arXiv subjects

Marco Delbo

Publications and source records attributed to Marco Delbo.

At least 19 recordsLinked to original sources

arXiv2026

Twin Impact Lunar Telescope network: Lunar Impact Flash observations of the 2025 Geminids

Meteoroid impacts on the Moon, observed from Earth as flashes typically lasting a few tens of milliseconds, have been monitored for three decades for determining meteoroids' size and mass frequency distribution in the cm to dm range. Studies link these observed impact events to fresh craters advancing our understanding of energy partitioning during an impact. Currently we are transitioning to a new era where lunar impact flashes (LIFs) can be used to supplement upcoming lunar seismology to study the internal lunar structure. Here we present results from the first station of a telescope network under development for continuous LIF monitoring. Observations were carried out during the Geminids 2025 campaign, initiated by the LUMIO Science Team in the framework of their public engagement activities. We detected 53 potential impact flashes and confirmed 11 of them through multiframe observations, and independent detections by other observers. We present evidence suggesting that some of the yet unconfirmed events may be real. Our confirmed events range between magnitude +7.5 and +10.4, primarily in the V and R band. We obtained a high rate of observations per hour, highlighting the importance of high ZHR meteoroid streams for observing LIFs. We also discuss the scientific value of potential LIFs that remain unconfirmed in optical data alone. Even without multi station confirmation, these events can correlate to seismic signals in future lunar seismic networks, thereby providing useful physical constraints on impact processes. This approach would also allow stations equipped with a single telescope/camera to meaningfully contribute to the network.

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arXiv2026

Dark asteroids exhibiting intermediate characteristics between C and X types

Large main-belt asteroids with visible geometric albedos below 0.1 are predominantly classified within the C- and X-complex spectroscopic classes. C-type and dark X-type asteroids typically exhibit flat to slightly negative and positive spectral slopes, respectively. They are further distinguished by the presence (for C-types) or absence (for dark X-types) of a shallow absorption feature near 1.0-1.3 micron. We serendipitously discovered that the asteroids 1093 Freda and 1390 Abastumani display spectral characteristics intermediate between these two classes, combining a positive visible-to-near-infrared spectral slope with a shallow absorption band. A search in the literature reveals additional asteroids with similar properties. The existence of such objects, spanning a continuum of spectral shapes between C- and dark X-types, may point to a common genetic origin. Their spectral behavior could be explained by the presence of cronstedtite, an Fe-rich serpentine, on their surfaces.

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arXiv2026

Shape and spin axis determination of the Tianwen-2 target asteroid (469219) Kamo'oalewa from lightcurve inversion

Near-Earth asteroid (469219) Kamo'oalewa is an Earth quasi-satellite, temporarily trapped in a 1:1 orbital resonance with our planet. Despite its dynamical relevance and the hypothesis that it may be a lunar ejecta fragment, its physical properties are still poorly constrained. In particular, no reliable models of its shape and spin state have been published so far. The scientific interest in this object is further enhanced by its selection as the primary target of the Chinese Tianwen-2 mission, which aims to rendezvous with this asteroid and return samples of it to Earth. The aim of this work is to determine the shape and spin axis orientation of Kamo'oalewa by means of photometric telescope observations and lightcurve inversion. We analyzed lightcurves obtained during several apparitions using the well-established algorithm, based on convex shape modeling. We derived a convex shape model and estimated the spin pole orientation. In the preferred solution, the pole is located at ecliptic coordinates {\lambda}, {\beta} = (126,-16) degrees, with a sidereal rotation period of P~0.465 h. Conclusions. Our results provide the first direct constraints on the rotational state and morphology of Kamo'oalewa, information of key importance in preparation for the upcoming Tianwen-2 sample-return mission.

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arXiv2026

Gaia DR3 supervised classification of asteroid reflectance spectra

We present a supervised, probabilistic taxonomic classification of asteroid reflectance spectra from Gaia Data Release 3 (DR3). Using high-quality Gaia DR3 spectra and a reference set of spectra from the literature consisting exclusively of asteroids with robust spectroscopic taxonomic types, we construct a principal-component (PC) representation of the Gaia reflectances. For each major spectral complex (C, S, X) and several end-member classes (B, D, A, L, K, V), we model the distribution of reference objects in PC space using multivariate kernel density estimation (KDE). This yields likelihoods for each spectral class and provides a quantitative measure of classification confidence. Validation against a sample of objects with known spectral classes demonstrates good performance for classes with distinctive reflectance signatures, including the S-complex, D, V, and A types. Spectrally continuous classes (B-C-complex, K-L-S-complex, and X-complex) show the expected degrees of mixing given the limited wavelength range of Gaia's spectrophotometry. We further explore the compositional structure of six major asteroid collisional families using our Gaia-derived spectral classes, finding excellent agreement with ground-based spectroscopy and revealing enhanced detections of olivine-rich A type material in the Flora and Eunomia families, as well as new insights into the spectral diversity of the Tirela family. The resulting catalogue constitutes a fully probabilistic taxonomic classification for the full Gaia DR3 asteroid sample. It offers a resource for studying the compositional structure of the main belt, identifying family interlopers, and linking asteroid populations to meteorite groups, and establishes a methodological framework for future Gaia releases, in particular for the validation of the Gaia DR4, expected by the end of 2026.

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arXiv2025

Searching for primitive, dark, spectrally red asteroid families in the main belt with Gaia

Dark asteroids with featureless neutral to red spectra are of particular interest due to their ability to potentially harbour primitive, hydrated, and possibly organic-rich material. These asteroids belong to the spectroscopic C-complex, to the X-types with low geometric visible albedo values as well as to the T- and D-type end members of the Bus-DeMeo spectroscopic taxonomy. Here we used Gaia Data Release 3 visible reflectance spectra to study the average spectral profiles of the C- and X-complex asteroid families in the central and outer main belt (orbital semi-major axis between 2.5 - 3.7~au). We found that eight of these families, namely 96 Aegle, 627 Charis, 1484 Postrema and 5438 Lorre, previously classified as C-complex families, and 322 Phaeo, 1303 Luthera, 5567 Durisen and 53546 2000BY6 previously classified as X-complex families, have redder slopes than implied by their previous classification and could be better classified as T-/D-type families. Some of these families may also feed the near-Earth asteroid population, being responsible for the observed T-/D-type excess. However, the analysis of their principal components of Gaia Data Release 3 spectra suggest that further near-infrared observations are needed in order to verify this identification.

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arXiv2025

Gaia and IRTF abundance of A-type main belt asteroids

The Missing Mantle Problem refers to the apparent scarcity of olivine rich (A-type) asteroids in the main belt, despite expectations that such bodies should be common if differentiated parent bodies were widely disrupted. Conversely, A-types appear relatively more abundant among near-Earth asteroids. We present a revised estimate of the A-type abundance in the main belt by combining Gaia Data Release 3 (DR3) reflectance spectra with near-infrared observations from NASA IRTF. We applied principal component analysis (PCA) to Gaia DR3 visible spectra to identify A-type candidates and confirmed a subset through IRTF spectroscopy. Using these data and literature results, we derived the A-type probability distribution as a function of DR3 principal components, and from this, estimated their abundance across heliocentric distances and collisional families. We find that A-types constitute (2.00 +/- 0.15)% of main-belt asteroids significantly higher than previous estimates. Some families, such as Vesta and Flora, show enhanced A-type fractions, while others (e.g. Themis, Hygiea) contain few or none. The elevated abundance in the Flora family supports the existence of an additional differentiated parent body in the inner belt, besides Vesta. These findings indicate that olivine-rich material is more widespread than previously thought, offering new constraints on the Missing Mantle Problem and on early Solar System differentiation processes.

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arXiv2025

Physical Characterization of Asteroid (16583) Oersted Combining Stellar Occultation and Photometric Data

We report a successful observation of a stellar occultation by asteroid (16583) Oersted, enabling a detailed physical characterization of its shape, spin state, and surface properties. Our goal is to determine the physical parameters of Oersted by combining multi-chord occultation timing, sparse optical photometry, and thermal infrared observations. Such asteroids (size$\sim$20 km) are rarely modeled in this detail due to observational limitations, making Oersted a valuable case study. We applied convex lightcurve inversion to sparse photometric data to derive an initial shape and spin state. This model was then refined and scaled using non-convex shape modeling with the ADAM algorithm, incorporating constraints from the occultation chord profile. Thermophysical modeling based on WISE thermal infrared fluxes was used to determine the asteroid's effective diameter, geometric albedo, and thermal inertia. The non-convex shape model reveals localized surface concavities and provides a size estimate consistent with radiometric measurements. The derived thermal inertia is typical for asteroids of comparable size. This work demonstrates the effectiveness of combining stellar occultations, photometry, and thermal infrared data for asteroid modeling and highlights the valuable contributions of citizen scientists, who played a key role in capturing the occultation and constraining the asteroid's profile.

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arXiv2025

An ancient L- type family associated to (460) Scania in the Middle Main Belt as revealed by Gaia DR3 spectra

Asteroid families are typically identified using hierarchical clustering methods (HCM) in the proper element phase space. However, these methods struggle with overlapping families, interlopers, and the detection of older structures. Spectroscopic data can help overcome these limitations. The Gaia Data Release 3 (DR3) contains reflectance spectra at visible wavelengths for 60,518 asteroids over the range between 374-1034 nm, representing a large sample that is well suited to studies of asteroid families. Using Gaia spectroscopic data, we investigate a region in the central Main Belt centered around 2.72 AU, known for its connection to L- type asteroids. Conflicting family memberships reported by different HCM implementations underscore the need for an independent dynamical analysis of this region. We determine family memberships by applying a color taxonomy derived from Gaia data and by assessing the spectral similarity between candidate members and the template spectrum of each family. We identify an L- type asteroid family in the central Main Belt, with (460) Scania as its largest member. Analysis of the family's V-shape indicates that it is relatively old, with an estimated age of approximately 1 Gyr, which likely explains its non detection by the HCM. The family's existence is supported by statistical validation, and its distribution in proper element space is well reproduced by numerical simulations. Independent evidence from taxonomy, polarimetry, and spin-axis obliquities consistently supports the existence of this L- type family. This work highlights the value of combining dynamical and physical data to characterize asteroid families and raises questions about the origin of L- type families, potentially linked to primordial objects retaining early protoplanetary disk properties. Further spectroscopic data are needed to clarify these families.

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arXiv2025

Multi-epoch spectro-photometric characterization of the minimoon 2024 PT$_5$ in the visible and near-infrared

2024 PT$_5$ is a tiny ($D\leq10$ m) near-Earth asteroid (NEA) discovered in August 2024. 2024 PT$_5$ was gravitationally bound to the Earth-Moon system from September to November 2024 and classified as a minimoon. Several quick response observations suggest the lunar ejecta origin of 2024 PT$_5$, while rotation state and albedo, essential properties to investigate its origin, are not well constrained. We performed visible to near-infrared multicolor photometry of 2024 PT$_5$ from data taken using the TriColor CMOS Camera and Spectrograph (TriCCS) on the Seimei 3.8 m telescope during 2025 January 4-10. The Seimei/TriCCS observations of 2024 PT$_5$ cover phase angles from 14 deg to 27 deg, and were obtained in the $g$, $r$, $i$, and $z$ bands in the Pan-STARRS system. In addition, we analyzed $Y$, $J$, $H$, and $K$ photometry taken with the Multi-Object Spectrograph for Infrared Exploration (MOSFIRE) on the Keck I 10-m telescope taken on 2025 January 16-17. Our lightcurves show brightness variations over time periods of several tens of minutes. We infer that 2024 PT$_5$ is in a tumbling state and has a lightcurve amplitude of about 0.3 mag. Visible and near-infrared color indices of 2024 PT$_5$, $g-r=0.567\pm0.044$, $r-i=0.155\pm0.009$, $r-z=0.147\pm0.066$, $Y-J=0.557\pm0.046$, $J-H=0.672\pm0.078$, and $H-Ks=0.148\pm0.098$, indicate that 2024 PT$_5$ is an S-complex asteroid, largely consistent with previous observations. Using the $H$-$G$ model, we derived an absolute magnitude $H_{V,HG}$ of $27.72\pm0.09$ and a slope parameter $G_V$ of $0.223\pm0.073$ in V-band. A geometric albedo of 2024 PT$_5$ is derived to be $0.26\pm0.07$ from the slope of its photometric phase curve. This albedo value is typical of the S- and Q-type NEAs. The color properties of 2024 PT$_5$ derived from our observations match rock samples taken from the lunar surface, which agrees with previous studies.

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arXiv2025

Size Constraint on Hayabusa2 Extended Mission Rendezvous Target 1998~KY$_{26}$ via VLT/VISIR Non-detection

1998~KY$_{26}$ is a tiny near-Earth asteroid ($H=26.1$) discovered in 1998. It has been selected as the target of the Hayabusa2 extended mission, which will rendezvous with 1998 KY$_{26}$ in 2031. However, one of the most basic physical properties, size, remains poorly constrained, posing potential challenges for spacecraft operations. We aimed at constraining the size of 1998 KY$_{26}$ by means of thermal infrared observations. We performed thermal infrared observations of 1998 KY$_{26}$ using the ESO Very Large Telescope/VISIR on three consecutive nights in May 2024. After stacking all frames, we find no apparent detection of 1998 KY$_{26}$ on the resulting images. The upper-limit flux density of 1998 KY$_{26}$ is derived as 2 mJy at 10.64 $\mu$m. From this upper-limit flux density obtained via non-detection, we conclude that the diameter of 1998 KY$_{26}$ is smaller than 17 m with thermophysical modeling. This upper limit size is smaller than the radar-derived 30 ($\pm$ 10)\,m. Our size constraint on 1998 KY$_{26}$ is essential for the operation of the Hayabusa2 spacecraft during proximity operations using remote sensing instruments as well as a possible impact experiment using the remaining projectile.

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arXiv2025

The discovery and characterization of Earth-crossing asteroid 2024 YR$_4$

We describe observations and physical characteristics of Earth-crossing asteroid 2024 YR$_4$, discovered on 2024 December 27 by the Asteroid Terrestrial-impact Last Alert System. The asteroid has semi-major axis, $a$ = 2.52 au, eccentricity, $e$ = 0.66, inclination $i$ = 3.41$^{\circ}$, and a $\sim$0.003 au Earth minimum orbit intersection distance. We obtained g, r, i, and Z imaging with the Gemini South/Gemini Multi-Object Spectrograph on 2025 February 7 and Y and J imaging with the Keck/Multi-Object Spectrometer For Infra-Red Exploration on 2025 February 12. We measured a g-i spectral slope of 13$\pm$3 $\%$/100 nm, and color indices g-r = 0.70 $\pm$ 0.10, r-i = 0.25$\pm$0.06, i-Z = -0.27 $\pm$ 0.10, and Y-J = 0.41 $\pm$ 0.10. 2024 YR$_4$ has a spectrum that best matches R-type and Sa-type asteroids and a diameter of $\sim$30-65 m using our measured absolute magnitude of 23.9 $\pm$ 0.3 mag, and assuming an albedo of 0.15-0.4. The lightcurve of 2024 YR$_4$ shows $\sim$0.4 mag variations with a rotation period of $\sim$1170 s. We use photometry of 2024 YR$_4$ from Gemini and other sources taken between 2024 December to 2025 February to determine the asteroid's spin vector and shape, finding that it has an oblate, $\sim$3:1 a:c axial ratio and a pole direction of $\lambda$, $\beta$ = $\sim$42$^{\circ}$, $\sim$-25$^{\circ}$. Finally, we compare the orbital elements of 2024 YR$_4$ with the NEO population model and find that its most likely sources are resonances between the inner and central Main Belt.

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arXiv2025

Confined tumbling state as the origin of the excess of slowly rotating asteroids

The rotational distribution of asteroids as a function of their size is used {as a diagnostic of} their physical properties and evolution. Recent photometric surveys from the Gaia mission, allowing observation of asteroids with long spin periods (for example $\geq 24$h), found an excessive group of slow rotators and a gap separating them from faster rotators, which is unexplained by current theories. Here we developed an asteroid rotational evolution model capable of reproducing the observed distribution. {We suggest that this distribution is regulated by the competition between collisions and internal friction dampening of "tumblers" -asteroids with unstable rotation vectors, and that the slow rotator group is mainly populated by tumblers.} {We constrain the product of the rigidity and quality factor, which relates to the body's viscosity, to $\mu Q \sim 4 \times 10^9~$Pa. This number, two orders of magnitude smaller than the one assumed for monolithic boulders,} implies that {rubble pile} asteroids could have a porous structure or a thick regolith layer, and undergo stronger tidal effects.

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arXiv2025

Keck and Gemini characterization of $Hayabusa2\#$ rendezvous target 1998 KY$_{26}$

Near-earth object (NEO) 1998 KY$_{26}$ is a target of the $Hayabusa2\#$ spacecraft, which it will rendezvous with in July 2031. The asteroid is a rapid rotator and has a large out-of-plane nongravitational acceleration. We present deep $g$ and $R$ band imaging obtained with the Keck I/Low Resolution Imaging Spectrometer and visible spectroscopy from Gemini North/Gemini Multi-Object Spectrograph taken of 1998 KY$_{26}$ on 2024 June 8-9 when the asteroid was $\sim$0.037 au from the Earth. The asteroid lacks evidence of a dust coma in the deep images and its spectrum most closely resembles Xe-type asteroids, possessing a spectral slope of 6.71$\pm$0.43 $\%$ 100 nm$^{-1}$, and colors $g$-$r$ = 0.63$\pm$0.03, $r$-$i$ = 0.15$\pm$0.03, $i$-$z$ = 0.05$\pm$0.04, and implies a diameter of $\sim$10 m. From our images, we compute a 3$\sigma$ upper limit on the dust production of 1998 KY$_{26}$ of $<$10$^{-5}$ kg s$^{-1}$, $<$10$^{-2}$ kg s$^{-1}$, and $<$10$^{-1}$ kg s$^{-1}$ assuming $\mathrm{\mu}$m, mm, and cm size dust particles. Additionally, we compare the orbit of 1998 KY$_{26}$ and large nongravitational parameters asteroids to NEO population models and find that the majority, including 1998 KY$_{26}$, likely originated from the inner Main Belt, while the second most numerous group originates from the outer Main Belt, followed by a third group originating from the Jupiter Family Comet population. Given its inner Main Belt origin, its Xe-type spectrum, and rapid rotation, we hypothesize that the nongravitational acceleration of 1998 KY$_{26}$ may be caused by the shedding of large dust grains from its surface due to its rotation rather than H$_2$O vapor outgassing.

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arXiv2024

The Yarkovsky effect on the long-term evolution of binary asteroids

We explore the Yarkovsky effect on small binary asteroids. While significant attention has been given to the binary YORP effect, the Yarkovsky effect is often overlooked. We develop an analytical model for the binary Yarkovsky effect, considering both the Yarkovsky-Schach and planetary Yarkovsky components, and verify it against thermophysical numerical simulations. We find that the Yarkovsky force could change the mutual orbit when the asteroid's spin period is unequal to the orbital period. Our analysis predicts new evolutionary paths for binaries. For a prograde asynchronous secondary, the Yarkovsky force will migrate the satellite towards the location of the synchronous orbit on ~100 kyr timescales, which could be faster than other synchronization processes such as YORP and tides. For retrograde secondaries, the Yarkovsky force always migrates the secondary outwards, which could produce asteroid pairs with opposite spin poles. Satellites spinning faster than the Roche limit orbit period (e.g. from ~4h to ~10h) will migrate inwards until they disrupt, reshape, or form a contact binary. We also predict a short-lived equilibrium state for asynchronous secondaries where the Yarkovsky force is balanced by tides. We provide calculations of the Yarkovsky-induced drift rate for known asynchronous binaries. If the NASA DART impact broke Dimorphos from synchronous rotation, we predict that Dimorphos's orbit will shrink by \dot a ~ 7 cm/yr, which can be measured by the Hera mission. We also speculate that the Yarkovsky force may have synchronized the Dinkinesh-Selam system after a possible merger of Selam's two lobes.

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arXiv2024

EL meteorites do date the giant planet instability

In our recent work, we combined dynamical simulations, meteoritic data and thermal models as well as asteroid observations to argue that the current parent body of the EL meteorites was implanted into the asteroid belt not earlier than 60 Myr after the beginning of the Solar System and that the most likely capture mechanism was the giant planet orbital instability. In the study "The link between Athor and EL meteorites does not constrain the timing of the giant planet instability" that appeared in arXiv, Izidoro and collaborators argue that the implantation of Athor into the asteroid belt does not necessarily require that the giant planet orbital instability occurred at the implantation time. Here we provide further arguments that, in the end, the giant planet instability is still the most likely dynamical process to implant asteroid Athor into the asteroid main belt between 60 and 100 Myr after the beginning of the Solar System.

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arXiv2024

NEOMOD 3: The Debiased Size Distribution of Near Earth Objects

Our previous model (NEOMOD2) for the orbital and absolute magnitude distribution of Near Earth Objects (NEOs) was calibrated on the Catalina Sky Survey observations between 2013 and 2022. Here we extend NEOMOD2 to include visible albedo information from the Wide-Field Infrared Survey Explorer. The debiased albedo distribution of NEOs can be approximated by the sum of two Rayleigh distributions with the scale parameters p_V,dark=0.03 and p_V,bright=0.17. We find evidence for smaller NEOs having (on average) higher albedos than larger NEOs; this is likely a consequence of the size-dependent sampling of different main belt sources. These inferences and the absolute magnitude distribution from NEOMOD2 are used to construct the debiased size distribution of NEOs. We estimate 830+/-60 NEOs with diameters D>1 km and 20,000+/-2,000 NEOs with D>140 m. The new model, NEOMOD3, is available via the NEOMOD Simulator -- an easy-to-operate code that can be used to generate user-defined samples (orbits, sizes and albedos) from the model.

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arXiv2024

Discovery of the first olivine-dominated A-type asteroid family

The classical theory of differentiation states that due to the heat generated by the decay of radioactive elements, some asteroids form an iron core, an olivine-rich mantle, and a crust. The collisional breakup of these differentiated bodies is expected to lead to exposed mantle fragments, creating families of newly-formed asteroids. Among these new objects, some are expected to show an olivine-rich composition in spectroscopic observations. However, several years of spectrophotometric surveys have led to the conclusion that olivine-rich asteroids are rare in the asteroid main belt, and no significant concentration of olivine-rich bodies in any asteroid family has been detected to date. Using ESA's Gaia DR3 reflectance spectra, we show that the family (36256) 1999 XT17 presents a prominence of objects that are likely to present an olivine-rich composition (A-type spectroscopic class). If S-complex asteroids as the second most prominent spectroscopic class in the family are real family members, then arguably the 1999 XT17 family has originated from the break-up of a partially differentiated parent body. Alternatively, if the S-complex asteroids are interlopers, then the 1999 XT17 family could have originated from the breakup of an olivine-rich body. This body could have been part of the mantle of a differentiated planetesimal, which may have broken up in a different region of the Solar System, and one of its fragments (i.e. the parent body of the 1999 XT17 family) could have been dynamically implanted in the main belt.

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arXiv2023

Gaia view of primitive inner-belt asteroid families: Searching for the origins of asteroids Bennu and Ryugu

Near-Earth asteroids Ryugu and Bennu, were visited, characterised, and sampled by the Hayabusa2 and OSIRIS-REx missions: remote sensing data and sample return analysis showed that both asteroids have primitive, hydrated and organic-rich compositions. The dark families of the inner main belt (IMB) that belong to the spectroscopic C-complex have been claimed to be the sources of both Ryugu and Bennu. Hence, there has been large effort to characterise them. Here we used the Gaia Data Release 3 (DR3) asteroid reflectance spectra to investigate the 11 known IMB C-complex families (Chaldaea, Chimaera, Clarissa, Erigone, Eulalia, Klio, Polana, Primordial, Sulamitis, Svea, Tamara). For each family, we extracted the family members that have known geometric visible albedo values and Gaia DR3 data and we created an average reflectance spectrum per family between 370 and 950 nm. The average DR3 reflectance spectra of each family were compared with the previous literature data and to Bennu's and Ryugu's spectra. We found that DR3 reflectance spectra of the IMB C-complex families are in general consistent with previous findings with the only exception of the Svea family. We also showed that the Polana and the Eulalia families can be distinguished in the wavelength region 370 - 500 nm. Among all the IMB C-complex families, we determined that the average reflectance spectra of the Eulalia and Polana families are the most similar to those of Bennu and Ryugu, respectively. In particular, Eulalia family's average spectrum is a good match to Bennu's in the wavelength range 450 - 800 nm, while beyond 800 nm the spectrum of Bennu is bluer than that of Eulalia. Moreover, the spectrum of the Polana family has the smallest discrepancy against the spectrum of Ryugu, although this match is formally unsatisfactory (reduced chi^2 ~ 1.9).

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