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Chrysa Avdellidou

Publications and source records attributed to Chrysa Avdellidou.

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

NSF-DOE Vera C. Rubin Observatory Observations of Interstellar Comet 3I/ATLAS (C/2025 N1)

We report on the observation and measurement of astrometry, photometry, morphology, and activityof the interstellar object 3I/ATLAS, also designated C/2025 N1 (ATLAS) with the NSF-DOE Vera C. Rubin Observatory. Comet 3I/ATLAS, the third known interstellar object, was discovered on UT 2025 July 1. Rubin Observatory had coincidentally collected images of the object's region of the sky during routine commissioning. Facilitated by Rubin's high resolution and large aperture, we successfully recovered object detections from Rubin observations spanning UT 2025 June 21 (10 days before discovery, when 3I/ATLAS was 4.5 au from the Sun) through the date of discovery, and we acquired additional images through UT 2025 July 20 as part of commissioning. We measure on-sky locations of 3I/ATLAS in Rubin ugrizy bands, with a typical precision of about 70 mas, and briefly describe the reason this is coarser than our measured static source astrometric precision of about 3 mas in Rubin images. We measure grizy magnitudes of 3I/ATLAS photometry at about 0.01 mag precision, detecting no short-term photometric variability above 0.01 mag. We derive an estimated near-nucleus dust-to-nucleus scattering cross-section ratio of eta >= 13 on UT 2025 July 2 based on Rubin photometry and an upper limit nucleus size computed from Hubble Space Telescope observations. We find Rubin colors of g - r = (0.657 +/- 0.013) mag, r - i = (0.235 +/- 0.018) mag, i - z = (0.147 +/- 0.042) mag, z - y = (0.047 +/- 0.052) mag. These data represent the earliest observations of this object by a large (>=8-meter class) telescope and illustrate the type of measurements (and discoveries) Rubin's Legacy Survey of Space and Time (LSST) will begin to provide after it begins in early 2026.

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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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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

The Massalia asteroid family as the origin of ordinary L chondrites

Studies of micrometeorites in mid-Ordovician limestones and Earth's impact craters indicate that our planet witnessed a massive infall of ordinary L chondrite material 466 million years (My) ago (Heck et al. 2017, Schmieder & Kring 2020, Kenkmann 2021) that may have been at the origin of the first major mass extinction event (Schmitz et al. 2019). The breakup of a large asteroid in the main belt is the likely cause of this massive infall. In modern times, material originating from this breakup still dominates meteorite falls (>20% of all falls) (Swindle et al. 2014). Here, we provide spectroscopic observations and dynamical evidence that the Massalia collisional family is the only plausible source of this catastrophic event and of the most abundant class of meteorites falling on Earth today. It is suitably located in the inner belt, at low-inclination orbits, which corresponds to the observed distribution of L-chondrite-like near-Earth objects (NEOs) and of interplanetary dust concentrated at 1.4 degrees (Sykes 1990, Reach et al. 1997).

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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

Multicolor Photometry of Tiny Near-Earth Asteroid 2015 RN$_{35}$ Across a Wide Range of Phase Angles: Possible Mission Accessible A-type Asteroid

Studying small near-Earth asteroids is important to understand their dynamical histories and origins as well as to mitigate the damage of the asteroid impact to the Earth. We report the results of multicolor photometry of the tiny near-Earth asteroid 2015 RN$_{35}$ using the 3.8 m Seimei telescope in Japan and the TRAPPIST-South telescope in Chile over 17 nights in 2022 December and 2023 January. We observed 2015 RN$_{35}$ across a wide range of phase angles from 2$^{\circ}$ to 30$^{\circ}$ in the $g$, $r$, $i$, and $z$ bands in the Pan-STARRS system. These lightcurves show that 2015 RN$_{35}$ is in a non-principal axis spin state with two characteristic periods of $1149.7\pm0.3$ s and $896.01\pm0.01$ s. We found that a slope of a visible spectrum of 2015 RN$_{35}$ is as red as asteroid (269) Justitia, one of the very red objects in the main belt, which indicates that 2015 RN$_{35}$ can be classified as an A- or Z-type asteroid. In conjunction with the shallow slope of the phase curve, we suppose that 2015 RN$_{35}$ is a high-albedo A-type asteroid. We demonstrated that surface properties of tiny asteroids could be well constrained by intensive observations across a wide range of phase angles. 2015 RN$_{35}$ is a possible mission accessible A-type near-Earth asteroid with a small $Δv$ of 11.801 km s$^{-1}$ in the launch window between 2030 and 2035.

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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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arXiv2023

Extending Lunar Impact Flash Observations into the Daytime with Short-Wave Infrared

Lunar impact flash (LIF) observations typically occur in R, I, or unfiltered light, and are only possible during night, targeting the night side of a 10-60% illumination Moon, while >10° above the observers horizon. This severely limits the potential to observe, and therefore the number of lower occurrence, high energy impacts observed is reduced. By shifting from the typically used wavelengths to the J-Band Short-Wave Infrared, the greater spectral radiance for the most common temperature (2750 K) of LIFs and darker skies at these wavelengths enables LIF monitoring to occur during the daytime, and at greater lunar illumination phases than currently possible. Using a 40.0 cm f/4.5 Newtonian reflector with Ninox 640SU camera and J-band filter, we observed several stars and lunar nightside at various times to assess the theoretical limits of the system. We then performed LIF observations during both day and night to maximise the chances of observing a confirmed LIF to verify the methods. We detected 61 >5σ events, from which 33 candidate LIF events could not be discounted as false positives. One event was confirmed by multi-frame detection, and by independent observers observing in visible light. While this LIF was observed during the night, the observed signal can be used to calculate the equivalent Signal-to-Noise ratio for a similar daytime event. The threshold for daylight LIF detection was found to be between Jmag=+3.4+-0.18 and Jmag=+5.6+-0.18 (Vmag=+4.5 and Vmag=+6.7 respectively at 2750 K). This represents an increase in opportunity to observe LIFs by almost 500%.

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arXiv2023

Gaia search for early-formed andesitic asteroidal crusts

Context. Andesitic meteorites are among the oldest achondrites known to date. They record volcanic events and crust formation episodes in primordial planetesimals that took place about 4.565 Myr ago. However, no analogue for these meteorites has been found in the asteroid population to date. Aims. We searched for spectroscopic analogues of the andesitic meteorite Erg Chech 002 in the asteroid population using the Gaia DR3 spectral dataset. Methods. In order to identify which asteroids have the most similar spectrum to Erg Chech 002, we first determined the spectral parameters of Gaia DR3 asteroids (spectral slope and Band I depth) and compared them to the spectral parameters of different samples of the meteorite. In addition, we performed a spectral curve matching between Erg Chech 002 and Gaia DR3 asteroid data, and we compared the results of both methods. Results. We found that 51 main-belt asteroids have a visible spectrum similar to the one of Erg Chech 002, and 91 have a spectrum similar to the space-weathered spectra of the meteorite, corresponding to 0.08 and 0.15% of the whole Gaia DR3 dataset of asteroids with spectra, respectively. The asteroids that best match the laboratory samples of the meteorite are mostly located in the inner main belt, while the objects matching the space-weathered meteorite models show slightly more scattering across the belt. Conclusions. Despite the fact that we find asteroids that potentially match Erg Chech 002, these asteroids are extremely rare. Moreover, a visible spectrum alone is not completely diagnostic of an Erg Chech 002-like composition. Near-infrared spectra will be important to confirm (or rule out) the spectral matches between Erg Chech 002 and the candidate asteroid population.

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arXiv2022

PyNAPLE: Lunar Surface Impact Crater Detection

In the last 20 years, over 600 impact flashes have been documented on the lunar surface. This wealth of data presents a unique opportunity to study the meteoroid flux of the Earth-Moon environment, and in recent years the physical properties of the impactors. However, other than through serendipitous events, there has not been yet a systematic search and discovery of the craters associated to these events. Such a meteoroid-crater link would allow us to get insight into the crater formation via these live observations of collisions. Here we present the PyNAPLE (Python NAC Automated Pair Lunar Evaluator) software pipeline for locating newly formed craters using the location and epoch of an observed impact flash. We present the first results from PyNAPLE, having been implemented on the 2017-09-27 impact flash. A rudimentary analysis on the impact flash and linked impact crater is also performed, finding that the crater's ejecta pattern indicates an impact angle between 10-30 degree, and although the rim-to-rim diameter of the crater is not resolvable in current LRO NAC images, using crater scaling laws we predict this diameter to be 24.1-55.3 m, and using ejecta scaling predict a diameter of 27.3-37.7 m. We discuss how PyNAPLE will enable large scale analyses of sub-kilometer scale cratering rates and refinement of both scaling laws, and the luminous efficiency.

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arXiv2022

Spectral evolution of dark asteroid surfaces induced by space weathering over a decade

The surface of airless bodies like asteroids in the Solar System are known to be affected by space weathering. Experiments simulating space weathering are essential for studying the effects of this process on meteorite samples, but the problem is that the time spent to reproduce space weathering in these experiments is billions of times shorter than the actual phenomenon. In December 2010, the T-type asteroid 596 Scheila underwent a collision with a few-tens-of-meters impactor. A decade later, there is an opportunity to study how the surface layer of this asteroid is being altered by space weathering after the impact. To do so, we performed visible spectrophotometric and near-infrared spectroscopic observations of 596 Scheila. The acquired spectrum is consistent with those observed shortly after the 2010 impact event within the observational uncertainty range. This indicates that the surface color of dark asteroids is not noticeably changed by space weathering over a 10-year period. This study is the first to investigate color changes due to space weathering on an actual asteroid surface in the Solar System. Considering that fresh layers are regularly created on asteroid surfaces by collisions, we suggest a genetic link between D/T-type and dark (low albedo) X-complex asteroids and very red objects such as 269 Justitia, 732 Tjilaki (and 203 Pompeja). New observations show that 203 Pompeja has a X-type-like surface, with some local surface areas exhibiting a very red spectrum.

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arXiv2021

Very weak carbonaceous asteroid simulants I: mechanical properties and response to hypervelocity impacts

The two on-going sample return space missions, Hayabusa2 and OSIRIS-REx are going to return to Earth asteroid regolith from the carbonaceous near-Earth asteroids Ryugu and Bennu. The two main processes that lead to regolith production are the micrometeorite bombardment and the thermal cracking. Here we report the production of a weak simulant material, analogue to carbonaceous meteorites with a CM-like composition, following the preliminary compositional results for Bennu and Ryugu. This asteroid simulant has compressive and flexural strength 1.8+/-0.17 and 0.7+/-0.07 MPa, respectively. The thermal conductivity (in air) of the simulant at room temperature is between 0.43 and 0.47 W/m/K. In order to distinguish the type of regolith that is produced by each of these processes, we present and discuss the results of the experimental campaign focused on laboratory hypervelocity impacts, using the 2-stage light-gas gun of the University of Kent, that mimic the micrometeorite bombardment. We find that this process produces both monomineralic and multimineralic fragments, resulting in a difficulty to distinguish the two processes, at least on these weak materials.

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arXiv2021

Impacts on the Moon: analysis methods and size distribution of impactors

We are preparing a telescope system to carry out a survey of detection and analysis of lunar impact flashes. In the framework of this project, here we present all necessary methods to automatically identify these luminous events, their lunar impact coordinates, the origin of the impacting meteoroids, as well as the estimation of their physical properties such as mass and size. We tested our methods against confirmed impact events and constructed the meteoroid size frequency distribution of impactors using literature data of the last 20 years. In addition, we present the first lunar impact event observed from the Observatoire de la Cote d'Azur that was detected during the testing phase of our project.

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