Adriano Campo Bagatin

Context . Wide-field astronomical surveys have significantly expanded the population of known trans-Neptunian objects. However, detecting very distant bodies remains challenging due to their extremely slow apparent motion and faint magnitudes. Multi-epoch transient surveys provide an opportunity to identify such objects by exploiting the positional consistency in observations obtained on different nights. Aims . We developed and validated an automated detection pipeline to search archival multi-epoch survey data for faint, slow-moving bodies in the outer Solar System, and we assessed its potential for discovering previously unknown distant objects. Methods . We applied our pipeline to observations from the Catalina Sky Survey (CSS), analysing repeated images of the same sky regions obtained over multiple nights. The algorithm identifies candidate objects based on positional consistency and motion across epochs. Its performance was evaluated through recovery tests using catalogued objects and synthetic sources injected into the images, allowing us to quantify the detection efficiency as a function of apparent magnitude. Results . The pipeline successfully recovered the distant trans-Neptunian objects Sedna and Eris in blind tests where prior catalogue information was disabled. The recovery fraction of catalogued objects approaches 100% for objects brighter than 19.5 mag in the V band, while the synthetic-source recovery efficiency is approximately 90% for objects brighter than 20.5 mag in the Gaia G band and decreases to approximately 54% in the G = 21.0–21.5 magnitude bin under the observational conditions of the CSS. The analysis also resulted in the serendipitous detection of Sycorax, an irregular satellite of Uranus. In addition, two previously unknown distant Solar System objects, 2020 TZ114 and 2022 BO71, were identified and later designated by the Minor Planet Center. Conclusions . The results demonstrate that multi-epoch motion-based detection strategies applied to archival survey data provide an effective approach for identifying faint and distant Solar System bodies. Similar methods applied to current and future wide-field surveys, such as the Vera C. Rubin Observatory Legacy Survey of Space and Time, have substantial potential to expand the census of the outer Solar System.

We present a 3D reconstruction of the ejecta plume generated by the DART impact on Dimorphos based on LUKE images acquired by LICIACube. Using adaptive histogram equalization and geometric coregistration from multiple vantage points, we identified and tracked extended ejecta features and reconstructed their 3D spatial distribution with a voxel-based method. The reconstructed ejecta field shows strong anisotropy. An azimuth-matched comparison with the published elliptical cone highlights coherent, direction-dependent departures from a simple conic surface, despite broad agreement on the global cone orientation. This quantifies nonaxisymmetric structures that cone models cannot capture. We derived lower limits to ejecta velocities ranging from 20 to 50 m s ⁻¹ , consistent with numerical simulations of hypervelocity impacts into weak, porous targets. Compared to laboratory experiments, these values correspond to few-meter launch depths, suggesting a significant role of near-surface boulders in the ejecta distribution. Complementing this ejecta filament analysis, we studied 105 isolated comoving diffuse ejecta features, tracked up to 7 km from the impact site. These features followed highly tangential (85 ^∘ –92 ^∘ from the impact direction) trajectories relative to Dimorphos’s surface. Their velocity distribution peaks around 50 m s ⁻¹ , indicating that crater excavation persisted throughout the imaging sequence. Our results challenge and refine previous cone-based ejecta distribution models, offering new insights into the complex nature of impact-induced ejecta and improving constraints relevant for planetary defense strategies. Given these new insights, we urge the designers of future planetary defense missions to take into consideration anisotropic ejecta models for more realistic estimates of the imparted momentum via a kinetic impactor technique.

Understanding how the observed size distribution of Kuiper Belt objects emerged from the primordial planetesimal population remains a major challenge in planetary science. In particular, the similarity between the size distributions of dynamically hot and cold populations in the 100 − 400 km range calls for a unified explanation. Motivated by this observational constraint and by theoretical models of pebble accretion, we model the coupled dynamical and collisional evolution of the trans-planetary disc under the early instability scenario. Here we show that a common planetesimal formation mechanism operating up to about 400 km and modulated by an exponential taper shape, combined with a transition to a shallow power law distribution in the inner disc, can reproduce the current size-frequency distributions of cold and hot populations. This outcome requires assuming that planetesimals were weaker to impacts than previously thought. Our results connect formation models with current observations, thereby constraining the early conditions of the Solar System and the properties of planetesimals.

In this paper, the shapes of asteroids and the stability on their surfaces are characterized using super-ellipsoids, i.e. geometric shapes defined from the tri-axial ellipsoid equation replacing the exponent 2 by any positive exponent. The concept of dynamically equivalent equal-mass super-ellipsoid (DEEMSE) of a body is introduced as a homogeneous super-ellipsoid with equal principal moments of inertia and mass as the body. The overall shapes of high-resolution polyhedral shape models of Bennu, Ryugu, Vesta, Ceres and Eros are suitably described by their DEEMSE adjusting the exponent to best fit their surface. Next, for a spinning super-ellipsoid with a test-mass m on its surface, the minimum spin period to avoid detachment is computed along with the corresponding slope angle, which is the minimum friction angle to avoid sliding of m . The surface stability of different super-ellipsoidal bodies is analysed considering that the smaller the slope angle is, the less friction is required to avoid sliding, so the more stable the surface is. For fast rotation relative to the limit detachment rate, top-shaped bodies have more stable surfaces than ellipsoidal ones. For slower rotation, ellipsoids have more stable surfaces, even with zero slope angle (unconditional stability) under given conditions that nearly hold for Ceres and Vesta equivalent ellipsoids at their current spin rates. Those outcomes are compatible with rubble-pile outer asteroid structures reshaping to minimize surface tensions depending on the spin rate. Finally, the surface stability of Didymos is discussed as related to its bulk density and shape.

Understanding the physical characteristics of small Solar System bodies is important not only for refining formation and evolution models but also for space mission operations. Although several kilometre-sized asteroids have been visited by spacecraft, asteroid 1998 KY₂₆-the final target of Hayabusa2#, the extended mission of the Japan Aerospace Exploration Agency's Hayabusa2 spacecraft-will be the first decametre-scale asteroid to be explored in situ. Its small size and rapid spin place it above the upper limit on the rotation rate, indicating it may differ from previously studied bodies. In this work, we conducted a photometric campaign during 1998 KY₂₆'s close approach to Earth in 2024, revealing a high optical albedo and Xe-type colours. We determine its spin period to be (5.3516 ± 0.0001) minutes-half the period of earlier estimates. Lightcurve inversion produces retrograde pole solutions in both convex and non-convex shape models. Combined with 1998 Goldstone radar data, these results give a diameter of (11 ± 2) m, three times smaller than previously derived values. The derived cohesive strength levels necessary to keep the structure intact, which is less than 20 Pa, suggest a possibility of the asteroid's rubble pile structure, though this finding does not rule out its monolithic structure. These results can be validated with future James Webb Space Telescope observations. Our comprehensive characterisation can inform the planning of the Hayabusa2# rendezvous in 2031 and helps pave the way for future studies of dark comets.

The successful impact of the Double Asteroid Redirection Test (DART) spacecraft on Dimorphos enabled the first-ever extensive observation of a postimpact ejecta tail from a binary asteroid system. Studying the ejecta can provide insights into impact physics and asteroid composition and inform future asteroid missions. In this research, the orbital capture of the impact ejecta around the Didymos binary asteroid system is investigated. The ejecta dynamics are described using an augmented bicircular restricted four-body model, which incorporates the binary’s irregular gravity field and solar radiation pressure (SRP) acceleration. Typical periodic orbit (PO) families, including planar Lyapunov and terminator orbits, are selected as the candidates for capture analysis. The candidate POs are perturbed and backward-propagated using the invariant manifold theory, and eligible trajectories intersecting the asteroids’ surfaces are recorded. The ejecta characteristics of different POs are summarized from three principal aspects: ejection location, ejection velocity, and ejection angle. The influence of two critical factors is qualitatively assessed, including the geometry of the asteroids in the binary system and the strength of SRP acceleration. Lastly, the likelihood for the ejecta from the DART impact being transferred to candidate POs is assessed.

Hypervelocity impacts play a significant role in the evolution of asteroids, causing material to be ejected and partially reaccreted. However, the dynamics and evolution of ejected material in a binary asteroid system have never been observed directly. Observations of Double Asteroid Redirection Test (DART) impact on asteroid Dimorphos have revealed features on a scale of thousands of kilometers, including curved ejecta streams and a tail bifurcation originating from the Didymos system. Here we show that these features result naturally from the dynamical interaction of the ejecta with the binary system and solar radiation pressure. These mechanisms may be used to constrain the orbit of a secondary body, or to investigate the binary nature of an asteroid. Also, they may reveal breakup or fission events in active asteroids, and help determine the asteroid’s properties following an impact event. In the case of DART, our findings suggest that Dimorphos is a very weak, rubble-pile asteroid, with an ejecta mass estimated to be in the range of (1.1-5.5)×10⁷kg.

Understanding the physical characteristics of small bodies in the Solar System is crucial for refining models of their formation and evolution. Although several kilometre-sized asteroids have already been visited by spacecraft, 1998 KY26 will be the first asteroid in the decametre range to be explored in situ. Its diameter and spin period place it above the spin barrier, suggesting that its formation and properties may differ from those of previously visited bodies. However, the key physical characteristics of 1998 KY26 remain poorly understood. We conducted a photometric observing campaign during 1998 KY26’s close approach to Earth in 2024. Our observations revealed that 1998 KY26 has a high optical albedo and colours consistent with an E-type taxonomy. We also determined its spin period to be (5.3516 ± 0.0001) minutes—twice as fast as previously reported. Using lightcurve inversion methods, we derived a retrograde pole solution and constructed convex and non-convex shape models. By integrating these models with Goldstone radar data from 1998, we estimated 1998 KY26’s diameter to be (11 ± 2) m. The most likely structure for 1998 KY26 is monolithic, yet a fine grained rubble-pile structure is theoretically possible given its required small strength level. We found that it will be possible to validate these results with future JWST observations. Our comprehensive characterisation of 1998 KY26 can inform the planning of the Hayabusa2# spacecraft’s rendezvous encounter, scheduled for July 2031. Additionally, it provides valuable insights into the non-gravitational forces acting on small Solar System bodies, enhancing our understanding of their orbital evolution which could shed light on the nature of dark comets.