SB1

Our understanding of Solar System family asteroids has been significantly widened by space surveys primarily targeted to exoplanet detections. In K2 and TESS fields, many asteroids passed through, being a basis of continuous sateroid photometry covering several basis. This enabled the proof
of the high fraction of slow rotators (period>30 hours) in asteroid families (30%), non-family MB asteroids (35%), the Hilda group (39%) and the Trojan swarms (25%). High ratio of extremely slow rotators (P > 100 hr) in the Hilda group is (18%) is unique in the Solar System. 

We found a family-specific amplitude and/or period distribution only in some asteroid families (Hungaria, Maria, Juno, Eos, Eucharis, and Alauda). Older families tend to contain a larger fraction of more spheroidal, low-amplitude asteroids. The rotation period distributions are different in the cores and outskirts of the Flora and Maria families, while the Vesta, Eos, and Eunomia families lack this feature. We also confirm that very fast spinning 
asteroids are close to spherical (or spinning top shapes), and minor planets rotating slower than ≈11 h are also more spherical than asteroids in the 4-8 h period range and this group is expected to contain the most elongated bodies. 

Despite a previously suggested mixed origin of Hildas from the MB and the Trojan swarms, we revealed no differences in the photometric properties between the taxonomically different R and LR Hildas: the entire Hilda group highly resembles the Trojans for rotational properties. 

How to cite: Szabó, G.: Rotational properties of MB family asteroids, Hildas, and Trojans, based on K2 and TESS observations, Europlanet Science Congress 2022, Granada, Spain, 18–23 Sep 2022, EPSC2022-293, https://doi.org/10.5194/epsc2022-293, 2022.

Colors have been commonly used by researchers to assign taxonomic class to asteroids. Furthermore, the optical design of future space surveys should account for a large number of incidental asteroid observations that they will likely make. It is thus crucial to consider a use of an optimal filter setup for asteroid taxonomic classification. Following the work from Klimczak et al. 2021 which compared different machine learning algorithms (Naive Bayes, Logistic Regression, Support Vector Machine (SVM), Gradient-boosting, Multilayer Perceptrons) on two different parameter sets: principal component directions (PCA) and reflectance values spaced 0.05μm in the 0.45-2.5μm range and spectral slope, we extend this analysis to reflectance colors.  We aim to study the most efficient way to link colors to the Bus-DeMeo taxonomy and obtain a set of narrow band filters that should be used to correctly detect the taxonomic type of an object. 

The set of features used in this work consists of 35 reflectance colors that were selected across the wide range of spectroscopic measurements. All aforementioned machine learning methods are trained to predict taxonomic types on this set, and Feature Selection is performed to assess the importance of individual features and decrease the redundancy of the set. 

We find that Multilayer Perceptron and Support Vector Machines provide the best results on the whole feature set, with 85% balanced accuracy for taxonomic types and 93% for complexes. These results slightly outperform the results from our previous work. Furthermore, we find that satisfactory results can be obtained by reducing the feature set to top 5 features for taxonomic types (retaining 80% balanced accuracy), and top 3 features for complexes (retaining 89% balanced accuracy).

This work has been supported by grant No. 2017/25/B/ST9/00740 from the National Science Centre, Poland.

How to cite: Klimczak, H., Kotłowski, W., Oszkiewicz, D., DeMeo, F., Kryszczyńska, A., Wilawer, E., and Kwiatkowski, T.: Optimization of future multi-filter surveys towards asteroid characterisation, Europlanet Science Congress 2022, Granada, Spain, 18–23 Sep 2022, EPSC2022-796, https://doi.org/10.5194/epsc2022-796, 2022.

Introduction. The NEO Rapid Observation, Characterization and Key Simulations (NEOROCKS) project is funded (2020-2023) through the H2020 European Commission programme to improve our knowledge on near-Earth objects by connecting expertise in performing small body astronomical observations and the related modelling needed to derive their dynamical and physical properties. The Instituto de Astrofísica de Canarias (IAC), and in particular members of the Solar System Group, participate in the NEOROCKS project and currently are devoted to one specific task: to collect observational data, mainly in the visible and near-infrared wavelength regions, of NEAs that have been observed in the past using the Arecibo Planetary Radar. In this work we present preliminary results, focusing on those targets for which the signal-to-noise ratio is satisfactorily high.

Observations. Our observations include spectroscopy, color photometry and lightcurves. They are performed using the facilities located at the Observatorios de Canarias (OOCC), including the El Teide Observatory in the island of Tenerife and the El Roque de los Muchachos Observatory in the island of La Palma. Visible and near-infrared spectra are mainly obtained using the 10.4-m Gran Telescopio de Canarias (GTC) and its visible (OSIRIS) and near-infrared (EMIR) spectrographs. We also use the ALFOSC spectrograph at the 2.5-m Nordic Optical Telescope (NOT). Visible color photometry is obtained using the MuSCAT2 instrument at the 1.5-m Telescopio Carlos Sánchez (TCS). The setup allows us to obtain simultaneous imaging in the g, r, i, and z_s visible bands. Time-series photometry in the visible is obtained using several telescopes, including the 46-cm TAR2, 80-cm IAC-80, and 1-m Jacobus Kapteyn Telescope (JKT).

Results. Spectra in the visible and/or the near-infrared wavelengths, as well as color photometry in the visible, allow us to taxonomically classify the targets and to infer their composition. In the case of having no albedo measurements for any given object, we can also use the taxonomy to have an estimation of the albedo based on the spectral class, and therefore determine the size of the asteroid. Lightcurves allow us to both get the asteroid rotational period and, together with radar data, to obtain the shape and the spin axis orientation of the target. In this way, a full characterization can be obtained for every asteroid observed within this program. So far, we have obtained spectra/colors/lightcurves in the visible for more than 100 NEAs. In this work, we present our most updated results.

Acknowledgements. This project has received funding from the European Union’s Horizon 2020 research and innovation programme under grant agreement No 870403.

How to cite: Medeiros, H., de León, J., Licandro, J., Popescu, M., Morate, D., and Pinilla-Alonso, N. and the Arecibo Planetary Radar Team*, and the NEOROCKS Team**: NEOROCKS characterization programme of near-Earth asteroids previously observed with radar, Europlanet Science Congress 2022, Granada, Spain, 18–23 Sep 2022, EPSC2022-570, https://doi.org/10.5194/epsc2022-570, 2022.

Primitive asteroids (PAs) are characterized by dark surfaces (albedo < 10%) dominated by carbon compounds. Their reflectance spectra are similar to those of carbonaceous chondrites (CCs), the most pristine meteorites in our records, abundant in hydrated minerals and organics. Studying these life-forming materials in PAs and CCs is important to answer how water and life appeared on Earth.

PAs present rather featureless spectra in visible and near-infrared wavelengths (from 0.5 to 2.5 microns). The most diagnostic and reliable region to study hydrated mineralogies and organics is the 3 microns region. However, observing at those wavelengths is extremely complicated using ground-based telescopes due to Earth's atmosphere, and so, the 3-microns feature can only be appropriately studied using space telescopes (e.g. AKARI). Another feature in visible wavelengths around 0.7 µm, thus accessible from the Earth, is related to the Fe2+ Fe3+ iron transition in hydrated mineralogies (Vilas 1994, Fornasier et al. 2014, Morate et al. 2016). However, this band is shallow. Hiroi et al (1998) have proposed a correlation between the 3 microns band and the UV absorption based on the meteorite spectra. 

In our work, we aim to explore the near UV (NUV hereafter) behavior of PAs and try to relate it with the main characteristics in the visible (0.7 micron band and slope). To accomplish this objective we have observed and explored spectral data for more than a hundred primitive asteroids with different taxonomies using the 3.58-m Telescopio Nazionale Galileo and the 2.54-m Isaac Newton Telescope located at the Roque de Los Muchachos Observatory. All the spectra go down to ~0.35 microns (near-UV or NUV). The ground-based reflectance spectroscopy in NUV needs special cautions such as airmass, and solar analogs (Tatsumi et al. accepted). In addition, we have explored the Hubble Space Telescope archive thanks to the Archival Research Visitor Program from ESA, finding also some primitive asteroids observed at UV. We also selected ~100 PAs from the MoOJA catalog (Morate et al. 2021), that have 5 filters between 0.35 and 0.55 microns and other 7 from 0.55 to 1 microns. This set of filters allows us to obtain information about how strong is the NUV absorption, to characterize the 0.7-micron band, and to compute several spectral slopes.

Results: we have found a correlation of 77% between the difference of spectral slopes between 0.4 - 0.55 microns and 0.55-0.7 microns (associated with the absorption in the UV) and the difference of spectral slopes between 0.55 - 0.7 microns and 0.7-0.9 microns (associated with iron transition at 0.7 microns), see Figure 1. Therefore, this drop in reflectance in the NUV can be used as a proxy for the phyllosilicates to measure the hydration degree of asteroids. Moreover, there are Fe-rich and Mg-rich phases among phyllosilicates, which reflect the amount of water present during their formation. On other hand, we have found a way to describe the beginning of the NUV drop, and among different taxonomies, there is a difference in the wavelength statistically significant, see Figure 2.

Gaia DR3 will provide thousands of low-resolution slit-less spectra of asteroids in the range of 0.35 - 0.90 microns before the meeting. This will constitute the largest dataset of asteroid spectra down to the NUV and we are going to also present how the thousands of asteroid spectra look like in our spectral slope space.

Figure 1. Slope change at 0.55 microns (computed as slope between 0.39 and 0.55 microns minus slope between 0.55 and 0.7) versus slope change at 0.7 microns (computed as slope between 0.55 and 0.7 minus slope between 0.7 and 0.9). The Pearson correlation coeficient between both variables is 0.77.

Figure 2. Histogram for the wavelength where the drop in reflectance downwards UV wavelengths begins for C, B, G and F taxonomies. We can see 2 main groups: one around 0.4 microns composed by F and B types and the other around 0.55 containing mainly C and G types.

REFERENCES

Fornasier, S., Lantz, C., Barucci, M. A., & Lazzarin, M. 2014, Icarus, 233, 163

Hiroi, T. and Zolensky, E.M.: 1998, Antarctic Meteorites XXIII; 23, 30.

Morate, D., de León, J., De Prá, M., et al. 2016, A&A, 586, A129

Tatsumi, E., Tinaut-Ruano, F., de León, J., et al. 2022, A&A, accepted

Vilas, F. 1994, Icarus, 111, 456

How to cite: Tinaut-Ruano, F., Tatsumi, E., de León, J., and Morate, D.: Exploring the near-UV for primitive asteroids using ground-based observations, space telescopes, a survey-like catalog, and following up with Gaia, Europlanet Science Congress 2022, Granada, Spain, 18–23 Sep 2022, EPSC2022-1049, https://doi.org/10.5194/epsc2022-1049, 2022.

Using multi-directional measurements of the Transiting Exoplanet Survey Satellite we have been able to perform analysis on small bodies in the Solar System. In order to validate a purely TESS-based shape and spin-axis reconstruction modelling we determined the spin axis of about forty objects, selected from our large light curve sample. We chose those targets that had been measured in at least three TESS sectors and showed an amplitude variation large enough to constraint the direction of the spin axis.  In our simple model the asteroid's shape is approximated with a triaxial ellipsoid, rotating around its shortest axis, with a fixed spin axis direction. Seen from different directions, the light curves and amplitudes would also be different, and we minimize the difference between the predicted and measured amplitudes to obtain the best fitting spin axis direction (lambda_p, beta_p) and shape parameters. Our spin axis solutions are compared to those in the DAMIT database which are based on multi-epoch, mainly ground-based observations. This benchmark study will indicate the capabilities in obtaining shape and spin axis solutions from large surveys. Extracting this information for several such asteroids we can obtain shape and spin axis direction distributions which will be used to infer the formation and dynamics of the asteroid belt using formation and collisional evolution models, for a significantly larger number of targets then before, and using high quality light curve data.  

Figure 1: Light curves of the asteroid (4717) Kaneko observed in six different sectors of TESS

Figure 2: χ² contours obtained from the comparision of observed and predicted light curve amplitudes for (4717) Kaneko. The lowest contours represent our best fitting spin axis solutions in ecliptic coordinates. Circles mark the spin axis solutions provided by DAMIT.

How to cite: Nóra, T., Pál, A., and Kiss, C.: Spin-axis and rotation of small bodies using multi-directional measurements of the Transiting Exoplanet Survey Satellite, Europlanet Science Congress 2022, Granada, Spain, 18–23 Sep 2022, EPSC2022-1225, https://doi.org/10.5194/epsc2022-1225, 2022.

Abstract

Until recently, only three large main belt asteroids, Ceres, Vesta and Lutetia, had been imaged with a high level of detail, as they were visited by the space missions Dawn and Rosetta of NASA and the European Space Agency, respectively. The previously small number of detailed observations of asteroids meant that, until now, key characteristics such as their 3D shape or density had remained largely unknown. Between 2017 and 2019, we have been filling this gap by conducting a high-angular-resolution imaging survey of 42 large main-belt asteroids with VLT/SPHERE (ESO large programme; PI: P. Vernazza; ID: 199.C-0074), sampling the main compositional classes. These observations have allowed to cast some light on the following fundamental questions:

– What is the diversity in shape among large asteroids and are the shapes close to equilibrium?
– How do large impacts affect asteroid shape?
– What is the bulk density of large asteroids and is there a relationship with their surface composition? Is there any evidence of differentiation among those bodies?
– Is the density of those bodies that are predicted to be implanted bodies from the outer Solar System (P/D-types) compatible with that of small (D ≤ 300 km) trans-Neptunian objects?
– What physical properties drive the formation of companions around large asteroids?

Importantly, our survey along with previous observations provides evidence in support of the possibility that some C-complex bodies could be intrinsically related to IDP-like P- and D-type asteroids, representing different layers of a same body (C: core; P/D: outer shell). We therefore propose that P/ D-types and some C-types may have the same origin in the primordial trans-Neptunian disk. The main belt would thus host a population of former TNOs much more important than the one previously considered, consisting solely of P and D-type bodies.

Here, we will present an overview of the results obtained from this survey ([1]) with a specific focus on the origin of a large fraction of the asteroid belt (typically C, P and D-type bodies).

References

[1] Vernazza, P., Ferrais, M., Jorda, L., et al. VLT/SPHERE imaging survey of the largest main-belt asteroids: Final results and synthesis. A&A 654, 2021.

How to cite: Vernazza, P., Ferrais, M., Jorda, L., Hanus, J., Carry, B., Marsset, M., Brož, M., and Fetick, R. and the HARISSA team: VLT/SPHERE imaging survey of D>100 km asteroids: Final results and synthesis, Europlanet Science Congress 2022, Granada, Spain, 18–23 Sep 2022, EPSC2022-103, https://doi.org/10.5194/epsc2022-103, 2022.

Introduction

Asteroid families generated by the collisional fragmentation of a common parent body have been identified using clustering methods of asteroids in their proper orbital element space (Broz & Morbidelli 2013; Tsirvoulis et al. 2018; Dermott et al. 2021). However, there is growing evidence that some of the real families are larger than the corresponding cluster of objects in orbital elements, as well as there are families that escaped identification from clustering methods (Milani et al. 2014). An alternative method has been developed by Bolin et al. (2017); Delbo et al. (2017), in order to identify collisional families from the correlation between the asteroid fragment sizes and their proper semimajor axis distance from the family center (V-shape). This method has been shown to be effective in the cases of the very diffused families that have formed Gyrs ago. Based on this method, a 4 Gyr-old (so-called primordial) collisional family of the inner main belt has been identified consisting of low-albedo asteroids (Delbo et al. 2017). The theory of asteroid family evolution predicts that there is an excess on retrograde asteroids in the inward side of the family’s V-shape. For this reason, photometric observations were performed in order to construct their rotational light curves and determine their shape and spin state.

Dataset and Observations

We combined data of asteroid lightcurves that we collected from the databases, sparse photometric data obtained from different surveys and existing shape models. Aiming to enlarge our input dataset used for the shape modelling, which would potentially lead to new and improved shape solutions, we performed additional ground-based photometric observations.

An international observing campaign has been initiated in the framework of our international initiative called Ancient Asteroids[1], aiming to collect dense photometric data for asteroids that belong to the oldest asteroid families (Athanasopoulos et al. 2021).

Method

The photometric datasets include both dense photometric data from ground-based facilities, as well as sparse data from several sky surveys and space missions. Appropriate analysis techniques were used for each type of dataset to extract the asteroid’s rotational light curve and use the convex inversion (CI) method developed by Kaasalainen & Torppa (2021); Kaasalainen et al. (2021). So far, the CI has been used to derive asteroid models for more than 3,460 asteroids that are stored in the DAMIT database.

Results

The spin state for 54 family members was determined by additionally using literature and sparse photometric data from ground and space observatories. Moreover, we measured rotation periods for 8 asteroids for the first time.

Combining new and literature data, we determined shapes and spin states for 54 asteroids that belong to the nominal population of the primordial family. This corresponds to 50% of the population in the sliver between the left-wing border of the Polana and the primordial family (see Fig. 1). Specifically, we calculated 23 new complete asteroid models, 16 revised and 8 new partial models, where 32 asteroids have retrograde rotation and 22 prograde.

Based on our analysis, we indicated 9 interlopers in the sample of 54 studied objects. From these 45 confirmed asteroid family members, 29 asteroids (65%) models have retrograde rotation and 16 prograde, including also the partial solutions.

Fig. 1: Panel A: The primordial family members are presented in proper semi-major axis vs. inverse diameter plane, along with the low albedo asteroids. Yellow diamond markers present members with known spin pole from the literature. Moreover, "plus", cross and square markers show the sources of dense lightcurves for these members. Panel B: The left side of the V-shape of the primordial family, where the red markers show the retrograde and blue markers the retrograde asteroids respectively.

Conclusion

We carried out a campaign of photometric observations of those asteroids that have been claimed to be members of one of the oldest collisional (primordial) families in the Solar System and we extract the lightcurves, spin state and shape for 45 members.

The statistical predominance of the retrograde spin poles is due to a physical process, as it was claimed by Delbo et al. 2017, namely formation as collisional fragments of a common parent body, a subsequent dynamical evolution driven by the Yarkovsky effect. The results of this research constitute corroborating evidence that the asteroids as members of a 4 Gry-old collisional family have a common origin, thus strengthening their family membership.

Acknowledgments

MD and CA acknowledge support from ANR “ORIGINS” (ANR-18-CE31-0014). This work is based on data provided by the Minor Planet Physical Properties Catalogue (MP3C) of the Observatoire de la Côte d’Azur. The research of JH has been supported by the Czech Science Foundation through grant 20-08218S. The work of OP has been supported by INTER-EXCELLENCE grant LTAUSA18093 from the Ministry of Education, Youth, and Sports. Support for T.W.-S.H. was provided by NASA through the NASA Hubble Fellowship grant HST-HF2-51458.001-A awarded by the Space Telescope Science Institute (STScI), which is operated by the Association of Universities for Research in Astronomy, Inc., for NASA, under contract NAS5-26555.

We thank the Las Cumbres Observatory and their staff for its continuing support of the ASAS-SN project, supported by the Gordon and Betty Moore Foundation through grant GBMF5490 to the Ohio State University and funded in part by the Alfred P. Sloan Foundation grant G-2021-14192 and NSF grant AST-1908570. Development of ASAS-SN has been supported by NSF grant AST-0908816, the Mt. Cuba Astronomical Foundation, the Center for Cosmology and AstroParticle Physics at the Ohio State University, the Chinese Academy of Sciences South America Center for Astronomy (CAS-SACA), the Villum Foundation, and George Skestos.

References

Athanasopoulos, D. et al. 2021, in European Planetary Science Congress Vol. 15, EPSC2021–335

Bolin, B. T. et al. 2017, Icarus, 282, 290

Brož, M. & Morbidelli, A. 2013, Icarus, 223, 844

Delbo’, M. et al. 2017, Science, 357, 1026

Dermott, S. F. et al. 2021, MNRAS, 505, 1917

Kaasalainen, M. & Torppa, J. 2001, Icarus, 153, 24

Kaasalainen, M. et al. 2001, Icarus, 153, 37

Milani, A. et al. 2014, Icarus, 239, 46

Tsirvoulis, G. et al. 2018, Icarus, 304, 14

How to cite: Athanasopoulos, D., Hanuš, J., Avdellidou, C., Bonamico, R., Delbo, M., Conjat, M., Ferrero, A., Gazeas, K., Rivet, J.-P., Sioulas, N., and Van Belle, G. and the Ancient Asteroids team: Asteroid spin-states of a 4 Gyr-old collisional family., Europlanet Science Congress 2022, Granada, Spain, 18–23 Sep 2022, EPSC2022-949, https://doi.org/10.5194/epsc2022-949, 2022.

The Hubble Space Telescope (HST) archives hide many unexpected treasures, such as trails of asteroids, showing a characteristic curvature due to the parallax induced by the orbital motion of the spacecraft. We have explored two decades of HST data for serendipitously observed asteroid trails with a deep learning algorithm on Google Cloud, called AutoML, trained on classifications from the Hubble Asteroid Hunter (www.asteroidhunter.org) citizen science project. 

The project was set up as a collaboration between the ESAC Science Data Centre, Zooniverse, and engineers at Google as a proof of concept to valorize the rich data in the ESA archives. I will present the first results from the project, finding 1,700 asteroid trails in the HST archives (Kruk et al., 2022). Their distribution on the sky is shown in Figure 1.

The majority of the asteroid trails (1,031) we found are faint (typically > 21 mag, see Figure 2) and do not match any entries in the Minor Planet Center database, thus likely  correspond to previously unidentified asteroids (see a few examples in Figure 3). We will argue that a combination of AI and crowdsourcing is an efficient way of exploring increasingly large datasets by taking full advantage of the intuition of the human brain and the processing power of machines. 

The second part of this project aims to analyze in detail these potentially new asteroids and use them to improve our current understanding of the size distribution of small-sized asteroids, and thus help constrain models of the evolution of our Solar System.

Taking into account Hubble’s motion around the Earth, the parallax effect can be computed to obtain the distance to the asteroids by fitting  simulated trajectories to the observed trails and obtaining the best fit (Evans et al. 1998). We show one example of a curve fit to the observed trail in Figure 4. Once we know the distance to the asteroids, we are able to obtain their absolute magnitudes and, combined with an assumed albedo, we can obtain their sizes. This method is also able to estimate an envelope for the asteroid's main orbital parameters. 

Given Hubble’s resolution and capability of reaching faint magnitudes, we expect that many of the new asteroids to be small-sized Main Belt asteroids (diameter <1 km), a population that is too faint and thus difficult to image from ground-based observatories. In addition, with the typical 30 min exposures of Hubble, some of these unknown objects show lightcurves that could be used to infer the rotation and shape of these asteroids, which is helpful for better assessing their type and origin.

This project may serve in the future as a “proof of concept” for an automated detection and analysis pipeline in large astronomical archives or surveys.

Figure 1: Distribution on the sky of the Solar System Objects (SSOs) identified in the HST images in Mollweide projection. The blue stars show the identified, known asteroids. The orange circles show the location of objects for which we did not find any associations with SSOs. The ecliptic is shown with red. The two gaps in this plot correspond to the Galactic plane, which was not observed by HST.

Figure 2: Distribution of apparent magnitudes for the SSOs identified in the HST images. The measured magnitudes for the identified objects (blue bars) and for the objects for which we did not find any associations with known SSOs (orange bars).

Figure 3: Examples of unidentified trails in HST observations. The HST observation IDs, clockwise, from the top left, are: j8pv03020, jds47w010, j9bk75010, icphg2010, jdrz23010, and jcng06010.

Figure 4: A trail fitting example using the parallax method. The distance solution yielding the best fit for a simulated parallax using HST trajectory is shown in red, in blue the observed trail.

How to cite: García Martín, P., Kruk, S., Popescu, M., Merín, B., Mahlke, M., Carry, B., Thomson, R., Karadag, S., Racero, E., Giordano, F., Baines, D., Durán, J., de Marchi, G., Laureijs, R., Stapelfeldt, K. R., and Evans, R. W.: Hubble Asteroid Hunter: Identifying asteroid trails in Hubble Space Telescope images, Europlanet Science Congress 2022, Granada, Spain, 18–23 Sep 2022, EPSC2022-1030, https://doi.org/10.5194/epsc2022-1030, 2022.

Introduction
The near-Earth asteroid (NEA) 2021 PH₂₇ was discovered in August 2021. It belongs to the very rare group of Atira objects which stay always within the Earth’s perihelion [1]. Its orbit has a semi-major axis of 0.46 au, an eccentricity of 0.71, and an inclination of 31.9^◦ , with an orbital period of less than 115 days. At perihelion (at 0.13 au) it reaches temperatures above 1000 K and it moves with about 106 km/s with a relativistic perihelion shift of 42.9"/century, 1.6 times that of Mercury. It is therefore an important reference object to understand the interplay between non-gravitational forces, general relativity effects, orbital changes due to the von Zeipel-Lidov-Kozai mechanism [2]. A recent study [3] claims that 2021 PH₂₇ might be an active asteroid which could then produce observable meteor showers on Venus.
The object has an estimated absolute magnitude of 17.8 mag, corresponding to a size range between 0.7 km (high albedo of 0.25) and 2.6 km (radar-based albedo of 0.02 for Atira). Currently, there are 28 Atira (or Apohele) objects known (https://en.wikipedia.org/wiki/Atira_asteroid). Atira objects never cross the Earth’s orbit and there is no impact risk right now. However, they have frequent close encounters with Mercury and Venus which could eventually push an Atira-orbit into an Earth-crossing orbit [2].
The Atira objects represent a part of our Solar System which is poorly known. The few known ones are considered as the ”tip of the iceberg” of a likely numerous population of similar objects which are still undiscovered due to the difficulty to observe so close to the Sun [4]. There are indications that their orbits are the result of gravitational interactions with the Earth-Moon system, Jupiter and Venus [4], but their origin remains an open question [5]. Also, non-gravitational forces, like Yarkovsky and YORP, are expected to play a strong role for long-term orbital evolution [6], for the spin behaviour [7], and possibly also for the shape of these bodies [8].

Observations

In preparation for the challenging VLT-VISIR observations (fast-moving NEA, at high airmass, in twilight), we made astrometric measurements to improve the orbit solution. At the beginning of April 2022, the positional uncertainty reached values below one arcsecond (plane-of-sky 3-σ error).
We observed the thermal emission of 2021 PH₂₇ with VISIR before opposition in April 2022 (leading the Sun), after-opposition measurements (trailing the Sun) are planned for July 2022. In both cases, the object is in a ”half-Moon” configuration (about -90^◦ and +70^◦ phase angle, respectively). Such measurements guarantee that we see once a warm terminator, and once a cold terminator (see Fig. 1). This allows us to determine the asteroid’s sense of rotation, its size and albedo, and to constrain the thermal properties of its surface. This is especially interesting for an asteroid which is frequently heated up to more than 1000 K (e.g. during perihelion in late May 2022 inbetween our VISIR observations). It is expected that the high temperatures have an influence on the surface properties (hence, the thermal inertia) by thermally breaking the solid rock due to very steep temperature gradients between illuminated and shadowed parts of the surface [9].This could also lead to sporadic activity [3].

Fig. 1: Temperature and flux prediction for 2021 PH₂₇ for our thermal observations in early April and mid July 2022. The calculations assume an object albedo of 0.1 (corresponding to a size of about 1.1 km) and a thermal inertia of 500 Jm⁻² K⁻¹s^−0.5.

Our measurements are the first thermal detections of an Atira family member. We also conducted visible lightcurve measurements in Feb, Mar, and Apr 2022, to establish the object’s rotation period and shape properties, and to determine the H-magnitude. The VISIR measurements can be rotationally phased to derive a good-quality size and albedo solution (see e.g., [10,11], and references therein), and to put constraints on its physical shape via well-established thermophysical model techniques [12].

Results

The pair of before/after opposition measurements allows us to determine the objects sense of rotation (prograde or retrograde) [13] which is important to calculate the non-gravitational Yarkovsky force [6], and to look into possible orbital evolution processes which might slowly push this object into the category of potentially hazardous objects [14]. Finding a good model solution for the measurements taken in both VISIR runs also means to constrain the thermal properties of the surface. A high thermal inertia (connected to a rocky or bare-rock surface) will carry substantial heat from the illuminated into the non-illuminated part of the surface (large before/after opposition asymmetry, see Fig. 1). A low thermal inertia (like for our Moon) leads to almost instantaneous thermal equilibrium and would point to a fine-grain regolith with very low conductivity.
The VISIR measurements of 2021 PH₂₇ are the foundation for the characterization of the entire Atira family, for the study of repeated extremely high surface temperatures, and for exploring the largely unknown terrains of poorly detectable NEAs inside the Earth’s orbit. The physical properties of 2021 PH₂₇ are also relevant in the context of disentangling non-gravitational from relativistic orbit effects.

References

1. Ribeiro, A. O., et al. (2016), MNRAS, 458, 4471 – 2. de la Fuente Marcos, C. & R. de la Fuente Marcos (2021), Res. Notes AAS 5, 205 – 3. Carbognani, A, Tanga, P., Bernardi, F. (2022), MNRAS 511, L40-L44 – 4. de la Fuente Marcos, C. & R. de la Fuente Marcos (2019),MNRAS, 487, 2742 – 5. Greenstreet, S., H. Ngo, & B. Gladman (2010), DPS, 42, 13.09 – 6. Bottke, W. F., et al. (2006), AREPS, 34, 157 – 7. Rubincam, D. P. (2000), Icar, 148, 2 – 8. Hirabayashi, M., et al. (2020), Icar, 352, 113946 – 9. Delbo, M., et al. (2014), Natur, 508, 233 – 10. Müller, T., et al. (2017), A&A, 598, A63 – 11. Delbo, M., et al. (2015), aste.book, 107 – 12. Müller, T., et al. (2017),, A&A, 599, A103 – 13. Müller, T. (2002), M&PS, 37, 1919 – 14. La Spina, A., et al. (2004), Natur, 428, 400.

How to cite: Müller, T., Santana-Ros, T., Micheli, M., and Pantin, E.: No one gets closer to the Sun: Thermophysical properties of Atira object 2021 PH27, Europlanet Science Congress 2022, Granada, Spain, 18–23 Sep 2022, EPSC2022-524, https://doi.org/10.5194/epsc2022-524, 2022.

Introduction

The near-Earth asteroid (153201) 2000 WO107 was selected as an M-asteroid candidate based on its known albedo value p_v = 0.129 ± 0.058 [1] and the taxonomic X-type determined from spectral observations [2]. The ambiguous spectral X-type suggests one of the three E-, P-, or M-types, but in this case, given the known albedo, the asteroid is most consistent with an M-type. It has a significantly elongated orbit with e = 0.781, which crosses the orbits of all major inner planets, enters the orbit of Mercury, and approaches the Sun at a distance of q = 0.20 AU. The asteroid has a small size of about 0.5 km and is available for observation only during close approaches to the Earth.

We initiated photometric observations of 2000 WO107 in the 2020 opposition aimed to obtain rotation parameters and estimate its shape and bulk density.

Observations

We carried out photometric observations of (153201) 2000 WO107 in November-December 2020, when the asteroid passed at a minimum distance of 0.029 AU from the Earth. Our observations were made in a coordinated manner at five observatories: the 1-m telescope of the Crimean Astrophysical Observatory, the 70-cm telescope of Abastumani Observatory, the 61-cm telescope of Skalnaté Pleso Observatory, the 36-cm telescope of Kitab Observatory, and the 0.25-m BART telescope of the Roque de los Muchachos Observatory. The observations covered the time interval from Nov. 28 to Dec. 9, 2020, and were done using CCD cameras in R-filter and, moreover, in Kitab without a filter. In addition, the asteroid was also observed in BVI filters on some nights. The measured lightcurves showed a very high amplitude (up to 1.24 mag at the phase angles of 65-70 deg) and made it possible to determine the rotation period of 5.03 hrs (Fig.1). Such a high amplitude characterizes the body of the asteroid as very elongated and possibly binary. Note the unusual flat minima are seen in the light curve. They are a characteristic manifestation of incomplete illumination of an asteroid at large phase angles for synchronous, as well as very elongated bodies of a nonconvex shape. It means that the asteroid is either a binary or a contact binary.

Our assumptions are confirmed by radar observations carried out using the 70-m antenna at the Goldstone Observatory in the same opposition with our observations, which showed that the asteroid is a contact binary with a larger elongated primary component and a smaller secondary close to the sphere [3]. Moreover, the smaller body is attached to the end of the longest axis of the larger body.

Figure 1. The composite light curve obtained from observational data on the night of November 28–29 during the passage of an asteroid at a minimum distance from the Earth.

Modelling

We simulated the scattering of light and radio waves from a bi-lobal asteroid in the assumption of two contacting ellipsoids. The axes of the two ellipsoids, the distance between their centers, the orientation of the rotation axis, the initial rotation phase and the period were used as fitting parameters in a Markov chain Monte Carlo (MCMC) algorithm. The resulted shape model fits well both the optical lightcurves and delay–Doppler images of 2000 WO107 obtained by Goldstone on Nov. 28, 29 and 30, 2020. We estimate the density of 1.5 g/cm³ from the requirement that the resulting shape of the asteroid is mechanically stable.

An independent estimate of the asteroid density can be obtained from its Yarkovsky effect. Greenberg et al. (2020) analyzed measured positions for 2000 WO107 and found the Yarkovsky drift rate to be −24.37 ± 12.7 AU/My [4]. We simulated the Yarkovsky effect of a bi-lobal asteroid using the shape and size of the asteroid obtained from our modelling. Thus, we calculated the theoretical value of the Yarkovsky force acting on this asteroid. By comparing the theoretical Yarkovsky force with the observed Yarkovsky drift rate, we estimated the density of 2000 WO107. Within the error margin, the obtained value agrees with the density determined from the shape modeling.

Conclusions

Combination of photometric and radar data allows us to determine the rotation period and the position of the asteroid's pole, to predict its shape and size, and to measure the asteroid's density.

The resulted density of the near-Earth asteroid (153201) 2000 WO107 is rather low, which implies the asteroid has a predominantly non-metallic composition and most probably belongs to primitive asteroids.

Acknowledgment

Ukrainian team was supported by the National Research Foundation of Ukraine (grant No. 2020.02/0371 “Metallic asteroids: search for parent bodies of iron meteorites, sources of extraterrestrial resources”). The authors are thankful to A. Novichonok and A. Zhornichenko for their help with observations.

References

[1] Mainzer, A., Grav, T., Bauer, J. et al. 2011. Astron. J. 743, Art. 156

[2] Binzel, R. P., Rivkin, A. S., Stuart, J. S., et al. 2004. Icarus 170, 259–294

[3] Benner, L. A. M. Goldstone Radar Observations Planning: (7753) 1988 XB, 2017 WJ16, and 2000 WO107. NASA JPL database “Asteroid Radar Research”. https://echo.jpl.nasa.gov/asteroids/1988XB/1988xb.2020.goldstone.planning.html

[4] Greenberg, A.H., Margot, J.-L., Verma, A.K., Taylor, P.A., Hodge, S.E. 2020. Astron. J. 159, 92

How to cite: Krugly, Y., Mykhailova, S., Golubov, O., Lipatova, V., Inasaridze, R., Ayvazian, V., Kapanadze, G., Datashvili, D., Ehgamberdiev, S., Ivanova, O., Husárik, M., Karpov, S., Slyusarev, I., and Belskaya, I.: Physical characterization of the potentially hazardous contact-binary asteroid (153201) 2000 WO107, Europlanet Science Congress 2022, Granada, Spain, 18–23 Sep 2022, EPSC2022-1150, https://doi.org/10.5194/epsc2022-1150, 2022.

Abstract

The tangential YORP effect (or TYORP) is a radiation pressure torque, which acts on small irregularities of the asteroid surface due to their non-uniform heating. This effect causes asteroids to change their rotation rates, and in many cases, it can be larger than other non-gravitational torques. Other works have already considered TYORP produced by smooth boulders of different shapes on an asteroid's surface. Here, we present the new results on the contribution to TYORP due to the small-scale roughness on the surface of boulders or regolith. We carry out numeric simulations of the 2D heat conduction problem on a sinusoidal surface, average the radiation pressure force in time and space, and thus numerically find the TYORP experienced by the asteroid surface. We also create an approximate analytic theory of heat conduction on a slightly non-flat sinusoidal surface and use it to compute TYORP. We study the small-scale roughness of asteroid Ryugu published in other works and use it to evaluate its TYORP. As a result, we find that the numeric and analytic estimates of the tangential YORP produced by a rough surface are in good qualitative agreement with each other. The contribution of different sinusoidal harmonics to the tangential YORP is additive to good accuracy. It allows us to derive an approximate analytic formula, which expresses TYORP in terms of the Fourier spectrum of the shape of the asteroid surface. The TYORP contribution of the small-scale roughness can be comparable to or even greater than TYORP produced by boulders.

Introduction

The tangential Yarkovsky–O'Keefe–Radzievskii–Paddack effect (also tangential YORP, or TYORP) is caused by the recoil light pressure and drags the asteroid’s surface in the tangential direction [1]. It has previously been simulated for different geometries of smooth boulders [2, 3, 4]. Here, we study the contribution to TYORP arising from the roughness of the asteroid surface on a centimeter-scale, including both non-smoothness of the rocks and the non-flatness of the regolith. We present the recent analytic results from [5] and as yet unpublished results of the numeric simulation of the effect.

Analytic model

We use the perturbation theory to solve the heat conduction equation for a surface whose shape is described by a sinusoidal wave of small amplitude. The resulting temperature is used to compute the light pressure recoil force acting on the surface and thus to evaluate TYORP. 

The expression for TYORP is second-order in terms of the surface slopes, thus it gets vanishingly small if the surface is nearly flat. TYORP of surface roughness has other features previously observed for TYORP of boulders: it vanishes at very small and very big thermal parameters, it vanishes for very short and very long wavelengths of the sinusoidal perturbation of the surface, it is maximal if the thermal parameter is of the order of unity and the wavelength of the sinusoidal perturbation is of the order of the thermal wavelength.

As a qualitative result of this approximate analytic theory, we also obtain that sinusoidal waves with non-commensurable wavelengths do not interfere with each other, and their TYORP is additive. 

Numeric model

We create a computer program that numerically solves the 2D heat conduction equation under the curved surface, and uses the resulting temperature field to compute TYORP. The results of the program qualitatively agree with the analytic model, but differ in exact numeric values due to simplifying assumptions incorporated into the analytic model. We fit the numeric results with an analytic expression and thus get an equation for TYORP as simple as our analytic theory, but more precise than it.

Numeric simulations of TYORP for a surface composed of two sinusoidal harmonics show that different harmonics are almost independent, with the TYORP of a surface being almost equal to the TYORP of individual harmonics.

Results

To apply the theory, we take the high-resolution shape model of asteroid (162173) Ryugu from [6] and decompose its shape into the Fourier harmonics. The additivity of TYORP for different Fourier harmonics tested both analytically and numerically allows us to derive a simple mathematical expression for TYORP as an integral over the Fourier power spectrum of the asteroid surface roughness. Application of this expression to Ryugu results in a TYORP value that is greater than the YORP effect due to the large-scale asymmetry of Ryugu computed from its global shape model [7].

Overall, TYORP produced by the asteroid surface roughness has the same order of magnitude as TYORP produced by boulders. This new component of the YORP effect needs to be computed to correctly predict the dynamics of asteroids, and here we show how this computation can be done.

Acknowledgments

This work was supported by the National Research Foundation of Ukraine, project N2020.02/0371 “Metallic asteroids: search for parent bodies of iron meteorites, sources of extraterrestrial resources”.

References

[1] Golubov O., Krugly Y. N., 2012, ApJL 752, L11
[2] Golubov O., Scheeres D. J., Krugly Y. N., 2014, AJ 794, 22
[3] Sevecek P., Broz M., Capek D., Durech J., 2015, MNRAS 450, 2104
[4] Sevecek P., Golubov O., Scheeres D. J., Krugly Y. N., 2016, A&A 592, A115
[5] Golubov O., Lipatova V., A&A, accepted
[6] Otto K. A., Matz K. D., Schröder S. E., et al., 2021, MNRAS 500, 3178
[7] Kanamaru M., Sasaki S., Morota T., et al., 2021, Journal of Geophysical Research: Planets 126, e2021JE006863.

How to cite: Golubov, O. and Lipatova, V.: A new component of the tangential YORP caused by the roughness of the asteroid surface, Europlanet Science Congress 2022, Granada, Spain, 18–23 Sep 2022, EPSC2022-734, https://doi.org/10.5194/epsc2022-734, 2022.

Introduction

2022 AB is a very small near-Earth asteroid that passed Earth at a distance of 9.6 lunar distances on 20 January.

Our campaign started on 4 January and until 26 January, we observed 2022 AB using telescopes located in many places around the world. More about the campaign, including the determination of the phase curve, will be presented during this conference in a separate presentation [2]. Here we only present results regarding the colour indices, taxonomic class, and diameter. We organised a similar observation campaign for 2021 DW1 in 2021 [3][4][5].
 
Rotation period
 
In determining the colours indices, it is very important to know the rotation period of the asteroid. We discussed the issues, especially in the field of NEAs, at the conference last year [5].
 
We briefly discuss the determination of the rotation period using an example of observations from the first night of the campaign of 2022 AB. More will be discussed in [2].
 
We used a 0.7-m RBT/PST2 telescope(Arizona), 5-s exposures, and the clear filter.  We observed object for 1.5 hours  and we create composite lightcurve with Fourier series fit (see Figure 1). In this way, we determined the rotation period P=182 s.

 

 
Figure 1: Example of composite lightcurve of 2022 AB.
 
Colour indices
 

The preliminary results presented here are based on most of the data obtained. The full results will be presented during the conference.

To determine the colour indices, we used observations from three telescopes: 0.7-m RBT, 1-m telescope of DOAO (South Korea), and 1-m telescope of Pic du Midi Observatory (France). Telescopes from DOAO and Pic du Midi observed the asteroid with an exposure time of several seconds in the B,V,R,I (DOAO) or g’,r’,i’,z’ (Pic du Midi) filters. Due to changes in the geometry of the observations, we divided the observations into several sets. Using solar analogues, we transformed the brightness in B,V,R,I into g’,r’,i’,z’ bands, respectively. Then, knowing the rotation period, we composited the lightcurves to determine the shifts between the lightcurves in the given bands. We have prepared the composited lightcurves separately for each set. An example is shown in Figure 2. RBT observations were made in B,V,R filters and, as we mentioned, transformed them into g’,r’,i’. In this case, we used knowledge of the rotation period to average the brightness measurements over the period, exposure time T_exp=P=182s. Adjacent measurements in different bands allowed us to determine a series of colour indices that we averaged as one set. The results for each set are shown in Table 1.
 
 

 
Figure 2: Composite lightcurves for DOAO set 1. Top: lightcurves in i’ (dots) and z’ band (crosses), middle: i’ and (dots) and r’ (crosses) bands, bottom: r’ (dots) and g’ (cross) bands.
 
 

Table 1: Preliminary results of colour indices for each set.
 
 
Taxonomy
 
To determine the taxonomic class of 2022 AB, we converted the average value of colour indices to the reflection coefficients R_r,R_i and R_z, normalised to the reflection values in the g band, using the formula [6]:
 
R_f=10^{−0.4[(f−g)−(f_☉−g_☉)]}
 
Next, we compared them with spectra of different taxonomic classes, as given by [6]. In Figure 3 we present the reflective value of the asteroid compared to similar taxonomic classes. B class asteroids are rare and they are mainly associated with the outer main belt. 2022 AB as an NEA is an unlikely class B asteroid. The Cb class fits well with the data of 2022 AB and is the only one to show the common with 2022 AB characteristic of visible absorption around 0.6 micrometre. We suggest that 2022 AB is most likely a type Cb asteroid.
 
 

 
Figure 3: Plot of reflectivities values of B,Cb,Ch asteroid classes (black dots) and 2022 AB (red dots). Data for the B,Cb, and Ch classes were taken from [6].

Diameter
 
We can determine the diameter knowing the absolute magnitude H and the albedo p_V according to equation [7]:

D_eff=1329×10^−H/5×p_V^−0.5
 
At the conference, we will present the results based on the determined H from the phase curve, but for now we used the approximate H=23.6±0.36 given by JPL[1]. Albedo for Cb class asteroids: p_V=0.059±0.027 [8], hence D_eff=0.104±0.029 km. 
 
 

 
Figure 4: Rotation period-diameter plot. The red dotted line is the spin barrier (2.2 h). Other asteroid data come from LCDB [8].

 
Acknowledgements
 
This research was funded in whole or in part by the National Science Centre, Poland, grant No. 2021/41/N/ST9/04259.
 
References

[1] https://ssd.jpl.nasa.gov
[2] Kwiatkowski et al. (2022) Photometry and model of near-Earth asteroid 2022 AB from one apparition,EPSC 2022, held 18–23 September 2022 in Granada, Spain
[3] Kwiatkowski et al. (2021) A&A  656, A126
[4] Kwiatkowski et al. (2021) Photometry and model of near-Earth asteroid 2021 DW1 from one apparition, EPSC 2021, held virtually, 13-24 September 2021
[5] Koleńczuk et al. (2021) Determination of colour indices of super-fast rotator near-Earth asteroids, EPSC 2021, held virtually, 13-24 September 2021
[6] DeMeo & Carry (2013), Icarus 226, 723
[7] Fowler and Chillemi (1992) Phillips Laboratory, Hanscom AF Base, MA, 17–43
[8] Warner et al. (2009) Icarus  202, 134

How to cite: Koleńczuk, P., Kwiatkowski, T., Kamińska, M., Kamiński, K., Colas, F., Klotz, A., Kim, T., and Birlan, M.: Colours and taxonomy of 2022 AB: a super fast rotating near-Earth asteroid, Europlanet Science Congress 2022, Granada, Spain, 18–23 Sep 2022, EPSC2022-1161, https://doi.org/10.5194/epsc2022-1161, 2022.

Context

(121) Hermione is a large binary asteroid [1] located at the outer edge of the asteroid belt in the Cybele region, where asteroids are thought to be linked to the outer Solar System. Hermione has a Ch/Cgh-type that has been linked to CM chondrites. Adaptive optics observations between 2003 and 2008 suggest a rare bilobate shape for the primary [2,3]. However, Hermione’s shape and bulk density (ranging between 1.4 and 2 g.cm^-3) remain poorly constrained to this day.

Aim

We acquired spatially resolved images and optical lightcurves of Hermione during its close apparition of September 2021. It was the best chance in 13 years to acquire such high angular resolution images (angular diameter = 0.14”). We aimed to constrain Hermione’s 3D shape, hence its volume, and the orbit of its satellite, hence the mass of the system. Combining the volume and the mass allows to constrain the bulk density with high accuracy.

Methods

We obtained 8 series of 5 images with the SPHERE/ZIMPOL instrument on the Very Large Telescope (ESO Program ID 107.22UT.001; PI: P. Vernazza). These images were combined with optical lightcurves and stellar occultations by the ADAM and MPCD methods [4,5] to reconstruct the asteroid’s 3D shape. For the determination of the satellite’s orbit, we complemented the SPHERE images with a compilation of archival data from other large ground-based AO instruments (KeckII/NIRC2, ESO/VLT/NACO and Gemini-North/NIRI). Then, we used the meta-heuristic algorithm Genoid [6] to accurately determine the orbital elements.

Results

The determined volume and mass of Hermione yield a new higher bulk density of ~1.7 g.cm^-3, more compatible with its Ch/Cgh classification. We will also present our analyse of the shape and compare it with other elongated Ch/Cgh asteroids.

Bibliography

[1] Merline et al. (2002), IAU Circ. 7980

[2] Marchis et al. (2005), Icarus, 178, 2, p. 450-464

[3] Descamps et al. (2009), Icarus, 203, 1, p. 88-101

[4] Viikinkoski, M., Kaasalainen, M., & Durech, J. (2015), A&A, 576, A8

[5] Capanna, C., Gesquière, G., Jorda, L., Lamy, P., & Vibert, D. (2013), The Visual Computer, 29, 825

[6] Vachier, F., Berthier, J. and Marchis, F. (2012), A&1, 543, A68

How to cite: Ferrais, M., Vernazza, P., Marsset, M., Jorda, L., Carry, B., Hanus, J., Brož, M., Yang, B., Fétick, R., Marchis, F., Vachier, F., Birlan, M., Jehin, E., Podlewska-Gaca, E., Bartczak, P., Fusco, T., and Dudziński, G.: Constraining the shape and density of binary asteroid (121) Hermione, Europlanet Science Congress 2022, Granada, Spain, 18–23 Sep 2022, EPSC2022-395, https://doi.org/10.5194/epsc2022-395, 2022.

How to cite: Hanus, J., Vokrouhlicky, D., Nesvorny, D., Durech, J., Stephens, R., Pejcha, O., Benishek, V., and Oey, J.: Shape models and spin states of Jupiter Trojans: Testing the streaming instability formation, Europlanet Science Congress 2022, Granada, Spain, 18–23 Sep 2022, EPSC2022-396, https://doi.org/10.5194/epsc2022-396, 2022.

Phase curves of small bodies are useful tools to estimate sizes and, together with complementary theoretical and laboratory results, to understand their surfaces' micro and macroscopic properties. Although we can observe asteroids up to phase angles of about 30 degrees, the range of phase angles covered by outer solar system objects usually does not go further than 7 to 10 degrees. In this work, we aim to directly compare the phase curves of asteroids observed with low-phase angles with these of outer solar system objects, namely, trans-Neptunian objects and Centaurs.

We used data from the SLOAN Moving objects catalog assuming a simple linear model to compute absolute magnitudes and phase coefficients in the ugriz system, plus V and R filters.

We obtained absolute magnitudes in all filters for more than 4000 objects. Our comparison with outer solar system objects points to the common property of the surfaces: intrinsically redder objects become blue with increasing phase angle, while the opposite happens for intrinsically bluer objects.

How to cite: Alvarez-Candal, A., Jiménez Corral, S., and Colazo, M.: Phase curves at small phase angles of bodies from the SLOAN Moving Objects Catalog, Europlanet Science Congress 2022, Granada, Spain, 18–23 Sep 2022, EPSC2022-128, https://doi.org/10.5194/epsc2022-128, 2022.

How to cite: Colazo, M., Alvarez-Candal, A., and Duffard, R.: Zero-phase angle asteroid taxonomy classification using unsupervised machine learning algorithms, Europlanet Science Congress 2022, Granada, Spain, 18–23 Sep 2022, EPSC2022-660, https://doi.org/10.5194/epsc2022-660, 2022.

How to cite: Robinson, J., Fitzsimmons, A., Young, D., Denneau, L., Smith, K., Bannister, M., Heinze, A., and Tonry, J.: Investigation of Asteroid Phase Curves Extracted from the ATLAS Survey, Europlanet Science Congress 2022, Granada, Spain, 18–23 Sep 2022, EPSC2022-1144, https://doi.org/10.5194/epsc2022-1144, 2022.

Introduction
When talking about Trojan asteroids -- bodies orbiting around the L4 or L5 Lagrangian points of a Sun-planet system -- it is inevitable to refer to Jupiter. This giant planet has, by far, the largest reservoir of Trojan asteroids with thousands of objects discovered since 1906. We currently know, however, that other planets are also able to host asteroids in such a peculiar orbital configuration, although in much smaller number. Trojan asteroids can be important to study the formation and evolution of our Solar System since, some of them – called primordials -- might be remnants of the formation processes of the hosting planet. The first Earth Trojan asteroid (ETA) was discovered in 2010 librating around L4. Thenceforth, several dedicated observational campaigns have been scrutinizing L4 and L5 areas, trying to find a second ETA. In this work we describe how we confirmed (614689) 2020 XL5 as the second ETA and we discuss why it is so arduous to detect these objects with groundbased observations.

Fig.1: The Sun-Earth Lagrangian points. 2020 XL5 is librating around L4. (NOIRLab/NSF/AURA/J. da Silva)

Observations

Asteroid 2020 XL5 was discovered by the Pan-STARRS1 survey on 2020 December 12. An initial orbit determination was obtained from follow-up observations gathered during the next few weeks. Some solutions suggested that 2020 XL5’s orbit could be librating around L4, but the short arc covered with observations was still to short for a long term analysis [8]. However, observations were challenging due to the object’s faintness (V~22 mag) and its proximity with the Sun (ε<40°).

Our team started a follow-up campaign and was able to obtain a few new measurements (Fig.2) of the object during February and March 2021 using ESA’s Optical Ground Station (OGS) 1.0 m telescope, the 4.1 m Southern Astrophysical Research (SOAR) telescope and the 4.3 m Lowell Discovery Telescope (LDT). Despite the successful results of the observation campaign and the consequent improvement of the orbit of 2020 XL5, the arc was still too short for a conclusive result. However, the orbit now allowed us for a detective work among the tons of data from the surveys. Precoveries were found in the files of the Catalina Sky Survey (1.5 m Mt. Lemmon telescope), DECam instrument (4.1 m Victor M. Blanco telescope) and the archive of the 1.8 m Pan-STARRS survey (Fig. 3).

Fig.2: LDT detection of 2020 XL5.

Fig.3: Pan-STARRS ancillary data of 2020 XL5.

Results

Fig.4: a The relative mean longitude (λ_r) evolution of the 2020 XL₅ nominal orbit and clones orbit over 29 000 years, where each clone orbit is represented by a different color, while the green line represents the nominal orbit. b Evolution of λ_r for the nominal orbit of 2020 XL₅. c Stack plot representing the behavior of the nominal orbit and the 800 clone orbits. In the plot the time t₀ = 0 is the mean epoch of the orbits.

With all the data in hand, we generated hundreds of clone orbits along a time span of 29 000 years, applying the Cholesky method for multivariate normal distributions [9]. The study of the relative mean longitude of 2020 XL5 (Fig.4) revealed that the object is indeed a transient ETA, which was captured some 500 years ago and will keep librating around L4 for at least 4000 more years. In addition, we performed a preliminar physical characterization of the asteroid by means of photometry. We estimated its absolute magnitude to be Hr =18.58 (+0.16−0.15), and color indices suggestive of a C-complex taxonomy. Assuming an albedo of 0.06 ± 0.03 we obtained a bulk diameter of 1.18 ± 0.08 km.

References

[1] Dvorak, R. & Schwarz, R. On the stability regions of the Trojan asteroids. Celest. Mech. Dyn. Astron. 92, 19–28 (2005).

[2] Connors, M., Wiegert, P. & Veillet, C. Earth’s Trojan asteroid. Nature 475, 481–483 (2011).

[3] Wiegert, P. A., Innanen, K. A. & Mikkola, S. An asteroidal companion to the Earth. Nature 387, 685–686 (1997).

[4] Whiteley, R. J. & Tholen, D. J. A CCD search for Lagrangian asteroids of the Earth-Sun system. Icarus 136, 154–167 (1998).

[5] Markwardt, L. et al. Search for L5 Earth Trojans with DECam. Mon. Not. R. Astron. Soc. 492, 6105–6119 (2020).

[6] Lifset, N., Golovich, N., Green, E., Armstrong, R. & Yeager, T. A search for L4 Earth Trojan asteroids using a novel track-before-detect multiepoch pipeline. Astron. J. 161, 282 (2021).

[7] Santana-Ros et al. Orbital stability analysis and photometric characterization of the second Earth Trojan asteroid 2020 XL5. Nature Communications 13, 447 (2022)

[8] de la Fuente Marcos, C. & de la Fuente Marcos, R. Transient terrestrial Trojans: comparative short-term dynamical evolution of 2010 TK₇ and 2020 XL₅. Res. Notes Am. Astronomical Soc. 5, 29 (2021).

[9] T., T. N. Essentials of Monte Carlo Simulation (Springer-Verlag, New York, 2013).

Acknowledgements

TSR acknowledges funding from the NEO-MAPP project (H2020-EU-2-1-6/870377). This work was (partially) funded by the Spanish MICIN/AEI/10.13039/ the Institute of Cosmos Sciences University of Barcelona (ICCUB, Unidad de Excelencia ‘María de Maeztu’) through grant CEX2019-000918-M.

How to cite: Santana-Ros, T., Micheli, M., Faggioli, L., Cennamo, R., Devogèle, M., Alvarez-Candal, A., Liu, P.-Y., Benavidez, P. G., and Campo Bagatin, A.: Operating manual on how to find an Earth Trojan asteroid, Europlanet Science Congress 2022, Granada, Spain, 18–23 Sep 2022, EPSC2022-986, https://doi.org/10.5194/epsc2022-986, 2022.

1. Introduction

Linear secular resonances occur when there is a commensurability between the frequency of precession of an asteroid perihelion, g, or node, s, and that of a planet. The ν₆ involves a relationship between the frequency g of an asteroid and the g6 frequency of Saturn. Since it is a pericenter resonance, it can increase most asteroids’ eccentricities to planet-crossing levels. It can, therefore, destabilize most of the bodies that interact with it, and it is a major source of NEAs through Yarkovsky effect [2]. Despite this fact, stable orbital configurations exist inside the ν₆ resonance. In such configurations, the resonant angle σ = ϖ  −ϖ₆, with ϖ  the longitude of pericenter of the asteroid and ϖ₆ that of Saturn, can oscillate around either 0◦ or 180◦. In the first case, we have an “aligned libration”, since the pericenters of both Saturn and the asteroid are pointing in the same direction. For the second case, we have an “anti-aligned libration”.

[4] identified the first case of an asteroid family completely made of asteroids in anti-aligned libration states, that of 1222 Tina. [6] extended this analysis to the whole main-belt, and found the first seven asteroids in aligned states of the same resonance. Here, we extended the previous analysis using the largest database of asteroid proper yet obtained.

2. Identification of the resonant population using large databases

To identify the population of ν₆ resonators, first, we need to select the asteroids most likely to be affected by this resonance. For this purpose, we use the criterion described in [6] and the approach outlined in [3].  We identified 15 asteroids on aligned orbital configurations, and 1713 on anti-aligned ones (see figure (1)). We then proceeded searching for asteroid groups among the newly identified anti-aligned population using the Hierarchical Clustering Method (HCM) [1]. Our results are shown in figures (2). We identify a new group around the asteroid 12988 Tiffanykapler.

3. 12988 Tiffanykapler: the first young family in the ν₆ secular resonance

Young asteroid families can be dated using methods based on numerical integrations of family members in the past, like the Backward Integration Method (BIM, [7]) and the Close Encounters Method (CEM, [5]). In the BIM method, from time-reversal numerical simulations, past discrepancies in the longitudes of node Ω of family members with regard to those of the claimed parent body are obtained. These differences should converge to values approaching zero at the time of family formation. The CEM approach works by integrating into the past multiple clones of the parent body and of the other family members. Close encounters that occur at low relative distances and speeds between two clones are recorded, and the median value of these times is used to estimate the asteroid pair’s age.  The results of both methods are shown in figure (3). The BIM method suggests a possible solution for the 12988 group in the time range from 3.3 to 6.5 Myr. The weighted average of the age determination of all asteroid pairs in the family, one example of which is shown in the right panel of figure (3), provides an age estimate for the family of 3.05 ± 1.15 Myr.

As discussed in [4], at the simplest level of perturbation theory the quantity:

is preserved for asteroids in the ν₆ resonance in the conservative case. The preservation of the original values of K₂' permits to estimate the initial ejection velocity field with a method not generally available for non-resonant families. Our analysis yields a value of the ejection velocity parameter V_EJ = 15⁺⁶_-3 m/s.

4. Summary and Conclusions

In this work, we were able to obtain a sample of 15 asteroids on aligned orbits and 1669 asteroids on anti-aligned orbits, the largest database so far for this asteroidal population. Two new asteroid groups were identified for the first time in this work: those of Tiffanykapler in the inner main-belt and 138605 QW177 in the outer belt. Tiffanykapler is the first young asteroid family in a linear resonant configuration ever to be found. Combining methods based on backward numerical simulations and constraints from resonant dynamics, we found that the family has an age of 3.05 ± 1.15 Myr and an ejection velocity field parameter of V_EJ = 15⁺⁶_-3 m/s. Finally, using resonant proper elements ([4]), we also identified a highly eccentric population of asteroids near the Tina family, that are likely to be part of its halo. It is the first example of a “resonant halo”.

Acknowledgements

We thank the Brazilian National Research Council (CNPq, grant 301577/2017-0), and the Foundation for Research Support of São Paulo state
(FAPESP, grant 2016/024561-0). More information on this work is available on Carruba et al. 2022, MNRAS, under review, available on ArXiv: 2203.15763.

References

[1] BENDJOYA, P., AND ZAPPALÀ, V. Asteroid Family Identification. In Asteroids III. Arizona Univ. Press, 2002, pp. 613–618.

[2] BOTTKE, W. F., JEDICKE, R., MORBIDELLI, A., PETIT, J.-M., AND GLADMAN, B. Understanding the Distribution of Near-Earth Asteroids. Science 288, 5474 (June 2000), 2190–2194.

[3] CARRUBA, V., A LJBAAE, S., DOMINGOS, R. C., AND BARLETTA, W. Artificial neural network classification of asteroids in the M1:2 mean-motion resonance with Mars. MNRAS 504, 1 (June 2021), 692–700.

[4] CARRUBA, V., AND MORBIDELLI, A. On the first ν₆ anti-aligned librating asteroid family of Tina. MNRAS 412, 3 (Apr. 2011), 2040–2051.

[5] CARRUBA, V., S POTO, F., BARLETTA, W., ALJBAAE, S., FAZENDA, Á. L., AND MARTINS, B. The population of rotational fission clusters inside asteroid collisional families. Nature Astronomy 4 (Jan. 2020), 83–88.

[6] HUAMAN, M., ROIG, F., CARRUBA, V., DOMINGOS, R. C., AND ALJBAAE, S. The resonant population of asteroids in librating states of the ν₆ linear secular resonance. MNRAS 481, 2 (Dec. 2018), 1707–1717.

[7] NESVORNÝ, D., BOTTKE, WILLIAM F., J., DONES, L., AND L EVISON, H. F. The recent  breakup of an asteroid in the main-belt region. Nature 417, 6890 (June 2002), 720–771.

How to cite: Carruba, V., Aljbaae, S., Domingos, R. C., Huaman, M., and Martins, B.: Identifying the population of stable ν6 resonant asteroids using large databases, Europlanet Science Congress 2022, Granada, Spain, 18–23 Sep 2022, EPSC2022-238, https://doi.org/10.5194/epsc2022-238, 2022.

Abstract

The aim of this work is to investigate the dynamics of small bodies that are in co-orbital motion with a given planet in the solar system. The study is based on the data corresponding to the ephemerides computed by the JPL Horizons system for asteroids with a low inclination with respect to the Sun-planet orbital plane. These objects are cataloged according to their dynamics as seen in the averaged formulation of the Restricted Three-Body Problem in the circular-planar case. The tool developed can show where asteroids in horseshoe motion, quasi-satellite motion and tadpole motion are located, together with the dynamical transitions that occur in the given timeframe. The results will provide the first catalog of asteroids in co-orbital motion in the solar system at the moment and an efficient mean to study dynamical transitions. Moreover, for the Earth case, possible targets for future retrieval and exploration mission can be pinpointed.

Introduction

Co-orbital motion is a particular type of dynamics that occurs in the Three-Body Problem, according to which two bodies gravitate towards a more massive body with the same period. 
Many objects susceptible to be at least temporary co-orbitals have been observed in the solar system, in particular for Venus, Earth, Mars and Jupiter.
A major example is given by the Trojans of Jupiter, that move on tadpole (TP) trajectories in the neighborhood of the two Lagrange's equilateral configurations L₄ and L₅ in the synodic reference system. In the prograde case, the other two fundamental configurations are horseshoe (HS) trajectories and quasi-satellite (QS) orbits.

Co-orbital trajectories, their possible mutual transitions together with escaping/trapping mechanisms are not only evident in the natural dynamics observed in the solar system, but very recently they have also assumed an important role for space exploration missions. For instance, ESA is  planning to exploit L₅ of the Sun-Earth system to monitor the solar activity and the related space weather issues. The Chinese space agency aims at visiting the near-Earth asteroid Kamo'oalewa, due to its interesting QS state.

The idea of this work comes from the development of Pousse and coauthors [1,2], regarding the averaged Hamiltonian of the Restricted Three-Body Problem (RTBP) in the circular-planar case. From the theoretical point of view the domain of validity of the analytical model has been proved, here we are interested in testing its validity against real bodies dynamics and to propose some applications. The main tool we will consider is a simple map, that is function of the orbital eccentricity of the heliocentric motion of the asteroid and the relative phase between the planet and the asteroid, and that can comprise all the important information about the motion of the asteroid.

Methods

Taking as example a system composed by the Sun, a planet and an asteroid, we assume the RTBP approximation in the circular-planar case. Following the co-orbital assumption, the asteroid orbits the Sun with the same orbital period as the planet orbits the Sun. The resonant condition on the orbital periods allows for very stable solutions, that are indeed observed in the solar system, as mentioned above.

We are interested in depicting the dynamics of the asteroid with regard to the orbital elements associated with its heliocentric motion. In particular, since the motion is assumed to be planar, we will focus on its semi-major axis a and eccentricity e and an angle θ, related to the relative phase with respect to the motion of the planet. 
Since we focus on the co-orbital dynamics, that can be seen as the continuation of Keplerian orbits in 1:1 mean motion resonance with the planet, the most natural choice appears to tackle the problem by means of a perturbative treatment, considering the mass parameter of the system as the perturbative parameter. By adopting a suitable set of resonant variables and the possibility to separate different timescales, the dynamics can be described by a 1 degree-of-freedom integrable model, that allows to depict simple phase space portraits that catch the main secular features.

The instruments corresponding to the averaged perturbation theory are applied to the ephemerides computed by the JPL Horizons system over about 900 years for asteroids that can be in co-orbital motion with Venus, Earth, Jupiter or Saturn, with an inclination low enough to be considered almost coplanar with the given planet. The analysis aims at identifying the asteroids in 1:1 mean motion resonance at the current time, not only in TP motion, and to reveal the possible mechanisms of transitions (see an example in Fig. 1) between co-orbital configurations and not. In particular, we analyse the transitions with respect to the limits of our model (e.g., non-negligible inclination, or external effect).

Figure 1: Example of transition between horseshoe motion and quasi-satellite motion.

A simple map, function of (θ,e), is used to characterize the given Sun-planet system. The asteroids that are in co-orbital motion with Jupiter at an epoch corresponding to the actual one within a certain threshold are shown in Fig. 2.

Figure 2: General map to represent the co-orbital asteroids for a given Sun-planet system. Here we show the results obtained for Jupiter in the almost co-planar case.

Acknowledgments
The authors are indebted with Federica Spoto from CFA Harvard and with Tommaso Del Viscio from IMATI-CNR. A.P and E.M.A. acknowledge the support received by the project entitled "co-orbital motion and three-body regimes in the solar system", funded by Fondazione Cariplo through the program "Promozione dell'attrattività e competitività dei ricercatori su strumenti dell'European Research Council - Sottomisura rafforzamento".

References

[1] Pousse A., Robutel P., Vienne A., On the co-orbital motion in the planar restricted three-body problem: the quasi-satellite motion revisited. Celest. Mech. Dyn. Astron. 128(4), 383-407 (2017)

[2] Pousse A., Alessi E.M., Revisiting the averaged problem in the case of mean-motion resonances in the restricted three-body problem. Nonlinear Dynamics 108, pages 959-985 (2022)

How to cite: Alessi, E. M., Pousse, A., and Di Ruzza, S.: Averaged theory applied to the co-orbital motion of real asteroids in the solar system in the medium-term timescale, Europlanet Science Congress 2022, Granada, Spain, 18–23 Sep 2022, EPSC2022-119, https://doi.org/10.5194/epsc2022-119, 2022.

The NEO population model derived by Granvik et al. (2016,2017,2018) suggested that there is an overestimate of objects in low perihelion distance (q) orbits when compared to the observed population. The remedy to this discrepancy was to include a super-catastrophic disruption of objects when they crossed an average disruption distance, defined as q*=0.076 au. The mechanism responsible for destroying such objects is not determined yet, but it is believed to be thermal in nature.

How to cite: Toliou, A. and Granvik, M.: The recent dynamical past of the low perihelion NEO population, Europlanet Science Congress 2022, Granada, Spain, 18–23 Sep 2022, EPSC2022-1014, https://doi.org/10.5194/epsc2022-1014, 2022.

There are a large number of small bodies (known as trans-Neptunian objects or TNOs) in the outer solar system that show different types of dynamical behavior. These objects can be considered as "probes" of the dynamical and chemical history of the Solar System. These asteroids or planetezimals are relics of dynamical events among and beyond the giant planets, and the current observed orbital distribution of the TNOs is a sign of large-scale changes in the position of the giant planets. The dynamical classification of the bodies of this outer region of the Solar System helps to understand the structure and formation of the Solar System. In this work, we performed a comprehensive survey on the TNOs. By using the FAIR method considering all known small bodies in outer Solar System (more than 4,000 asteroids classified as TNO in the JPL database), we identified several MMRs between these bodies and the planet Neptune. According to our dynamical investigations, there are two types of resonant behaviour of asteroids; namely, when the critical argument (resonance variable) shows short-term or long-term libration.

How to cite: Forgács-Dajka, E., Kővári, E., Kovács, T., Kiss, C., and Sándor, Z.: Dynamical Investigation of Trans-Neptunian Objects in particular the Mean-Motion Resonances with Neptune, Europlanet Science Congress 2022, Granada, Spain, 18–23 Sep 2022, EPSC2022-1213, https://doi.org/10.5194/epsc2022-1213, 2022.

In a recent research, we carried out a large-scale survey of the trans-Neptunian objects (TNOs) by means of dynamical maps. We identified the most important MMRs and explored their dynamical role through the quantification of the chaotic diffusion and that of the stability times of the small bodies. The chaotic diffusion is of fundamental importance for its rate determines the long-term evolution of a given celestial system. To estimate the rate of the diffusion (that is, to compute the diffusion coefficients) in the case of more than 4100 TNOs, we initiated the use of the Shannon entropy. This latter quantity allows, on the one hand, to measure the extent of unstable regions in the phase space (and thus serves as an indicator of chaos), and also enables the direct measurement of the diffusion coefficients. The characteristic times of stability - in the case of normal diffusion - are then achieved by taking the inverse of the diffusion coefficients. In the knowledge of the chaotic diffusion and stability times for as large a TNO sample as the one indicated above, the overall structure of the trans-Neptunian space can be mapped, along with the specification of dynamical classes or the update of the existing ones.

How to cite: Kővári, E., Forgács-Dajka, E., Kovács, T., Kiss, C., and Sándor, Z.: Chaotic behaviours of different time-scales in the trans-Neptunian space, Europlanet Science Congress 2022, Granada, Spain, 18–23 Sep 2022, EPSC2022-1216, https://doi.org/10.5194/epsc2022-1216, 2022.

Introduction:  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]. In 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:  G-mode method leads to an automatic statistical clustering of a sample containing N objects (NEOs in this case), described by M variables with the only control imposed by the user being the confidence level q1, expressed in terms of σ. The objects that cannot be associated to a cluster are separated and considered as outliers. We apply G-mode multivariate statistical clustering analysis to variables defining  NEOs to determine clustering of objects.

Our sample consists of 14132 NEOs, filtered based on their orbital uncertainty. Our input parameters to the G-mode method are twofold. First, in approach 1 (A1) we used three variables and their uncertainties as inputs:  inclination (i), eccentricity (e) and semi-major axis (a) of the orbit. In approach 2 (A2) we used six inputs by including the argument of perihelion (ω), Tisserand parameter with respect to Jupiter (TJ) and the absolute magnitude (H) and their respective uncertainties in addition to those used in A1.

Results:  In A1, we obtained only one cluster at  q1=3σ (accurate classification probability of 99.7%), which meant that the NEOs in this cluster are homogeneous in terms of the three orbital elements used. As we gradually lowered the value of q1, hence the confidence level, we noticed that more clusters got seeded and populated. We report in Table 1, mean parameter values with the median absolute deviation for 8 clusters obtained at q1=1.78σ. In addition to reporting the statistics of obtained clusters, we have also reported the outlier group of NEOs in the row indexed by 0. Among the reported clusters, cluster 1 (C1) corresponds to the background population of NEOs as their statistics are comparable to those of all hitherto discovered NEOs. C2 represents NEOs with relatively moderate inclination. C3, despite having relatively small number of NEOs, is constrained by well-behaved low-inclined, quasi-circular Earth-like orbits owing to their very low median absolute deviations. The very low mean H implies that these NEOs are relatively smaller with a distribution peak in the range of 5-15 meters of diameter.

C5, C6 and C7 are of particular interest, for they could be associated with Jupiter-family cometary nuclei (2 < TJ < 3) as per their mean TJ. As such, the objects in these three clusters could potentially be extinct cometary nuclei. These clusters also have relatively higher eccentricities, akin to cometary orbits. We have checked available taxonomic classifications of NEOs [11,12,13] in the literature to get an insight into the composition of the objects. Although taxonomic classifications are not available for the majority of members in the clusters, we find that (i) C5 contains 3 C-types, 2 D-types and 0 S-types (ii) C6 contains 3 D-types and 4 S-types (iii) C7 contains 2 B-types, 3 C-types, 2 D-types and 1 S-type. Therefore we argue that C5 and C7 can be associated to primitive carbonaceous compositions while C6 can be associated to both carbonaceous and silicate-dominated compositions.

To get more insights about the obtained G-mode clusters and further test these results, we applied a dynamic model to find their potential escape regions in the main belt [14]. This dynamical model, the Granvik model hereafter, traces with scrutiny the escape paths of objects from the main-belt to near-Earth space and the model accounts for the Yarkovsky effect [15]. Given the orbital elements and absolute magnitude of an NEO, it resolves a probability distribution function, built up of seven discrete values for seven escape regions. The results obtained with the Granvik model are shown in Fig. 1 for the clusters obtained for the G-mode run at q1=1.78σ in A1.

Fig. 1. Probability distributions for the G-mode clusters obtained at 1.78σ for A1 to emanate from any of the seven escape regions.

These results imply that most of the clusters have higher probability to emanate via ν₆ secular resonance, known to be the most dominant escape path from the main-belt to the near-Earth space [16]. We observe that C5 and C7 have significant probabilities to emanate from outer-belt sources such as 2:1 mean motion resonance of Jupiter and JFCs. Thus, our dynamic modelling reinforces and corroborates existing results, pointing towards a primitive origin for the NEOs in these two clusters.

Similiary, we will present the results of A2 and discuss their implications.

Acknowledgements: We acknowledge the financial support from Agenzia Spaziale Italiana (ASI, contract No. 2017-37-H.0 CUP F82F17000630005) and 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. 347,6220,1261952

[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,AJ130,1291

[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

[14] Granvik, M., Morbidelli, A., Jedicke, R., et al. 2018,Icarus,312,181

[15] Vokrouhlický, D., Bottke, W. F., Chesley, S.R., Scheeres, D.J., & Statler, T.S. 2015, in Asteroids IV,509–531

[16] Bottke, W.F., Morbidelli,A., Jedicke,R., et al. 2002,Icarus,156,399

How to cite: Deshapriya, J. D. P., Perna, D., Bott, N., Hasselmann, P. H., Granvik, M., Dotto, E., Fulchignoni, M., Giunta, A., Perozzi, E., Ieva, S., Petropoulou, V., and Mazzotta-Epifani, E.: Statistical clustering analysis of NEOs to find correlations with spectral classes, Europlanet Science Congress 2022, Granada, Spain, 18–23 Sep 2022, EPSC2022-698, https://doi.org/10.5194/epsc2022-698, 2022.

Finding a link between meteorites and asteroids thanks to spectroscopy gives a great insight of the composition of the bodies in the asteroid population. Meteorites such as the Howardite-Ensatites-Diogenites (HEDs) have been successfully linked to the asteroid Vesta (McCord et al. (1970), summary by McSween Jr. et al. (2013)), and the ordinary chondrite meteorite population has been connected to a subtype of S-type asteroids, after having taken into account space weathering processes (Binzel et al. 2001). These processes alter the surface of asteroids and modify their reflectance spectra with respect to that of the fresher meteorites, hence they need to be taken into account prior to comparing asteroids with meteorites spectra (Hapke 2001). Other meteorite types have been studied and linked to asteroid types, but some objects still do not show convincing connections (DeMeo et al. 2022). Linking meteorites to the primordial population of objects would give information about the formation and evolution of bodies in the Solar System. Indeed, the planetesimals that formed earliest in the Solar System are thought to have been fully differentiated, due to the melting induced by the heating produced by the radioactive decay of 26Al isotopes. This should have resulted in planetesimals presenting a basaltic crust, an olivine-dominated mantle and an iron-rich core (DeMeo et al. 2019). However most of these primitive objects have evolved, have been disrupted or integrated to other bodies (such as planets) and their formation processes and the composition of their primordial crusts is not well known.

We will report about searching for potential parents bodies of meteorites coming from differentiated planetesimals, using literature data and the new dataset of reflectance spectra that will be released in the Gaia Data Release 3 (DR3) in June 2022. This dataset will present low resolution mean reflectance spectrum of 60 518 Solar System objects, acquired by Gaia’s blue and red spectrophotometers (BP and RP) between August 2014 and May 2017. Each spectrum will consist of 16 discrete wavelength bands that spans the visible wavelength range from 374 to 1034 nm (Gaia collaboration, Galluccio, Delbo et al. 2022). These data should allow to look inside asteroid collisional families and search for hints of differentiation, looking for members corresponding to the crust, mantle or core of a disrupted planetesimal. We intend to use these data to try to link meteorites that are known to have been produced by differentiation (e.g. metallic or andesitic bodies) to the primordial population of asteroids. Finding the parent body of differentiated meteorites would allow to understand better the formation and differentiation of planetesimals in our Solar System.

To compare the reflectance spectra of meteorites with Gaia’s asteroids, we will first use a curve matching method. Curve matching consists in determining whether any given spectrum is similar to a reference spectrum, by the means of a coefficient that has to be minimized (such as the χ2) or maximized (correlation coefficient for example) (Popescu et al. 2012). We will as well study the features of the spectra in order to better characterize the asteroids and validate the matches (Gaffey 2011). Space weathering processes will be taken into account.

Acknowledgements
The authors acknowledge the financial support of CNES and OCA, which make this study possible. M. Delbo thanks financial support from the ANR ORIGINS (ANR-18-CE31-13-0014).

References
Binzel, R. P., Rivkin, A. S., Bus, S. J., Sunshine, J. M., & Burbine, T. H. 2001, Meteoritics & Planetary Science, 36, 36
DeMeo, F. E., Burt, B. J., Marsset, M., et al. 2022, Icarus, 380, 114971
DeMeo, F. E., Polishook, D., Carry, B., et al. 2019, Icarus, 322, 13
Gaffey, M. J. 2011, AIP Conference Proceedings, 1386, 1386
Gaia collaboration, Galluccio, Delbo et al. 2022 Gaia Data Release 3: Reflectance spectra of Solar System Small Bodies. A&A under review.
Hapke, B. 2001, J. Geophys. Res., 106, 10039
McCord, T. B., Adams, J. B., & Johnson, T. V. 1970, Science, 168, 1445
McSween Jr., H. Y., Binzel, R. P., De Sanctis, M. C., et al. 2013, Meteoritics & Planetary Science, 48, 48
Popescu, M., Birlan, M., & Nedelcu, D. M. 2012, A&A, 544, 544

How to cite: Galinier, M., Delbo, M., Galluccio, L., and Marrocchi, Y.: Searching for parent bodies of differentiated meteorites in the main-belt using visible and near-infrared spectroscopy, Europlanet Science Congress 2022, Granada, Spain, 18–23 Sep 2022, EPSC2022-351, https://doi.org/10.5194/epsc2022-351, 2022.

Asteroids, along with other small bodies, are what is left over of the original planetesimal disk from the planet-formation era. Therefore, these objects are considered the best tracers for the processes that occurred during the earliest history of our Solar System. However, the majority of asteroids are fragments generated by the collisional breakup of the planetesimals, the first ~100-km sized bodies (Morbidelli et al., 2008, Delbo' et al., 2019) that accreted in the protoplanetary disk of our Sun.

Nevertheless, a small fraction of the planetesimal population survived the collisional evolution. In order to study these objects, the first step is to identify these surviving planetesimals among all the other (fragment) asteroids. To do so, we “cleaned” the inner part of the asteroid main belt (2,1 < a < 2,5) from all asteroid collisional family members (using the method of Bolin et al., 2017, Delbo' et al., 2017, 2019), thus revealing those asteroids that are not fragments that formed in the main belt. Thanks to this method, we revealed 64 surviving planetesimals in the inner main belt.

We carried out a spectroscopic survey of these identified IMB planetesimals, in order to constrain their composition and mineralogy. In particular, we performed visible and near-infrared spectroscopy using several telescopes such as the 1.82m Copernico Telescopio (Asiago, Italy) for the visible spectroscopy and the 4.2 Lowell Discovery Telescope (Flagstaff, USA); the 3.2 NASA Infrared Telescope Facility (Hawaii, USA) and the Telescopio Nazionale Galileo (La Palma, Spain) for the near-infrared part. To complete our survey, we also used spectra in the visible and near-infrared published in the literature, as well as size and albedo information that we obtained from the Minor Planet Physical Properties Catalog (https://mp3c.oca.eu/).

We performed the taxonomic classification following the Bus-DeMeo taxonomy (Bus et al., 2002; DeMeo et al., 2009), and using the M4AST tool (http://m4ast.imcce.fr) (Popescu et al., 2012). A visual inspection to identify the presence of absorption bands characteristic of some classes was performed to check the robustness of the automatic taxonomic classification. In addition, we compute for each planetesimal several spectral parameters, such as spectral slopes, and center, depth and area of absorption bands, when these are present. We also performed calculation of their mass, based on the method of (Carry, 2012). Finally, we used the RELAB database (Pieters, 1983), to look for meteorite analogues of each planetesimal.

We found that planetesimals of the Inner Main Belt (IMB) belong mainly to the S-complex (~45%), followed by C-complex (~25%) and X-complex (~17%). Further investigations on S-complex planetesimals showed that, for a majority of them, they are best matched by spectra of ordinary chondrites meteorites. We did not find any correlation with diameters, semimajor axis and the ratio of olivine/pyroxene. Almost 60% of the C-complex planetesimals belong to the Ch/Cgh types, showing spectroscopic features associated with hydrated minerals, and consequently indicating the presence of liquid water in the early formation phases of these objects. We also found that almost 5% of the IMB planetesimals belong to the D/T types with a diameter greater than 25 km. As this taxonomical class, as well as Ch/Cgh types, are likely to have formed in the outer part of the Solar System (at 3-7 au), their presence in the IMB (2,1-2,5 au) can be explained by dynamical models invoking large semimajor axis migration of these objects (e.g., Grand Tack of Walsh et al., 2011; low-mass asteroid belt of Raymond and Izidoro, 2017b for the C-complex and Vokrouhlický et al., 2016 for the D/T types).

Here, we will present the spectroscopic, physical and compositional results of our IMB planetesimals survey as well as the implications for planetary formation models.

Acknowledgements: We acknowledge support from the ANR ORIGINS (ANR-18-CE31-13-0014).

References : Morbidelli A. et al, Physica Scripta, Volume 130, Issue, id 014028 (2008) ; Delbo M. et al., A&A, Volume 624, id. A69 (2019) ; Bolin B. T. et al., Icarus, Volume 282, 2017, Pages 290-312 ; Delbo M. et al., Science, Volume 357, Issue 6355, pages 1026-1029, (2017) ; Bus S. J. et al., Icarus, Volume 158, Issue 1, Pages 146-177 (2002) ; DeMeo F. E. et al., Icarus, Volume 202, Issue 1, Pages 160-180 (2009); Carry, B. Planetary and Space Science, Volume 73, Issue 1, p. 98-118. (2012) ; Popescu M. et al., A&A, Volume 544, id. A130 (2012) ; Pieters, C. M., J. Geophys. Res., Volume 88, pages 9534– 9544 (1983) ; Walsh K. J. et al., Nature, Volume 475, Issue 7355, Pages 206-209 (2011) ; Raymond S. N. et al., Science Advances, Volume 3, Issue 9, Pages e1701138 (2017) ; Vokrouhlický D. et al., The Astronomical Journal, Volume 152, Issue 2, id. 39 (2016).

How to cite: Bourdelle de Micas, J., Fornasier, S., Delbo, M., Avdellidou, C., Van Belle, G., and Ochner, P.: Composition of Inner Main Belt Planetesimals, Europlanet Science Congress 2022, Granada, Spain, 18–23 Sep 2022, EPSC2022-440, https://doi.org/10.5194/epsc2022-440, 2022.

Introduction:  V-type asteroids are those whose spectra is similar to Vesta [1].

Vesta underwent two huge impact events [2], that could have formed objects of this taxonomic class [3,4] and have eventually supplied the Vesta meteorites (HEDs) escaped from the Main Belt.

In this work, we look for statistically significant differences among the modal mineralogy of V-type asteroids belonging to different dynamical subclasses through a combination of spectroscopic analysis and Hapke Radiative Transfer Model (RTM).

Data and Methods:  76 Vis-NIR V-type asteroid spectra were downloaded from the Planetary Data System (PDS). In this work, we considered four dynamical families of V-type as follows:

(i) Vestoid: V-type members of the Vesta dynamical family, as defined by [4] using the hierarchical clustering method (HCM).

(ii) Fugitive: following the definition of [4], they are V-type asteroids with a < 2.3 au and comparable e and i with the Vesta family.

(iii) Low-I: according to [4], they are V-type asteroids having i < 6◦ and 2.3 < a < 2.5 au.

(iv) IOs (Inner Others): the remaining V-type asteroids in the inner main belt.

VNIR spectra of Vesta’s, V-type asteroids surface and HED show absorption bands centred at approximately 0.9 and 1.9μm, confirming the pyroxenes presence [5]. Through scatterplot analysis of spectral parameters (in particular, band depth and half width half maximum) of V-type asteroids and of HED, these two bands give evidence of the grain size range of each asteroid. The obtained information is used as constrain in the Hapke’s RTM  (to prevent possible degeneration in the creation of synthetic spectra) to retrieve modal composition for each V-type asteroid. To simulate asteroids spectra in the Hapke RTM, we used the main endmembers of HED and we also added a darkening agent (Murchison spectrum) to find possible correlations between V-type asteroids and dark regions on Vesta [6].

Spectral fits of the asteroid’s dataset are robust with a global R mean square of 0.98, while the retrieved particle sizes are small with a mean value of 20 µm.

Results and Discussion: Comparing the modal mineralogy obtained from Hapke RTM and the [7] studies, it is possible to assign a lithology to each dynamical subclass. In particular, we can distinguish diogenites (approximately 100 % of pyroxene), noritic diogenites (2-42 % plagioclase, 52-97 pyroxene), cumulate eucrite (30-64 % plagioclase and 36-70 % pyroxene) and basaltic eucrite (39-46% plagioclase, 46-60 % pyroxene).

Then, in Figure 1, we report the mean and the standard deviation of sample of the four subclasses (Fugitive, Vestoids, Inner Others and Low-i). It seems that Vestoids and Fugitive are diogenitic (diogenitic and noritic diogenites respectively), while Low-I and Inner Other (IOs) are eucritic (Figure 2).

Figure 1: Results of mean mineralogy for each subclass from Hapke retrival

Figure 2: Probability density function of Pyroxene (up) and of Plagioclase (bottom) for each subclass

The most ‘ancient’ family, that is Low-i asteroids (they may date back to the LHB epoch or even to the 4.48-Ga impact on Vesta), seems to have an eucritic composition. In the most recent models of the structure of Vesta, it has a massive eucritic crust. Moreover, [2] found that the density of craters increases from the Rheasilvia rim to northern latitudes. This dichotomy in terms of crater density indicates that heavily cratered terrains (centered at about 348°E, 17°N and 110°E, 17°N) are much older than Rheasilvia basin, whose most probable age is estimated to be 1.0 ± 0.2 Ga [2]. Thus, it is compatible with the mineralogy of the Low-I asteroids that ‘swept out’, in the past, the outermost layer of Vesta.

Fugitive better match with a diogenitic composition. For this subclass, the probable age of formation is at least 1 Ga so that they could migrate away from Vesta [4], then it is possible that they were ejected in an older (2 Ga) cratering event that produced the Veneneia basin that underlies Rheasilvia [8].

Furthermore, [9] found from Dawn data that Rheasilvia basin (probable age is estimated to be 1.0 ± 0.2 Ga [9]) is consistent with a larger abundance of diogenite on the surface, while spectra from the equatorial regions are consistent with a larger eucrite amount. Thus, there is a possible chronologic link between impact events on Rheasilvia crater and the Vestoids, which, from our work, have a mineralogy associated to Diogenites.

In any family, there is no signature of dark material as carbonaceous chondrites (here we used Murchison spectra to simulate it). This could be explained by the fact that it has an exogenous origin [6,10], and it could have impacted on Vesta after the V-type family formation.

From this work, a possible chronologic link between impact events on Vesta and the V-type family is possible. We plan to augment the database of V-type asteroids to improve the statistical analysis.

References: [1] De Meo,F. E. et al. (2009), Icarus, n. 202,p.160–180; [2] Marchi, S. et al. (2012), SCIENCE, Vol 336, Issue 6082, pp. 690-694; [3] Carruba, V. et al. (2007), A&A 465, 315-330;[4] Nesvorny, D. et al. (2008), Icarus, vol 183, 85–95;  [5] De Sanctis,M.C. et al. (2013), Meteorit. Planet. Sci, vol. 48, n. 11, p. 2166–2184; [6] Palomba,E et al. (2014), Ica-rus, n. 240, pp. 58-72;  [7] Mittlefehldt,D.W. et al. (2015), Chemie der Erde, vol. 75, pp. 155-183 ; [8] McSween, H.Y.J. et al. (2013), Meteorit. Planet. Sci, vol. 48, n. 11, p. 2090–2104; [9] De Sanctis, M.C. et al. (2012), SCIENCE ,VOL 336; [10] Turrini, D. et al. (2014), Icarus, 240, 86-102

How to cite: Angrisani, M., Palomba, E., Longobardo, A., Raponi, A., Gisellu, C., and Dirri, F.: Are there significant differences among the mineralogy of V-type asteroids family?, Europlanet Science Congress 2022, Granada, Spain, 18–23 Sep 2022, EPSC2022-270, https://doi.org/10.5194/epsc2022-270, 2022.

Introduction:  The 4 Vesta asteroid is a differentiated asteroid, i.e. it has experienced melting and its structure is distinct layered: crust, mantle, nucleus. Hence, study of materials from different depths of Vesta would be helpful to understand its evolutionary history. Moreover, Vesta preserves information on the composition of primordial smaller asteroids that impacted on its surface. Vesta bright surface shows indeed dark units [1], that are supposed to be linked to exogenous material, and are therefore useful to understand the initial stages of the Solar System.

The VIR spectrometer on board the NASA’s Dawn spacecraft [2], that orbited Vesta for approximately one year, collected thousands of hyperspectral images of its surface. Vesta spectra show the 2.7-2.8 μm absorption band, due to the presence of the OH molecule, whose distribution is inversely correlated with the reflectance of its surface [3]. In fact, it is included in carbonaceous chondrites, that are the darkening agents of the Vesta’s dark units [4].

Scientific Objectives:  In this work we took advantage of the newly calibrated data of the VIR spectrometer, which are characterized by a better signal to noise (S/N) ratio, giving us the opportunity to search for spectral features that were never seen before, due to noise. Basing on this, the goals of this work were to: 1) confirm, reinforce and characterize the OH distribution on Vesta by studying the 2.7-2.8 µm band and by looking for OH combination bands that occur around 2.2-2.4 µm; 2) search for and characterize possible carbonates, that are supposed to be included in carbonaceous chondrites, i.e., the darkening agents of Vesta; 3) characterize the Vesta surface in the visible range.

OH absorption band: The analysis on absorption bands related to the hydroxyl evidenced an anticorrelation between the abundance of hydroxyl and the reflectance of the surface (Figure 1). This confirms that the OH molecule is linked to the presence of the dark units on Vesta [3]. This is also a definitive proof that dark hydrated impactors (likely carbonaceous chondrites) are the darkening agents on Vesta, ruling out other interpretations suggested in literature (regolith grain size, impact shock and presence of opaque-rich eucrites and metals) [1].

Figure 1: Anti-correlation between the 2.8 µm band depth and the reflectance of the surface.

We searched for the presence of possible combination bands centered around 2.2-2.4 µm. Weak features at 2.4 µm were found but no correlation with the 2.8 µm absorption band has been proved, so we can say that this feature is not related to the OH molecule and is likely a spectral artifact (Figure 2).

Figure 2: This scatterplot shows that the 2.4 µm feature is not correlated to the 2.8 µm absorption band.

Search for carbonates:  We were not able to identify the 3.9 µm and the 3.4 µm absorption bands related to the presence of carbonates. This does not necessarily mean that carbonates are absent, but their abundance is not sufficient to observe an absorption band emerging from spectral noise. We compared VIR spectra with synthetic spectra of Vesta analogous mixtures (developed by applying a radiative transfer model) to calculate the upper limit of the abundance of carbonates on Vesta. The results show that carbonaceous chondrites that impacted on Vesta, contain no more than 0.5-2% of carbonates, in agreement with petrochemical analyses of typical Carbonaceous chondrites [5].

Caracterization in the visible range: The visible spectra showed an absorption band around 0.5 µm in addition to the strongest well known pyroxenes absorption band centered at 0.9 µm. We made a scatterplot between the 0.5 µm band depth and the 1.9 µm band depth related to the pyroxenes (Figure 3). In the scatterplot a linear dependance between the two features is evident. This proves that the 0.5 µm absorption band is due to the presence of the pyroxenes. Other features found in the visible range were instead associated to spectral artifacts. This emphasizes the results found by [6].

Figure 3: Correlation between the absorption band at 0.5 µm and the absorption band of the pyroxenes at 1.9 µm.

References:

[1] Palomba E. et al. (2014) Icarus, 240, 58–72.

[2] De Sanctis M. C. et al. (2011) SSR, 163, 329.

[3] De Sanctis M. C. et al. (2012) The astrophysical Journal Letters., 758.2, p. L36.

[4] McCord T. B. et al. (2012) Nature, 491.7422 , 83-86.

[5] de Leuw S., Rubin A. E., Wasson, J. T. (2010) Meteoritics & Planetary Science, 45.4, 513-530.

[6] Rousseau B. e al. (2021) Astronomy and Astrophysics, 653.

How to cite: Massa, G., Longobardo, A., Palomba, E., Angrisani, M., Gisellu, C., Dirri, F., De Sanctis, M. C., Raponi, A., Carrozzo, G., and Ciarniello, M.: Vesta surface composition as derived from newly calibrated Dawn data., Europlanet Science Congress 2022, Granada, Spain, 18–23 Sep 2022, EPSC2022-554, https://doi.org/10.5194/epsc2022-554, 2022.

The classification of the minor planets of the Solar System has been revisited regularly since its first outline in the 1970s as dichotomy of carbonaceous and silicaceous asteroids. The reformulations followed insights granted by new data (e.g. surveys such as ECAS, SMASS) or extensions of the observable feature space (e.g. CCD spectroscopy).

Since the last major update of the taxonomy by DeMeo et al. in 2009, we have seen a wealth of new data provided by targeted campaigns, which show that the spectroscopically-defined class boundaries do not align sufficiently with mineralogical and meteoritic population trends. Examples are the continuous trend between B- and C-type objects (Clark et al. 2010, De Leon et al. 2012) and the large subclassing of the continuous S-type asteroids (Vernazza et al. 2014). Furthermore, any compositional interpretation of members of the X-complex is tentative as shown by the diversity of radar albedos, densities, and spectral properties observed among them (Shepard et al. 2010, 2015, Carry 2012, Neeley et al. 2014).

Given the increase of data and insights into the compositional asteroid Main Belt, we derive a new iteration of the asteroid taxonomy, focusing primarily on a methodological improvement. Acknowledging that future survey efforts will contribute asteroid spectra in different wavelength ranges (e.g. Gaia (visible), SPHEREx (NIR), MITHNEOS (visible-NIR)), we evolve the current method into a probabilistic model approach which enables us to classify complete and partially observed spectra in the same scheme. We further re-introduce the visual albedo into the classification space to disentangle the degenerate X-complex.

By means of a clustering analysis of almost 3,000 minor body spectra and albedos, we devise a taxonomic scheme consisting of 17 classes with close resemblance to the Bus-DeMeo and Tholen systems (refer to Fig. 1): A, B, C, Ch, D, E, K, L, M, O, P, Q, R, S, X, V, Z. The two main complexes remain C and S. We resolve the X-complex and replace it by the new M-complex. Subclasses in the Bus-DeMeo system are replaced by a mineralogical interpretation of the continuous distribution of minor bodies in the classification space. The new class Z entails extremely-red objects in the inner Main Belt including the supposed TNO-implants (203) Pompeja and (269) Justitia (Hasegawa et al. 2021).

A python-tool to classify minor body observations in the derived taxonomic scheme is freely accessible to the community (https://classy.readthedocs.io).

Figure 1: Evolution of the asteroid taxonomy from the Tholen- (Tholen 1984) over the Bus-DeMeo- (Bus and Binzel 2002, DeMeo et al. 2009) to the system established in this work.

References

Clark, B. E., Ziffer, J., et al. (2010), Spectroscopy of B-type asteroids: Subgroups and meteorite analogs.
Carry, B. (2012), Density of asteroids.
Bus, S. J. and Binzel, R. P. (2002), Phase II of the Small Main-Belt Asteroid Spectroscopic Survey. A Feature-Based Taxonomy.
DeMeo, F. E., Binzel, R. P., et al. (2009), An extension of the Bus asteroid taxonomy into the near-infrared.
de León, J., Pinilla-Alonso, N., et al. (2012), Near-infrared spectroscopic survey of B-type asteroids: Compositional analysis.
Hasegawa, S., Marsset, M., et al. (2021), Discovery of Two TNO-like Bodies in the Asteroid Belt.
Neeley, JR., Clark, BE., et al. (2014), The composition of M-type asteroids II: Synthesis of spectroscopic and radar observations.
Shepard, M. K., Clark, B. E., et al. (2010), A radar survey of M- and X-class asteroids II. Summary and synthesis.
Shepard, M. K., Taylor, P. A., et al. (2015), A radar survey of M- and X-class asteroids. III. Insights into their composition, hydration state, & structure.
Vernazza, P., Zanda, B., et al. (2014), Multiple and Fast: The Accretion of Ordinary Chondrite Parent Bodies.

How to cite: Mahlke, M., Carry, B., and Mattei, P.-A.: A New Iteration of the Asteroid Taxonomy, Europlanet Science Congress 2022, Granada, Spain, 18–23 Sep 2022, EPSC2022-385, https://doi.org/10.5194/epsc2022-385, 2022.

Abstract

The Gaia mission of the European Space Agency (ESA) published its third release (DR3) on June 13, 2022, including for the first time a survey of 60 518 mean reflectance spectra of Solar System objects (SSOs). Each reflectance spectrum was derived from calibrated measurements obtained by the onboard Blue and Red low-resolution spectro-photometers (BP/RP) and consists of sixteen discrete wavelength bands, along with additional information about the data quality for each band.

We will describe the processing of the Gaia spectral data of SSOs and the steps of our internal validation procedures. We present the adopted approach for external validation against SSO reflectance spectra available in the literature, obtained from ground-based and space-borne telescopes, to assess the quality of Gaia SSO reflectance spectra. This work summarizes a more detailed description by Galluccio et al. (2022) [1].

• Introduction

Gaia DR3 contains information for a sample of more than 150,000 SSOs, including astrometry, photometry, osculating elements, and mean reflectance spectra [2]. The selection of these objects is described by Tanga et al. (2022) [2]. Based on the quality of the data and some criteria developed hereafter, DR3 contains 60518 mean reflectance spectra of Near-Earth Asteroids (NEAs), main-belt asteroids, Jupiter Trojans, transneptunian objects (TNOs), and other classes (Table 1) observed at relatively large phase angles (~20°).

Table 1: No. of SSOs with Gaia DR3 spectra for each of the dynamical classes listed on the NASA JPL website. The classes are defined according to the criteria based on the orbital semi-major axis a, the perihelion distance q, and the aphelion distance Q.

• Production of SSO reflectance spectra

The first step in computing the SSO mean reflectance spectra consisted of a calibration of the BP/RP spectra and removal of all instrumental and astrophysical effects to produce internally calibrated epoch spectra [3]. Each of them is an array of 60 internal flux measurements and corresponding uncertainties, computed for each one of the 60 pixel-long XP (BP/RP). The BP operates in the wavelength range λ between 330 and 680 nm, and RP between 640 and 1050 nm. Next, BP and RP epoch reflectance R(λi)_t were determined by dividing the flux f_t(λi) of each SSO spectrum at the epoch t by the reference solar analogue spectrum F(λ). The latter has been computed by averaging Gaia DR3 mean spectra of several known solar analogue stars widely used in asteroid ground-based spectroscopy because their spectra closely mimic the one of our Sun. Epoch reflectance was then normalized at λ = 550 nm. To compute the mean reflectance spectrum, we first defined a set of fixed wavelength bands, each one having a width of 44 nm, in the interval from 374 nm to 1034 nm. Inside each wavelength band, we computed a weighted average reflectance using all epoch reflectance present in each bin after applying a sigma-clipping procedure (see Figure 1).

Figure 1: Example of the mean computed reflectance R(λi) (black circles) for the asteroid (61) Danae. The grey points are the R(λi)_t corresponding to each epoch reflectance. The R(λi) _t values accepted by our filtering method are coloured in blue (BP) and red (RP).

Some filters based on SNR and on quality criteria were finally applied to the sample of computed mean reflectance spectra. Along with the mean reflectance spectra, the Gaia DR3 catalogue also contains for each source a reflectance_spectrum_flag field, indicating the overall quality of the resulting reflectance spectrum.

• Validation

The validation of the Gaia DR3 mean reflectance spectra was obtained by studying and comparing spectral parameters including the spectral slope and the absorption band depth around 900 nm (equivalent to SDSS z-i colour) with those available in the literature, including the SMASSII survey [4] (Figure 2), ground-based observations at large phase angle [5] or space-borne telescope spectra. In general, Gaia DR3 mean reflectance spectra are in good agreement with the literature data. No significant spectral reddening was detected during the validation step.

Figure 2: z colour vs. spectral slope of the asteroids of DR3 (grey dots). Over-plotted with circles of different colours are the same spectral parameters computed by us (see Section 4.2) for the asteroids of SMASSII [4]. The letters C, S, and X represent taxonomic complexes, the other letters spectral classes

• Conclusions

Gaia DR3 includes the largest space-based survey of reflectance spectra of Solar System small bodies observed at visible wavelengths with excellent quality. In the presentation of Delbo et al. (2022) at this conference some preliminary results about the Gaia view of asteroid collisional families will be described.

Acknowledgements

This work has made use of data from the European Space Agency (ESA) mission Gaia (https://www.cosmos.esa.int/gaia), processed by the Gaia Data Processing and Analysis Consortium (DPAC, https://www.cosmos.esa.int/web/gaia/dpac/consortium). Funding for the DPAC has been provided by national institutions, in particular the institutions participating in the Gaia Multilateral Agreement.

References

[1] Gaia collaboration, Galluccio, Delbo et al. 2022 Gaia Data Release 3: Reflectance spectra of Solar System Small Bodies. A&A under review.   
[2] Gaia collaboration, Tanga et al. 2022 Gaia Data Release 3: the Solar System survey. A&A under review.
[3] De Angeli et al. 2022, Gaia Data Release 3: Processing and validation of BP/RP low-resolution spectral data A&A under review.
[4] Bus and Binzel. 2002. Icarus 158, 146-177.
[5] Cellino, Bendjoya, Delbo’ et al. 2020. A&A, 642, A80

How to cite: Galluccio, L., Delbo, M., De Angeli, F., Pauwells, T., Tanga, P., Mignard, F., Cellino, A., Brown, A. G. A., Muinonen, K., and Penttilä, A.: Survey of Solar system small bodies reflectance spectra in Gaia Data Release 3, Europlanet Science Congress 2022, Granada, Spain, 18–23 Sep 2022, EPSC2022-357, https://doi.org/10.5194/epsc2022-357, 2022.

The Gaia mission of the European Space Agency (ESA) was launched in December 2013 and began it scientific operations in July 2014. Gaia is essentially devoted to the measurement  of positions, parallaxes, proper motions, brightnesses, and colours of stars. However, Gaia has also obtained astrometric, photometric, and spectroscopic measurements for several hundreds of thousands of asteroids. 

The Gaia Data Release 3 (DR3) is the first to contain low resolution reflectance spectra of 60,518 solar system small bodies, the large majority of which are asteroids of the main belt (Gaia collaboration, Galluccio, Delbo et al. 2022). The global survey properties, the methods of data production and validation are detailed in the aforementioned paper published by the journal Astronomy and Astrophysics, which accompanies the DR3, and also summarised in the presentation of Galluccio et al. (2022) at this conference (EPSC 2022). 

Here we present preliminary results about the Gaia view of asteroid collisional families. We identified asteroids belonging to families during the validation of Gaia asteroid spectra. Based on the family identification of Nesvorny et al. (2015), with the addition of the New Polana and the Eulalia families from Walsh et al. (2013), we found that in the Gaia DR3 there are 25,088 asteroids that belong to 116 collisional asteroid families of the 121 listed in Tab.1. This table also reports the number of family members and the number of members with a Gaia DR3 reflectance spectrum. However, the family identification of current catalogues is conservative by construction in order to keep good separation between the families. Hence, it is very likely that (i) some of the known families are more extended than what is available in current catalogues, namely, that catalogues based on dynamical criteria do not capture the whole extent of a family, and (ii) some unknown families are yet to be identified. This implies that the aforementioned number of asteroid family members with Gaia DR3 reflectance spectra is likely an estimation lower than the true number. 

We will present some important features that Gaia observed in families. One of these is the correlation between some spectral parameters, such as the slope and the depth of the 1-micron absorption band of the reflectance spectrum, and the age of members of asteroid families belonging to the so called spectroscopic S-complex (DeMeo et al. 2009). These correlations can be explained in terms of a space weathering process that reddens and reduces the 1-band depth as a function of time on S-complex asteroids.

For the brightest asteroids, the extension of Gaia reflectance spectra at wavelengths shorter than 0.45 micron is very useful for distinguishing the composition of primitive, carbonaceous asteroid families, which are difficult to be discriminated with the ground based spectroscopic data currently present in the literature. 

References:

- DeMeo, F. E., Binzel, R. P., Slivan, S.~M., Bus, S. J. 2009. Icarus 202, 160–180.

- Gaia collaboration, Galluccio, Delbo et al. 2022. A&A under review. 

- Nesvorný, D., Brož, M., & Carruba, V. 2015.  in Asteroids IV (P. Michel, et al. eds.) University of Arizona Press, Tucson.,

- Walsh, K. J., Delbo, M., et al. 2013. Icarus 225, 283–297. 

How to cite: Delbo, M., Galluccio, L., De Angeli, F., Pauwels, T., Tanga, P., Miagnard, F., Cellino, A., Brown, A., Muinonen, K., and Penttila, A.: Gaia spectroscopic view of asteroid collisional families: preliminary results, Europlanet Science Congress 2022, Granada, Spain, 18–23 Sep 2022, EPSC2022-237, https://doi.org/10.5194/epsc2022-237, 2022.

Long-awaited, Gaia Data Release 3 was published 2022, on June 13th and contains ultra-precise astrometric measurements for over 150 000 small bodies in the Solar System (Tanga et al. 2022). Compared to Gaia DR2, this release will contain a longer observational arc which is crucial in finding subtle non-gravitational forces, such as the Yarkovsky effect (A2 or da/dt). The main consequence of this perturbation is a secular drift of the semi-major axis (a) of small bodies.

The influence of Gaia data in the determination of the Yarkovsky effect has already been proven (Gaia Collaboration, Spoto et al. 2018, Spoto et al. 2019, Dziadura et al. 2022, Tanga et al. 2022). This effect is now quite well known for Near-Earth Asteroids but still remains hard to detect especially for objects in the Main Belt. 

So far we have tried to detect the Yarkovsky effect for all NEAs, Mars Crossers and MBA objects available in Gaia DR2 (606 objects). We used the new weighting scheme (Spoto et al., in preparation) which contains weights for observations depending on: the observatory code, the stellar catalogue used for reduction, the epoch of the observations, and a given magnitude class. We present our result in Fig. 1. The S value represents S = A2(this work)/A2(expected) where the expected value is determined as in Spoto et al. (2015). There are 13 asteroids which meet the conditions of S > 2 and SNR > 3 (green points), all of them are NEAs. In Fig. 2 and 3 we plotted the same asteroids in dependency of diameter (d) and semimajor axis respectively. As expected we conclude that even with Gaia DR2, this effect still remained difficult to detect for Mars Crossers and MBAs. 

We present preliminary results obtained from Gaia DR3. We selected all the objects with a diameter < 5 km and we compared our detected value to the expected value determined based on the physical and orbital parameters of the objects.

Acknowledgements

This work presents results from the European Space Agency (ESA) space mission Gaia. Gaia data are being processed by the Gaia Data Processing and Analysis Consortium (DPAC). Funding for the DPAC is provided by national institutions, in particular the institutions participating in the Gaia MultiLateral Agreement (MLA). The Gaia mission website is https://www.cosmos.esa.int/gaia. The Gaia archive website is https://archives.esac.esa.int/gaia.

The research leading to these results has received funding from the Ministry of Science and Higher Education of Poland in the years 2018/2022, as a research project under the ‘‘Diamond Grant’’ program, grant number 0062/DIA/2018/47.

References

Tanga et al. 2022, Gaia Data Release 3: the Solar System Survey, 2022, submitted to A&A

Gaia Collaboration, Spoto et al. 2018: Gaia Data Release 2: Observations of Solar System Objects, 2018, A&A

Spoto, F., Tanga, P., & Carry, B. (2019, September). Direct detections of the Yarkovsky drift with Gaia DR2. In EPSC-DPS Joint Meeting (p. 182)

Dziadura, K., Oszkiewicz, D., & Bartczak, P. (2022). Investigating the most promising Yarkovsky candidates using Gaia DR2 astrometry. Icarus, 115040

Spoto, F., Milani, A., & Knežević, Z. (2015). Asteroid family ages. Icarus, 257, 275-289

Del Vigna, A., Faggioli, L., Milani, A., Spoto, F., Farnocchia, D., & Carry, B. (2018). Detecting the Yarkovsky effect among near-Earth asteroids from astrometric data. Astronomy & Astrophysics, 617, A61

Figure 1. S parameter as a function of signal to noise ratio SNRA2. Green circles represent accepted values (SNRA2 > 3 and S < 2) - consistent with expected value determined, blue circles are marginal cases (2.5 < SNRA2 < 3 and S < 2), and red are values with SNRA2 > 3 or S > 2.5. Horizontal line represents S = 2. The Vertical line represents SNRA2 = 3. (Del Vigna et al. 2018)

Figure 2. The Color bar represents the dependence of the asteroid's diameter. If the diameter was not available in JPL it was calculated from the absolute magnitude. Axes as in Figure 1.

Figure 3. The Color bar represents the dependence of the asteroid's semimajor axis. Axes as in Figure 1.

How to cite: Dziadura, K., Spoto, F., Oszkiewicz, D., Carry, B., Bartczak, P., and Tanga, P.: Computing the Yarkovsky effect for asteroids in Gaia DR3, Europlanet Science Congress 2022, Granada, Spain, 18–23 Sep 2022, EPSC2022-649, https://doi.org/10.5194/epsc2022-649, 2022.