000 Pa but more likely similar to 50 Pa).

Kinetic deflection is a planetary defense technique delivering spacecraft momentum to a small body to deviate its course from Earth. The deflection efficiency depends on the impactor and target. Among them, the contribution of global curvature was poorly understood. The ejecta plume created by NASA's Double Asteroid Redirection Test impact on its target asteroid, Dimorphos, exhibited an elliptical shape almost aligned along its north-south direction. Here, we identify that this elliptical ejecta plume resulted from the target's curvature, reducing the momentum transfer to 44 ± 10% along the orbit track compared to an equivalent impact on a flat target. We also find lower kinetic deflection of impacts on smaller near-Earth objects due to higher curvature. A solution to mitigate low deflection efficiency is to apply multiple low-energy impactors rather than a single high-energy impactor. Rapid reconnaissance to acquire a target's properties before deflection enables determining the proper locations and timing of impacts.

On 2022 September 26, the Double Asteroid Redirection Test (DART) spacecraft intentionally collided with Dimorphos, the moon of the binary asteroid system 65803 Didymos. This collision provided the first full-scale test of a kinetic impactor for planetary defense. Images from DART's DRACO camera revealed Dimorphos to be an oblate spheroid covered in boulders of varying sizes and shapes. Very little was known about Dimorphos prior to DART's impact, including its shape, structure, and material properties. Approach observations and those following the DART impact have provided crucial knowledge that narrows the parameter space relevant to modeling the impact into Dimorphos. Here we present the results of a suite of hydrocode simulations of the DART impact on Dimorphos. Despite remaining uncertainties, initial models of DART's kinetic impact provide important information about the results of DART (e.g., potential crater size and morphology, ejecta mass) and the properties of Dimorphos. Simulations here suggest that Dimorphos has near-surface strength ranging from a few Pascals to tens of kPa, which corresponds to crater sizes of similar to 40-60 m. Simulated crater sizes provide a crucial comparison metric for the European Space Agency Hera mission when it arrives at the Didymos system. Hera's measurement of crater size in combination with measurement of Dimorphos's mass will allow us to assess our simulations and provide the information needed to make the DART impact experiment both the first test of a planetary defense mitigation mission and the first full-scale planetary defense simulation validation exercise.

Context. After a successful sample-return mission to the asteroid (162173) Ryugu, the Hayabusa2 spacecraft is currently on its way to encounter two near-Earth asteroids: (98943) Torifune (formerly known as 2001 CC21) and 1998 KY26. Aims. In this article, we study the asteroid (98943) Torifune, the first object that is to be visited by the spacecraft during its extended mission. To prepare for its encounter with the spacecraft, it is crucial to study this object from Earth. We conducted several ground-based observations to characterize this asteroid and understand its mineralogy. Methods. In January and February 2023, we carried out spectroscopic and photometric observations at the 2.56 m Nordic Optical Telescope, in the visible and near-infrared ranges, covering different rotational phases of the asteroid. Results. Based on spectra analysis in the visible and near-infrared ranges, confirmed by the color studies, we determined that Torifune belongs to the Sq-type, according the Bus-DeMeo taxonomy. Assuming this taxonomy and its equivalent diameter (D similar to 465 +/- 15 m), we estimated the mass of this asteroid to be 1.81 +/- 0.11 x 10(11) kg. In term of mineralogy, we found a close match with ordinary L chondrites. Conclusions. As our observations covered almost a complete rotation phase, we did not find any spectral variation at different rotational phases, meaning that there is no substantial heterogeneities on Torifune's surface. We compared the spectral slope of (98943) Torifune with that of the S-complex members of the Lucienne family. However, further studies, especially dynamical ones, are needed to confirm whether this object originates from the Lucienne family.

On 2022 September 26, the Double Asteroid Redirection Test (DART) spacecraft intentionally collided with Dimorphos, the moon of the binary asteroid system 65803 Didymos. This collision provided the first full-scale test of a kinetic impactor for planetary defense. Images from DART’s DRACO camera revealed Dimorphos to be an oblate spheroid covered in boulders of varying sizes and shapes. Very little was known about Dimorphos prior to DART’s impact, including its shape, structure, and material properties. Approach observations and those following the DART impact have provided crucial knowledge that narrows the parameter space relevant to modeling the impact into Dimorphos. Here we present the results of a suite of hydrocode simulations of the DART impact on Dimorphos. Despite remaining uncertainties, initial models of DART’s kinetic impact provide important information about the results of DART (e.g., potential crater size and morphology, ejecta mass) and the properties of Dimorphos. Simulations here suggest that Dimorphos has near-surface strength ranging from a few Pascals to tens of kPa, which corresponds to crater sizes of ∼40–60 m. Simulated crater sizes provide a crucial comparison metric for the European Space Agency Hera mission when it arrives at the Didymos system. Hera’s measurement of crater size in combination with measurement of Dimorphos’s mass will allow us to assess our simulations and provide the information needed to make the DART impact experiment both the first test of a planetary defense mitigation mission and the first full-scale planetary defense simulation validation exercise.

On 26 September 2022 the Double Asteroid Redirection Test (DART) spacecraft collided with Dimorphos, the moon of the near-Earth asteroid 65803 Didymos, in a full-scale demonstration of a kinetic impactor concept. The companion LICIACube spacecraft documented the aftermath, capturing images of the expansion and evolution of the ejecta from 29 to 243 s after the impact. We present results from our analyses of these observations, including an improved reduction of the data and new absolute calibration, an updated LICIACube trajectory, and a detailed description of the events and phenomena that were recorded throughout the flyby. One notable aspect of the ejecta was the existence of clusters of boulders, up to 3.6 m in radius, that were ejected at speeds up to 52 m/s. Our analysis of the spatial distribution of 104 of these boulders suggests that they are likely the remnants of larger boulders shattered by the DART spacecraft in the first stages of the impact. The amount of momentum contained in these boulders is more than 3 times that of the DART spacecraft, and it is directed primarily to the south, almost perpendicular to the DART trajectory. Recoil of Dimorphos from the ejection of these boulders has the potential to change its orbital plane by up to a degree and to impart a non-principal axis component to its rotation state. Damping timescales for these phenomena are such that the Hera spacecraft, arriving at the system in 2026, should be able to measure these effects.

In the last decade an increasing number of CubeSat-class spacecraft have been involved in the execution of space missions, operating at distances from our home planet ranging between Low-Earth Orbit to Mars. In particular, the Light Italian CubeSat for Imaging of Asteroids (LICIACube) mission of Agenzia Spaziale Italiana (ASI, Italian Space Agency) has contributed to the Double Asteroid Redirection Test (DART) mission of National Aeronautics and Space Administration (NASA) by witnessing, on September 26th, 2022, the successful impact of DART spacecraft with the asteroid (65803) Didymos I Dimorphos, and revealing the immediate aftermaths of the event while performing a quick flyby, successfully participating in the first Planetary Defense real-scale test ever conducted by humanity. LICIACube mission, leveraging on national competences and together with the international collaboration with the DART mission, has been able to improve the operational, technical, managerial and scientific know-how at national level, together with creating new records in interplanetary exploration. The concept of modularity in space segments, for the achievement of ever complex mission goals, has recently found favourable conditions thanks to the increasing capabilities of smaller platforms. In particular, the present work aims also at highlighting and describing the value of the LICIACube contribution in validating and verifying the outcome of the kinetic impact method with the presence of a proximity observer spacecraft.

Introduction The study of near-Earth objects (NEOs) is crucial to better understand the origin, formation and the evolution of the solar system. In particular, compositional, morphological and orbital characterisation of NEOs sheds light on the delivery of water and organics [1,2,3] to the prebiotic Earth, while ironically, some NEOs could be potential hazards for life on Earth [4], as it has been witnessed in the past during impacts. Furthermore, these objects are also of interest for the future of humankind, for they could be useful as vital resources during interplanetary travel. Given this context, we apply the G-mode multivariate statistical clustering method [5,6,7] on the orbital parameters of the currently available NEOs population, to probe potential associations with their spectral classification [8,9,10].Data and methods We apply the G-Mode multivariate statistical clustering analysis to selected orbital elements of NEOs to determine any dynamical clustering of objects. Once the clusters of objects are found, we proceed to investigate whether they have any correlations with spectral classes. The G-mode method leads to an automatic statistical clustering of a sample containing N objects (NEOs in this case), described by M variables (orbital elements) with the only control imposed by the user being the confidence level q1, expressed in terms of σ.Our sample consists of 10669 NEOs belonging to the dynamical groups Atiras, Atens, Apollos and Amors, available from the Minor Planet Center, filtered based on their orbital uncertainty (excluding those with an uncertainty parameter > 4). Our input parameters to the G-mode method are twofold. First, we use three variables: inclination (i), eccentricity (e) and semi-major axis (a) of the orbit as these are the main three parameters that define an orbit around the Sun. Secondly, we include three pseudo-parameters: mean orbital intersection distance with respect to the Earth (eMOID), perihelion distance (q) and aphelion distance (Q) of the orbit, in addition to the aforementioned three parameters, thus using six variables.Preliminary results Using i, e and a of the NEOs in our sample as inputs for G-mode, we obtain three clusters of NEOs at q1=1.9σ (with an accurate classification probability of 94.26%). The mean parameter values of each cluster with the median absolute deviation are given in Table 1. We have also reported some other parameters of interest, which include, Tisserand parameter with respect to Jupiter (TJ) and the absolute magnitude H. At this criterion, the vast majority of objects are clustered in the cluster #1. The cluster #2 with only 20 objects, appears interesting, as it is constrained by low-inclined, quasi-circular Earth-like orbits. The objects of the final cluster #3 are constrained by their relatively larger inclinations. We next used six variables: i, e, a, eMOID, q and Q as inputs for G-mode, while still holding q1 fixed at 1.9σ, in which case six clusters are found as reported in Table 2. Among the reported clusters, clusters #3,4 and 6 are of particular interest, for they could be associated with Jupiter-family cometary nuclei (2 < TJ < 3) as per their Tisserand parameter with respect to Jupiter. As such, the objects in these three clusters could potentially be extinct cometary nuclei. Interestingly, these clusters also have relatively higher eccentricities. We have checked available taxonomic classifications of NEOs [11,12,13] in the literature to get an insight into the composition of the objects found in our G-Mode clusters. Although taxonomic classifications are not available for the majority of members in the clusters, we find that (i) cluster #3 contains 4 C-type objects, (ii) cluster #4 contains 1 C-type, 2 D-type, 1 L-type, 5 S-type and 1 X-type objects, (iii) cluster #5 contains 1 B-type, 1 C-type, 1 T-type and 1 X-type objects. Apart from the S-type objects, the others usually have dark and red spectra indicative of primitive origin, which does not reject a cometary composition. We will augment this on-going study with more data and final results will be presented and discussed. Acknowledgements We acknowledge the financial support from Agenzia Spaziale Italiana (ASI, contract No. 2017-37-H.0 CUP F82F17000630005). We also acknowledge funding from the European Union’s Horizon 2020 research and innovation programme under grant agreement No. 870403.References[1] Marty, B., Guillaume, A. et al. 2016, Earth and Planetary Science Letters, Volume 441, Pages 91-102[2] Altwegg, K, Balsiger, H, Bar-Nun, A. et al. 2015, Science, Vol. 347, Issue 6220, 1261952[3] Ehrenfreund, P. & Sephton 2006, Faraday Discuss., The Royal Society of Chemistry, 133, 277-288[4]Perna, D., Barucci M. A., Fulchignoni M. 2013, Astronomy and Astrophysics Review, Vol. 21,65[5] Barucci, M.A., Capria, M.T., Coradini, A. et al. 1987, Icarus 72, 304[6] Gavrishin, A. I., et al. 1992, Earth, Moon and Planets, 59, 141-152 [7] Barucci, M.A., Belskaya, I., Fulchignoni, M. et al. 2005, AJ 130, 1291[8] Bus, S. J., & Binzel, R.P. 2002, Icarus 158, 146[9] DeMeo, F. E., Binzel, R. P., Slivan, S. M. & Bus, S. J. 2009, Icarus, 202, 160-180[10] DeMeo, F. E., Alexander, C. M. O., Walsh, K. J.et al. 2015, Asteroids IV, 13-41[11] Perna, D., Barucci, M.A. et al. 2018, Planetary and Space Science, 157, 82-95[12]Devogèle, M., Moskovitz, N. et al. 2019, The Astronomical Journal, American Astronomical Society, 158, 196[13] Ieva, S., Dotto, E. et al. 2020, A&A, 644, A23

IntroductionThe NASA Double Asteroid Redirection Test (DART) mission will be the first test to check an asteroid deflection by a kinetic impactor. The target of DART mission is Dimorphos the secondary element of the (65803) Didymos binary asteroid system, and the impact is expected in late September – early October, 2022 [1] The DART S/C will carry a 6U cubesat called LICIACube (Light Italian Cubesat for Imaging of Asteroid) [2], provided by the Italian Space Agency, with the aim to collect pictures of the impact’s effects. On board LICIAcube will be hosted 2 camera payloads: LEIA a panchromatic (400-900nm Filter, 2.9x2.9° FOV) Narrow Angle Camera and LUKE a RGB (Bayer color filter, 4.8 x 9.15° FOV). LICIACube will be able to acquire the structure and evolution of the DART impact ejecta plume and will obtain high-resolution images and 2 colours data (B-G, G-R) of the surfaces of both bodies and the plume.In order to check the imaging capability and to optimize the fast scientific phase of LICIACube, the LICIACube team performed simulations of pictures’ acquisition. In these simulations, considering the specifications of the 2 optical payloads and the foreseen mission design, we reconstructed synthetic images mainly of the plume. Since the study of the plume and its evolution is one of the main scientific goal of the mission we performed a scattering modelling of the ejecta in order to invert the future photometric data deriving hints on the intimate nature of the dust particles released by the impact.Plume simulated Images and column densityWith the two-fold aim of set the operative parameters for the Payloads and to understand the information retrievable by the images of the evolving plume we started an imaging simulation activities taking into account:LICIAcube mission design [3] (Trajectory, Speed, illumination conditions) Payloads optical characteristics The plume evolution was simplified assuming:Non colliding particles during the plume evolution; A speed distribution in the plume given by eq: Where x is the distance on Dimorphos surface from the DART impact point and the other parameters used, considering as main material of asteroid system the cemented basalt, are reported in table:We considered the most representative 3 size bins for what concerns the ejected mass, the expected total number of particles are reported in table:In Figure 1 is reported the simulated image obtained considering the LICIACube trajectory 50s before the close approach (about 110 s after the DART impact).Figure 1 Plume simulated image relative values for irradianceOnce the simulated column density image was obtained, we added a scattering simulation considering spherical dust particles and using a Mie code well suited for large particles approaching the geometric optics regime [4]. In this way we were able to translate column densities in luminous fluxes measured by the instrument using a methodology described in the next section.Plume colours scattering modellingRGB data of the ejecta plume can be used to derive hints on the physical properties of the ejected particles through scattering modelling of the measured two colours (B-G, G-R) and the phase function versus the phase angle of observation α.Given the intensity of solar light incident on the plume’s single particle Iinc,, considering the incident solar light as unpolarized, the intensity of light scattered by the particle at α, Isca is given by [5]:where S11(α) is the first element of the 4X4 scattering Müller matrix, k=2π/λ is the wave number, and r is the distance between the particle and the observer. In this case: being FSun the solar flux at 1 AU, rh the heliocentric distance of the dust particle, and a its radius.The Mie code provides the complete scattering matrix once the dimension of the particle and its composition in terms of the complex refractive index of the material at the considered wavelength are given as input. We used largely referenced laboratory data on basaltic materials to obtain the optical properties of the dust particles [6]. This composition is used to model the dust particles residing on the asteroid surface [1], [2].Then, in order to find the intensity due to the scattering of a single particle measured by the instrument at phase angle α, we convolved Isca with the photometric response of the instrument. For a generic filter, such measured intensity is where Resp is the photometric response of the instrument extended throughout the bandpass of the filter. This response is a known product of several factors as the entrance pupil of the system, the reflectivity of the optics, the transmission curve of the filter, the quantum efficiency of the detector, and the exposure time.Synthetic colours of the dust particles can therefore being computed being the generic color A-B = -2.5log(IA/IB). We performed sample scattering colour calculations varying the particle size from 0.1 micron to 1 cm.Small particles provide extremely variable colours due to the strong influence of scattering resonances being the incident wavelength comparable with the size of the particles themselves. Colours get stable for a larger interval of phase angle proportionally to the increase of the size. Observations of stable colours in the plume during LICIACube flyby will be indicative of particles larger than 100 micron. At the same time, large basalt particles provide a flatter phase function at intermediate and small phase angles than smaller particles.Combined observations of the plume phase function and colour will therefore effectively constrain the size of the ejected particles providing theoretical inputs to the dynamical models.Acknowledgements: The LICIACube team acknowledges financial support from Agenzia Spaziale Italiana (ASI, contract No. 2019-31-HH.0 CUP F84I190012600).References[1] Cheng et al. P&SS 121 (2016).[2] Dotto et al. 2020, " LICIACube - the Light Italian Cubesat for Imaging of Asteroids In support of the NASA DART mission towards asteroid (65803) Didymos” P&SS, submitted.[3] Capannolo et al. 70th IAC Conference Paper (2019).[4] Wolf and Voshchinnikov. Computer Physics Communications 162 (2004).[5] Bohren & Huffman. Absorption and Scattering of Light by Small Particles. Wiley (1983).[6] Pollack et al. Icarus 19 (1973).

Introduction: The NASA Double Asteroid Redirection Test (DART) impact [1], was the first space mission that successfully demonstrated the kinetic impactor technique for planetary defense. It was at the same instant, on 26th September 2022, when ASI/Light Italian Cubesat for Imaging of Asteroids (LICIACube) [2] was the first Cubesat to image the plume coming from Dimorphos, the smaller body of the binary asteroid (65803) Didymos. The DART impact into Dimorphos [3] caused ejecta plume propagation with high velocity and very filamentary structure, composed of dust particles from μm to cm sizes in size [4]. The large aperture and observed spikes did not prevent propagation of larger excavated material, namely, boulders up to ~2 m [5]. Far-field observations such as HST clearly showed dust tail formed from the low-speed ejecta dust due to solar radiation pressure (SRP) [4].The scientific objectives: The estimation of the size distribution and velocity distribution of the plume in close vicinity to Dimorphos, captured in the LICIACube images is still an unanswered question. While the long-term monitoring of the tail can reveal the size distribution up to tens of cm in size, the impact simulations can constrain the initial velocity of the excavated material. Near and mid – field simulations considering different dynamical properties at local scale can address the complex collimated but inhomogeneous distribution of the dust within the plume. Here, we discuss some of the dynamical properties of the plume using the available observational DART and LICIACube data of the plume propagation. We try to constrain the particle sizes within the collimated plume structures.The model: We apply the 3D+t model – LIMARDE [6,7] constrained with laboratory observations [8], impact simulations and near- and far- field observations such as the LICIACube [9] images and HST [2] dust observations, respectively. The model computes single particle trajectories, the dust rotational frequencies and velocity as well as the particle orientation at any time and distance. We compute the dust velocity distribution based on the physical properties (size, mass and shape) derived from the LICIACube observations. The results are useful to check what is the role of the fragmentation of the particles and to constrain the physical properties based on the dynamical properties of the ejected dust in the near- and mid- environment.Fig. 1. The dust speed and rotation frequency of particles with different shapes as constitutes of the dust clumps shown in the observations of ASI/LICIACube/LUKE, 2022-09-26T23:17:04.Discussion: The LICIACube observations suggest that we have the locations of accumulation of different particles along the collimated plume streamers. The latter may contain particles of the same density and shape but with different velocity and rotation due to the initial ejected position and form not-linear motion within the collimated filament – like structures. In Fig. 1 we show LIMARDE simulations with particles of different shapes that result with different velocities suggesting a scenario where the dusty clumps could occur at the same location due to motion of particles with different shapes. The study discusses what is the probability that these dust clumps are formed owing to fragmentation, or their location is a result of their motion history of the ejected particles.Acknowledgements: This research was supported by the Italian Space Agency (ASI) within the LICIACube (ASI-INAF agreement AC n. 2019-31-HH.0).References: [1] Rivkin, A.S. et al. 2021, PSJ, 2, 24pp; [2] Dotto, E. et al. 2021, PSS 199, [3] Daly, R.T. et al. (2023) Nature. [4] Li, J.-Y., et al. (2023) Nature. [5] Farnham et al. LPSC abs. [6] Ivanovski et al. 2023, u.rev.; [7] Fahnestock et al. 2022, PSJ; [8] Ormo et al. 2022, E&PSL [9] Dotto et al. 2023, Nature

The Japan Aerospace Exploration Agency's (JAXA) Hayabusa2 mission, following the successful return of samples of the near-Earth asteroid (NEA, 162173) Ryugu, in December 2020, has been extended to explore two more NEAs. These are (98943) 2001 CC21, which is scheduled for a flyby in 2026, and the fast-spinning 1998 KY26, for a rendez-vous on 2031. The extended mission has been named Hayabusa2#, where the # character stands for "SHARP" (Small Hazardous Asteroid Reconnaissance Probe). Several observing campaigns of these two targets have been and will be carried out to better understand their physical properties in support of the Hayabusa2# mission, and to optimize the observing strategy.In this work we present a new estimate of the size, albedo and rotational period of 2001 CC21. This is based on observations of 2001 CC21 spectral energy distribution in the thermal infrared obtained by NASA’s Spitzer Space Telescope and new ground-based photometric observations carried out at the 3.5m New Technology Telescope of ESO, at the 1.2m Haute Provence Observatory, and at the 0.7m Abastumani telescope. In the optical, we obtained three complete lightcurves in 2023-2024. The Spitzer observations of (98943) 2001 CC21 were obtained on November 20, 2005 from 10:17 to 12:26 UT with the Infrared Spectrograph (IRS). Data were acquired in low resolution mode covering the 5.2-38 micron range in 4 IRS long slit segments. The data were reduced starting from the basic calibrated data generated by the Spitzer Space Center automated pipeline, and the sky background was removed by differencing two consecutive images taken at different nodding positions for each spectral segment. Finally, spectra were extracted using the Spitzer IRS Custom Extraction (SPICE) software. Data were modeled with the Near Earth Asteroid Thermal Model to determine the asteroid size and albedo.From ground-based observations, we determine an absolute magnitude of H=18.94±0.05, and a rotational period of 5.02124±0.00001 hours, with a large lightcurve amplitude of ˜0.8 magnitude at a phase angle of 22o, indicating a very elongated shape with estimated a/b semiaxis ratio > 1.8, or a close-contact binary body. The emissivity of 2001 CC21 is consistent with that of silicates, and its albedo is 21.6+1.1-1.0 %. Finally, the spherical-equivalent diameter of 2001 CC21 is 465±15 m.The albedo value and emissivity here determined, coupled with results from polarimetry and spectroscopy from the literature, confirm that 2001 CC21 is an S-complex asteroid, and not a L-type, as previously suggested. The size of 2001 CC21 is less than 500 m, which is smaller than its first size estimation (˜700 m). These results are relevant in preparation of the observing strategy of 2001 CC21 by Hayabusa2 extended mission.

We spectroscopically characterized the Didymos system, target of the Double Asteroid Redirection Test (DART)/Light Italian Cubesat for Imaging of Asteroids (LICIACube) space mission, close in time to the DART impact event, during six nights between 2022 August and November at Telescopio Nazionale Galileo. Here, we show that near-infrared (NIR) spectra (0.75-2.25 mu m) look mostly similar within the same night and between different nights. They are in good agreement with the only spectrum previously available in the literature, observed almost 20 years before those reported in this paper. During one of the observing nights we also obtain spectroscopy information on the ejecta tail induced by the DART impact. The spectrum of the ejecta tail is also very similar to Didymos/Dimorphos itself. All of these aspects seem to suggest that the Didymos system in the NIR looks mostly homogeneous, with very subtle spectral variations.

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.

Kinetic deflection is a planetary defense technique that delivers spacecraft momentum to a small body to deviate its course from Earth. The deflection efficiency depends strongly on the impactor and target. Among them, the contribution of global curvature was poorly understood. The ejecta plume created by NASA's DART impact on its target asteroid, Dimorphos, exhibited an elliptical shape almost aligned along its north-south direction. Here, we identify that this elliptical ejecta plume resulted from the target’s curvature, reducing the momentum transfer to 44±10% along the orbit track compared to an equivalent impact on a flat target. We also find lower kinetic deflection of impacts on smaller Near-Earth objects (NEOs) due to higher curvature. A solution to mitigate low deflection efficiency is to apply multiple low-energy impactors rather than a single high-energy impactor. Rapid reconnaissance to acquire a target's properties before deflection enables determining the proper locations and timing of impacts.

Spacecraft observations revealed that rocks on carbonaceous asteroids, which constitute the most numerous class by composition, can develop millimeter-to-meter-scale fractures due to thermal stresses. However, signatures of this process on the second-most populous group of asteroids, the S-complex, have been poorly constrained. Here, we report observations of boulders' fractures on Dimorphos, which is the moonlet of the S-complex asteroid (65803) Didymos, the target of NASA's Double Asteroid Redirection Test (DART) planetary defense mission. We show that the size-frequency distribution and orientation of the mapped fractures are consistent with formation through thermal fatigue. The fractures' preferential orientation supports that these have originated in situ on Dimorphos boulders and not on Didymos boulders later transferred to Dimorphos. Based on our model of the fracture propagation, we propose that thermal fatigue on rocks exposed on the surface of S-type asteroids can form shallow, horizontally propagating fractures in much shorter timescales (100 kyr) than in the direction normal to the boulder surface (order of Myrs). The presence of boulder fields affected by thermal fracturing on near-Earth asteroid surfaces may contribute to an enhancement in the ejected mass and momentum from kinetic impactors when deflecting asteroids.

The NASA DART mission impacted the asteroid Dimorphos, the satellite of the asteroid Didymos, at 23:14 UTC on September 26, 2022, as a planetary defense test. This marked the first hypervelocity impact experiment on an asteroid relevant to planetary defense. The Italian Space Agency's LICIACube captured crucial imagery before and after the impact, aiding in studying the ejecta's distribution in inertial space. The data returned by LUKE camera aboard LICIACube thus enabled the characterisation of the orientation and geometry of resultant ejecta [1,2,3], which are closely related to the calculation of how effective the impact has been in imparting momentum to the asteroid (parameter β) [4]. LUKE images acquired at different vantage points with respect to the ejecta, allowed the characterisation of the global ejecta structured in the aforementioned studies, by approximating it to a hollow cone. Nevertheless, the real structure of the ejecta is intricate and contains complex structures. Given the availability of LUKE images, we attempt to recover the three-dimensional structure of the ejecta by coregistering them to a Dimorphos-centred coordinate system. We trace two-dimensional ejecta shapes [5] as projected onto LUKE images and then place these 2D shapes (scaled with distance) along LUKE boresight at different distances to create depth so that we capture all the possible theoretical planes where different parts of ejecta structure could reside (Figure 1). Once we obtain such 3D profiles for four different images obtained at various vantage points, we intersect them in an inertial J2000 space. The material common to all the intersections then provides us with a three dimensional structure that is compatible with the images used as input to trace two dimensional profiles on the LUKE images. Then, we bring the resulting structure back to LUKE image space and visualise them with the original images to see how they compare. Fig.1. Top panel: Left: A perspective view of the three dimensional profile of the ejecta structure recovered using 3 scaled planes (image acquired at '2022-09-26T23:17:03.004' UTC) placed at the location of LICIACube, at the centre of Dimorphos and away from Dimorphos in the same line of sight between LICIACube and Dimorphos. Right: Planes removed to highlight the ejecta structure. Bottom pane: The same for the image acquired at '2022-09-26T23:17:18.000' UTC.In this way we’re able to validate the three dimensional model we obtained by intersecting three dimensional profiles derived from LUKE images. In order to check its accuracy, the model will be cross-checked against the solutions of Deshapriya et al., 2023 and Hirabayashi et al., 2024 which are compatible with each other. The model will later be refined to remove any resulting artifacts. The result of this work will allow us to understand the three dimensional distribution of ejecta material in inertial space and hence will help constrain models of ejecta propagation following planetary impacts. Acknowledgments: This research was funded by the Italian National Astrophysical Institute (INAF) - Call for Fundamental Research 2022. The LICIACube team acknowledges financial support from Agenzia Spaziale Italiana (ASI, contract No. 2019-31-HH.0 CUP F84I190012600). References [1] Dotto et al., Nature, 627, pages 505–509 (2024) [2] Hirabayashi et al., submitted to Nature Communications [3] Deshapriya et al., Planet. Sci. Journal. 4, 231 (2023) [4] Cheng et al., Nature, 616, 457 (2023) [5] Zinzi et al., Planet. Sci. Journal. 5, 103 (2024)

Due to their proximity Near-Earth objects (NEOs) provide us with a unique opportunity to investigate asteroids with diameters down to dozens of meters. Moreover, NEOs create a constant potential hazard to the Earth, and thus the study of their physical properties is crucial for estimating the potential risks. A new photometric survey was carried out in the framework of the NEOROCKS (NEO Rapid Observation, Characterization, and Key Simulations) project funded by the European Union’s Horizon 2020 program with the aim to derive the visible colors of NEOs and perform the initial taxonomic classification.The photometric survey was performed with a use of a 1.2m telescope at the Haute-Provence observatory and a 1.0m telescope at the Pic du Midi observatory, both located in France. Standard broadband Johnson-Cousins and Sloan photometric systems were used.Color indexes were measured for a total of 51 NEOs. Among them, 24 objects belong to a group of potentially hazardous asteroids (PHAs). The majority of objects have absolute magnitude H in a 17-20 mag range.The preliminary taxonomy was done following the classification by [1] using M4AST service [2]. In order to have better statistics only the main taxons S-, C-, and X-complexes, and A-, D-, V-types were considered. Fig. 1 shows color-color diagrams for the observed NEOs. One can see that different classes of objects are concentrated in the different areas of the plots, which suggests that our taxonomic classification is rather reliable. Additionally, our taxonomic classification was confirmed by albedo values that are available for about a third of objects in our sample. About 43% of objects in our sample belong to the S+Q-complex, about 19% to X-complex, 16% to C-complex, 12% were classified as D-types, and, finally, 6% and 4% as A- and V-types, respectively. The found distribution is in a general agreement with the previous works (e.g. [3, 4, 5]).Fig. 1. Color-color diagrams for the objects in our survey showing their classification into the main taxonomic classes. The boxes represent the 1σ deviation from the mean colors for the groups of “carbonaceous” and “silicate” objects.The median values of absolute magnitudes and estimated diameters vary for different groups of objects in our sample: H=18.10±0.95 and D=1219±729 m for low-albedo "carbonaceous" objects, whereas H=19.50±1.20 and D=344±226 m for "silicate" objects. This could be a result of an observational bias towards higher albedo objects. The absolute magnitude versus Minimal Orbital Intersection Distance (MOID) was also derived (Fig. 2). PHAs by almost 65% represented by “silicate” objects, however there are also a few low albedo objects that could be more challenging in terms of mitigation that relies on the porosity of the object (e.g. [6]).Fig. 2. Earth’s MOID vs. absolute magnitude for different groups of NEOs. The line at MOID=0.05 au separates PHAs from the rest of the NEOs. Acknowledgements. This project has received funding from the European Union’s Horizon 2020 research and innovation programme under grant agreement No 870403.References[1] DeMeo, F., Binzel, R., Stephen M. Slivan, S., Bus, S. Icarus, 202, 160, 2009.[2] Popescu, M., Birlan, M., Nedelcu, D. A&A, 544, 130, 2012.[3] Binzel, R. P., DeMeo, F. E., Turtelboom, E. V., et al. Icarus, 324, 41, 2019.[4] Devogèle, M., Moskovitz, N., Thirouin, A., et al. AJ, 158, 196, 2019.[5] Ieva, S., Dotto, E., Mazzotta Epifani, E., et al. A&A, 644, A23, 2020.[6] Perna, D., Barucci, M. A., Fulchignoni, M. The Astronomy and Astrophysics Review, 21, 65, 2013.