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.

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.

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.

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

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

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.

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.

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.

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.

The NASA Double Asteroid Redirection Test (DART) spacecraft impacted the moon Dimorphos of the [65803] Didymos binary system and changed the binary orbit period, demonstrating asteroid deflection by a kinetic impact and indicating that more momentum was transferred to Dimorphos by escaping impact ejecta than was incident with DART. Images of the DART impact ejecta plume were obtained by the Light Italian cubesat for Imaging of Asteroids (LICIACube) in the first few minutes after the DART impact. The ejecta plume imaged by LICIACube 158 s after the DART impact prior to closest approach shows no evidence for plume clearing at low altitude. The ejecta plume imaged 175 s after the DART impact is optically thick up to projected altitudes of 200 m above the surface of Dimorphos. These observations are compared with models of the impact ejecta plume optical depth, structure, and evolution, which are developed from point-source scaling models fitted to numerical simulations of the DART impact into a rubble pile Dimorphos with different material strengths. The observations of the impact plume optical depth and the high momentum transfer from the DART impact are not consistent with impact and ejecta plume models assuming the Dimorphos cohesive strength to be as high as 5000 Pa. Models with 5 and 50 Pa Dimorphos cohesive strength provide the overall best consistency with plume opacity observations and high momentum transfer.

On 2022 September 26, NASA's Double Asteroid Redirection Test (DART) successfully hit Dimorphos, the smaller companion of the binary system formed with the asteroid (65803) Didymos. Both the binary system and the impact event were imaged by the Light Italian Cubesat for Imaging of Asteroids, detached from DART 15 days before the impact. Images from the onboard LUKE red, green, and blue camera together with ground-based observations enabled the reconstruction of Didymos's brightness phase curve, with phase angles ranging from 2.35° to 107.7°. The opposition effect regime was studied using the exponential-linear equation, the “Shevchenko” function and the linear-by-parts model while the IAU-official HG1G2 magnitude system was applied to the full phase curve. The opposition effect indicates an unusual asteroid surface for an S type, with characteristics similar to M-type asteroids. While the HG1G2 parameters from the full phase curve place Didymos well among asteroids of the taxonomic C complex. Didymos’s phase curve parameters when compared to near-Earth asteroids are very close to the Q type (1862) Apollo, indicating possible depletion of fine submicrometric grains through resurfacing. Didymos's geometric albedo (0.15 ± 0.01) is reported to be 30%–45% smaller than the average geometric albedo for near-Earth S types (0.26 ± 0.04). We propose that Didymos might be an LL ordinary chondrite analog containing albedo-suppressing, shock-darkened/impact melt minerals that have undergone resurfacing processes in the past. A comparison with meteorites indicates that, less likely, Didymos could also contain materials analog to carbon-bearing brecciated L3 ordinary chondrites.

IntroductionAsteroid (65803) Didymos is an S-type [1] Apollo binary system characterized by a 780±30 m size primary, called Didymos, and a 164±18 m size secondary, called Dimorphos, orbiting at a distance of ~1.19 km [2]. The primary rotation period is 2.26 h [2], close to the 2.2 h disruption spin barrier [3], while the period of revolution of Dimorphos around the primary is 11.9217+0.0002 h [4]. This asteroid has been selected as the target of the Double Asteroid Redirection Test (DART, [5]), whose main goal is to impact Dimorphos at a speed of 6.6 km/s on September 30, 2022, thereby demonstrating the kinetic impactor technique and evaluating the resulting impulsive deflection.The scientific camera onboard DART is called DRACO, i.e. the Didymos Reconnaissance and Asteroid Camera for Op-nav [6]: its main goals are to image Didymos for optical navigation, to resolve the two bodies and support the spacecraft autonomous navigation to the target, and to locate the impact site precisely and characterize its local surface features. To complement such observations, the Light Italian Cubesat for Imaging of Asteroids (LICIACube, [7]) will be released from DART ten days before the impact, and autonomously guided through a flyby with closest approach distance of ~55 km from the target. LICIACube cameras LEIA (LICIACube Explorer Imaging for Asteroid - narrow angle camera) and LUKE (LICIACube Unit Key Explorer – wide angle camera) will then safely witness the redirection test in-situ, while its crater, as well as the ejecta and plume are being formed.Boulders SFD on Didymos systemBoulders/large blocks on asteroids are mainly interpreted as produced by target fragmentation and excavation due to high-velocity impact processes. They are the largest fragments excavated during an impact and are typically found within the crater or in its proximity, because they have not reached the escape velocity [8]. Instead, on rubble-pile asteroids boulders (typically the largest ones) are products of the reaccumulation process that formed the minor body itself, and may not be correlated to the observed craters [9]. For both cases, these blocks provide information on impact cratering processes occurring on low gravity bodies or on their parent body disruption event: their size-frequency distribution (SFD) fitting indices are therefore pivotal to provide hints on the fragment/boulder formation and/or degradation processes.Deriving boulder SFD and the corresponding power/exponential-law indices has been an important scientific topic addressed in several fly-by and orbital missions to minor bodies [e.g. 10-12]: it will be accomplished on the Didymos system as well.Four minutes before the impact the last image that contains all of Didymos will be taken by DRACO, with an expected spatial scale of 7 m/pixel. 120 seconds before impact, the last DRACO image containing any part of Dydimos will be taken, with a maximum resolution of 3.5 m [13]. DRACO will image all of Dimorphos ~50 cm/pixel ~17 seconds before impact and plans to return at least one higher-resolution image before impact. These final image(s) will have pixel scales

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

The classical distinction between asteroids (rocky and inert), and comets (ice-rich and active) has been blended in the last 15 years, leading to a more nuanced picture. Both classes are now believed to be simply end-members of a physical and dynamical continuum. The study of TRANSient NEOs (Near-Earth Objects showing characteristics of both classes) could be the missing link to understanding this new paradigm of small bodies continuum. We decided to investigate the TRANSNEO population because i) their repeated passages around the Sun make it in principle easier to detect a potential activity; ii) they can be extremely accessible for observations and a future space mission; iii) activity on NEO surfaces has been recently discovered even on apparently inactive places, thus attracting the interest of various space agencies. One of these intriguing bodies (3200 Phaethon) will indeed be the target of the JAXA DESTINY+ space mission, scheduled to be launched in 2025. In 2022, we started a new project called “TRANSNEO” financed by the Italian National Institute for Astrophysics (INAF) to characterize via spectroscopy, photometry, and polarimetry these bodies that often both show the asteroid/comet designation. We will present the latest results of the TRANSNEO project and put it in the larger context of active bodies in the Solar System. Acknowledgments: This research was funded by the Italian National Astrophysical Institute (INAF) - Call for Fundamental Research 2022. E.D. acknowledges the support from the ASI (ASI-INAF agreement AC n. 2022-1-HH.0).

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.

NASA's Double Asteroid Redirection Test (DART) mission was the first to demonstrate asteroid deflection, and the mission's Level 1 requirements guided its planetary defense investigations. Here, we summarize DART's achievement of those requirements. On 2022 September 26, the DART spacecraft impacted Dimorphos, the secondary member of the Didymos near-Earth asteroid binary system, demonstrating an autonomously navigated kinetic impact into an asteroid with limited prior knowledge for planetary defense. Months of subsequent Earth-based observations showed that the binary orbital period was changed by –33.24 minutes, with two independent analysis methods each reporting a 1 σ uncertainty of 1.4 s. Dynamical models determined that the momentum enhancement factor, β , resulting from DART's kinetic impact test is between 2.4 and 4.9, depending on the mass of Dimorphos, which remains the largest source of uncertainty. Over five dozen telescopes across the globe and in space, along with the Light Italian CubeSat for Imaging of Asteroids, have contributed to DART's investigations. These combined investigations have addressed topics related to the ejecta, dynamics, impact event, and properties of both asteroids in the binary system. A year following DART's successful impact into Dimorphos, the mission has achieved its planetary defense requirements, although work to further understand DART's kinetic impact test and the Didymos system will continue. In particular, ESA's Hera mission is planned to perform extensive measurements in 2027 during its rendezvous with the Didymos–Dimorphos system, building on DART to advance our knowledge and continue the ongoing international collaboration for planetary defense.

AbstractAsteroids smaller than 10 km are thought to be rubble piles formed from the reaccumulation of fragments produced in the catastrophic disruption of parent bodies. Ground-based observations reveal that some of these asteroids are today binary systems, in which a smaller secondary orbits a larger primary asteroid. However, how these asteroids became binary systems remains unclear. Here, we report the analysis of boulders on the surface of the stony asteroid (65803) Didymos and its moonlet, Dimorphos, from data collected by the NASA DART mission. The size-frequency distribution of boulders larger than 5 m on Dimorphos and larger than 22.8 m on Didymos confirms that both asteroids are piles of fragments produced in the catastrophic disruption of their progenitors. Dimorphos boulders smaller than 5 m have size best-fit by a Weibull distribution, which we attribute to a multi-phase fragmentation process either occurring during coalescence or during surface evolution. The density per km2 of Dimorphos boulders ≥1 m is 2.3x with respect to the one obtained for (101955) Bennu, while it is 3.0x with respect to (162173) Ryugu. Such values increase once Dimorphos boulders ≥5 m are compared with Bennu (3.5x), Ryugu (3.9x) and (25143) Itokawa (5.1x). This is of interest in the context of asteroid studies because it means that contrarily to the single bodies visited so far, binary systems might be affected by subsequential fragmentation processes that largely increase their block density per km2. Direct comparison between the surface distribution and shapes of the boulders on Didymos and Dimorphos suggest that the latter inherited its material from the former. This finding supports the hypothesis that some asteroid binary systems form through the spin up and mass shedding of a fraction of the primary asteroid.

Images collected by the DART and LICIAcube spacecraft provide the first resolved views of the Didymos binary asteroid system. These images reveal that the primary asteroid, Didymos, is flattened and has a non-circular equatorial perimeter. At high elevations, its surface is undulating and contains large boulders and craters; at low elevations its surface is smoother and possesses fewer large boulders and craters. Didymos' moon, Dimorphos, possesses a uniform surface covered by boulders, several asteroid-wide lineaments, and a handful of craters. The surfaces of both asteroids include boulders that are large relative to their host body, suggesting that both asteroids are rubble piles. Models run to explain the observations indicate that Didymos has a surface cohesion ≤1 Pa and an interior cohesion of ~$10 Pa, while Dimorphos has a surface cohesion of <0.9 Pa. Crater size-frequency analyses indicate the surface age of Didymos is 40-130x older than Dimorphos, with likely absolute ages of ~12.5 Myr and <0.3 Myr, respectively. Solar radiation could have increased Didymos' spin rate leading to internal deformation and surface mass shedding, which likely created Dimorphos. If part of the Bauptistina family, Didymos likely represents the latest of multiple asteroid generations stemming from the original parent.