Pedro Henrique Hasselmann

On 2022 September 26, the NASA/DART spacecraft performed the first-ever test of the kinetic impactor technique by hitting Dimorphos, the moon of the asteroid (65803) Didymos. The Italian Space Agency (ASI)/Light Italian CubeSat for Imaging of Asteroids (LICIACube) witnessed the event in situ. In this work, we used images from both Didymos Reconnaissance and Asteroid Camera for Opnav (DRACO) and LICIACube Explorer Imaging for Asteroid (LEIA) instruments on board the two spacecraft to search for small objects that may be present around the primary before the impact, to provide hints on the complete dynamical characterization of the system. This will be compared to the future environment the European Space Agency (ESA)/Hera mission will encounter in late 2026. We found no unknown objects larger than ∼50 m in the entire Hill sphere. When considering closer regions with respect to the primary object, the limiting size gets smaller, reaching a minimum diameter equal to ∼2 m within a radial distance of ∼2 km from Didymos. Despite the dynamical environment in the system being extremely perturbed and unstable, there is still a small chance that large objects could find a stable niche in the phase space of the Didymos–Dimorphos system, but the null result of our work is a strong indication that this niche is either nonexistent or empty.

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.

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 μm 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 . ° 6 to 110 . ° 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 × 10⁷ kg. Results indicate that the PSD of ejecta in the nascent plume follows a single power-law coefficient (k ≈ −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 ≈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 ∼50 Pa).

Introduction: Near-Earth Objects (NEOs) provide a window into the smallest population of asteroids and comets that originated from more distant regions of the Solar System. Most of them are product of collisional processes at various stages of the Solar System's evolution, thus important for probing compositions that may have contributed to the delivery of water and organics to Earth and the inner planets.As NEO discoveries increase—currently at about 3,000 objects per year—the majority are not followed up with physical characterization. These properties would offer insights into their internal structure and material strength in the event of atmospheric entry [1,2], not to mention their potential as targets for future mining, exploration, and planetary defense missions [3]. Therefore, anticipating a rise in new discoveries following the start of LSST operations, we initiated a year-long, monthly photometric observation campaign of NEOs discovered in the past two years (2022–2023) and visible with the VLT Survey Telescope (VST) at Cerro Paranal. The main instrument on the VST is OmegaCAM, a multi-filter, 32-CCD camera with a Field of View (FoV) of 1 square degree [4]. This capability enables the tracking of very fast-moving NEOs and also brings important collateral science: many other small bodies can be observed simultaneously. These secondary targets are identified and analyzed to enhance their characterization and astrometric positions.Observations: The observations were carried between February to September 2023, two monthly nights. The targets were observed cycling through SDSS r’i’z’g’r’ filters in exposure times of 10 to 30s depending on the observational conditions. Every target was observed for 1 hour. In total, we acquired 5519 image cubes covering 72 NEAs, and possibly 5 to 10 times this number in SSO in the background depending on the pointing region. The magnitude limit is estimated to r’=21.5 for SNR=3 and exposure time of 20s. The cubes are radiometrically calibrated in the Astro-Wise environment through the VST pipeline available by INAF-OAC [5]. The final products are single Mosaics in absolute Jansky flux and astrometrics. We are also provided with a list of sources measured with SExtractor. See Fig. 1 for an example of final product, where the main target and secondary targets are visible.Methodology: The analysis is carried through procedures developed in Python3 language and the use of Scikit-image, Astropy, Photutils, and Astroquery libraries, and ordered in three steps:1. Querying SSOs and Fixed Sources in the Field. We catalog all fixed and moving sources over mag=23 for identification of the main and secondary targets, and obtaining the photometry of field stars for flux quality check. We also operate a check on the celestial coordinate and correct any miss-offsets present. The moving object ephemeris is obtained from OBSPM/IMCEE service and the fixed sources from several catalogs bundled under the Astropy/VO service.2. Target Tracking, Cube alignment, stacking. We crop all loci of 0.04°x0.04° from the field that might show potential SSOs, and then align it according to Sky-Fixed and SSO-fixed coordinates. Then fixed sources are removed, we applied Hough Transform [7] to detect linear tracks related to SSO apparent motion. Then, the cube is centered onto the target, and then a stacked cube product is provided as well.3. Aperture, Lorenz and PSF Photometry. Photometry for the target and field stars are provided through aperture, Lorenz fitting, and 2D PSF photometry analysis. We also check for signs of fast rotation throughout the image sequences. We then compare the field star photometry with SDSS and VST/Atlas sources to cross-check the flux quality [8,9].Preliminary Results and Future Steps: To date, data reduction has been completed for the first 4 observing months and for all 30 primary targets and secondary objects under exposure time ≥ 20s (the example of a section of a light-curve in Fig. 2). The color analysis is concluded for the March 2023 run, the results (Fig. 3) show that awhile the asteroids cluster around the feature and featureless loci, we have samples of redder and bluer asteroids, generally associated to organic or carbon-rich bulk compositions.In September 2024, new NEOVST observations have been scheduled between February 2025 and September 2025. We are now focusing on scattered monthly observations of newly discovered NEOs, with exposure times of 30s (r’) to 50s (z’), and two sequences of 1 hrs each target. We now aim to improve the signal of the background stars for better astrometric positioning, and better sampling for the phase and rotational curves by compiling data from two separated nights. (a) (b)Fig.1: (a) Full mosaic of 32 CCDs for the acquisition of 2023-02-04 UT 05:15:09 in SDSS r’ for the main target NEA 2022 YM5. (b) The main target (magenta) and secondary targets (yellow) in the FOV. Fig.2: A sequence of AB magnitudes obtained for the asteroid 2001 EV2 for the run of March 2023. The error bars are within the symbol size.Fig.3: SDSS color mosaic of the asteroids observed in the March 2023 run (7NEAs+15MBAs). The data is overlay by the approx. loci of “S-like” and “C-like” asteroids. Many objects lack the SDSS z’ magnitude due to the weaker band efficiency.References: [1]Perna,D.,Barucci,M.A.,&Fulchignoni,M. 2013, A&ARv,21,65. [2]Perna,D.,Dotto,E.,Ieva,S., et al. 2016, AJ 151,11. [3]Sanchez,J.-P., & McInnes,C.R. 2013, ed. V.Badescu, 439 [4]K.Konrad,R.Bender,E.Cappellaro, et al. 2004, GIA 5492, 484–494. [5]McFarland,J.P.,Verdoes-Kleijn,G., Sikkema,G. et al. 2013, ExpAstron 35, 45–78. [6]Bertin,E.&Arnouts,S. 1996, A&ASupp 317, 393. [7]P.V.C.Hough. 1959, Proc.Int.Conf. High Energy Accelerators and Instrumentation. [8] Gunn,J. E.; Siegmund,W.A.; Mannery,E.J., et al. 2006, ApJ 131,2332–2359....

On 2022 September 26 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 Light Italian Cubesat for Imaging of Asteroids (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 of up to 52 m s⁻¹. 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.

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 μm) 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.

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

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.

The ASI cubesat LICIACube has been part of the first planetary defense mission DART, having among its scopes to complement the DRACO images to better constrain the Dimorphos shape. LICIACube had two different cameras, LEIA and LUKE, and to accomplish its goal, it exploited the unique possibility of acquiring images of the Dimorphos hemisphere not seen by DART from a vantage point of view, in both time and space. This work is indeed aimed at constraining the tridimensional shape of Dimorphos, starting from both LUKE images of the nonimpacted hemisphere of Dimorphos and the results obtained by DART looking at the impacted hemisphere. To this aim, we developed a semiautomatic Computer Vision algorithm, named VADER, able to identify objects of interest on the basis of physical characteristics, subsequently used as input to retrieve the shape of the ellipse projected in the LUKE images analyzed. Thanks to this shape, we then extracted information about the Dimorphos ellipsoid by applying a series of quantitative geometric considerations. Although the solution space coming from this analysis includes the triaxial ellipsoid found by using DART images, we cannot discard the possibility that Dimorphos has a more elongated shape, more similar to what is expected from previous theories and observations. The result of our work seems therefore to emphasize the unique value of the LICIACube mission and its images, making even clearer the need of having different points of view to accurately define the shape of an asteroid.

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.