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Trojan asteroids are small bodies orbiting around the L 4 or L 5 Lagrangian points of a Sun-planet system. Due to their peculiar orbits, they provide key constraints to the Solar System evolution models. Despite numerous dedicated observational efforts in the last decade, asteroid 2010 TK 7 has been the only known Earth Trojan thus far. Here we confirm that the recently discovered 2020 XL 5 is the second transient Earth Trojan known. To study its orbit, we used archival data from 2012 to 2019 and observed the object in 2021 from three ground-based observatories. Our study of its orbital stability shows that 2020 XL 5 will remain in L 4 for at least 4 000 years. With a photometric analysis we estimate its absolute magnitude to be H r = 18.5 8 − 0.15 + 0.16 , and color indices suggestive of a C-complex taxonomy. Assuming an albedo of 0.06 ± 0.03, we obtain a diameter of 1.18 ± 0.08 km, larger than the first known Earth Trojan asteroid. Although Trojan asteroids have been known for decades in other Solar System planets, only one Earth Trojan asteroid was detected. Here, the authors show that recently discovered 2020 XL 5 is the second transient Earth Trojan asteroid.

Understanding the physical characteristics of small Solar System bodies is important not only for refining formation and evolution models but also for space mission operations. Although several kilometre-sized asteroids have been visited by spacecraft, asteroid 1998 KY 26 —the final target of Hayabusa2#, the extended mission of the Japan Aerospace Exploration Agency’s Hayabusa2 spacecraft—will be the first decametre-scale asteroid to be explored in situ. Its small size and rapid spin place it above the upper limit on the rotation rate, indicating it may differ from previously studied bodies. In this work, we conducted a photometric campaign during 1998 KY 26 ’s close approach to Earth in 2024, revealing a high optical albedo and Xe-type colours. We determine its spin period to be (5.3516 ± 0.0001) minutes—half the period of earlier estimates. Lightcurve inversion produces retrograde pole solutions in both convex and non-convex shape models. Combined with 1998 Goldstone radar data, these results give a diameter of (11 ± 2) m, three times smaller than previously derived values. The derived cohesive strength levels necessary to keep the structure intact, which is less than 20 Pa, suggest a possibility of the asteroid’s rubble pile structure, though this finding does not rule out its monolithic structure. These results can be validated with future James Webb Space Telescope observations. Our comprehensive characterisation can inform the planning of the Hayabusa2# rendezvous in 2031 and helps pave the way for future studies of dark comets. Asteroid 1998 KY26 is the target of Hayabusa2 extended space mission. Here, authors show that it is smaller and rotates faster than known.

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

Trojan asteroids are small bodies orbiting around the L or L Lagrangian points of a Sun-planet system. Due to their peculiar orbits, they provide key constraints to the Solar System evolution models. Despite numerous dedicated observational efforts in the last decade, asteroid 2010 TK has been the only known Earth Trojan thus far. Here we confirm that the recently discovered 2020 XL is the second transient Earth Trojan known. To study its orbit, we used archival data from 2012 to 2019 and observed the object in 2021 from three ground-based observatories. Our study of its orbital stability shows that 2020 XL will remain in L for at least 4 000 years. With a photometric analysis we estimate its absolute magnitude to be [Formula: see text], and color indices suggestive of a C-complex taxonomy. Assuming an albedo of 0.06 ± 0.03, we obtain a diameter of 1.18 ± 0.08 km, larger than the first known Earth Trojan asteroid.

Asteroid spectroscopy reflects surface mineralogy. There are few thousand asteroids whose surfaces have been observed spectrally. Determining the surface properties of those objects is important for many practical and scientific applications, such as for example developing impact deflection strategies or studying history and evolution of the Solar System and planet formation. The aim of this study is to develop a pre-selection method that can be utilized in searching for asteroids of any taxonomic complex. The method could then be utilized im multiple applications such as searching for the missing V-types or looking for primitive asteroids. We used the Bayes Naive Classifier combined with observations obtained in the course of the Sloan Digital Sky Survey and the Wide-field Infrared Survey Explorer surveys as well as a database of asteroid phase curves for asteroids with known taxonomic type. Using the new classification method we have selected a number of possible V-type candidates. Some of the candidates were than spectrally observed at the Nordic Optical Telescope and South African Large Telescope. We have developed and tested the new pre-selection method. We found three asteroids in the mid/outer Main Belt that are likely of differentiated type. Near-Infrared are still required to confirm this discovery. Similarly to other studies we found that V-type candidates cluster around the Vesta family and are rare in the mid/oter Main Belt. The new method shows that even largely explored large databases combined together could still be further exploited in for example solving the missing dunite problem.

By analyzing brightness variation with ecliptic longitude and using the Lowell Observatory photometric database, we estimate spin-axis longitudes for more than 350 000 asteroids. Hitherto, spin-axis longitude estimates have been made for fewer than 200 asteroids. We investigate longitude distributions in different dynamical groups and asteroid families. We show that asteroid spin-axis longitudes are not isotropically distributed as previously considered. We find that the spin-axis longitude distribution for main-belt asteroids is clearly non-random, with an excess of longitudes from the interval 30{\\deg}-110{\\deg} and a paucity between 120{\\deg}-180{\\deg}. The explanation of the non-isotropic distribution is unknown at this point. Further studies have to be conducted to determine if the shape of the distribution can be explained by observational bias, selection effects, a real physical process or other mechanism.

Infrared measurements of asteroids are crucial for the determination of physical and thermal properties of individual objects, and for the understanding of the small-body populations in the solar system as a whole. But standard radiometric methods can only be applied if the orbit of an object is known, hence its position at the time of the observation. We present MIRI observations of the outer-belt asteroid 10920 and an unknown object, detected in all 9 MIRI bands in close proximity to 10920. We developed a new method \"STM-ORBIT\" to interpret the multi-band measurements without knowing the object's true location. The method leads to a confirmation of radiometric size-albedo solution for 10920 and puts constraints on the asteroid's location and orbit in agreement with its true orbit. Groundbased lightcurve observations of 10920, combined with Gaia data, indicate a very elongated object (a/b >= 1.5), with a spin-pole at (l, b) = (178{\\deg}, 81{\\deg}), and a rotation period of 4.861191 h. A thermophysical study leads to a size of 14.5 - 16.5 km, a geometric albedo between 0.05 and 0.10, and a thermal inertia in the range 9 to 35 Jm-2s-0.5K-1. For the newly discovered MIRI object, the STM-ORBIT method revealed a size of 100-230 m. The new asteroid must be on a very low-inclination orbit and it was located in the inner main-belt region during JWST observations. A beaming parameter {\\eta} larger than 1.0 would push the size even below 100 meter, a main-belt regime which escaped IR detections so far. These kind of MIRI observations can therefore contribute to formation and evolution studies via classical size-frequency studies which are currently limited to objects larger than about one kilometer in size. We estimate that MIRI frames with pointings close to the ecliptic and only short integration times of a few seconds will always include a few asteroids, most of them will be unknown objects.

We explore the correlation between an asteroid's taxonomy and photometric phase curve using the H, G12 photometric phase function, with the shape of the phase function described by the single parameter G12. We explore the usability of G12 in taxonomic classification for individual objects, asteroid families, and dynamical groups. We conclude that the mean values of G12 for the considered taxonomic complexes are statistically different, and also discuss the overall shape of the G12 distribution for each taxonomic complex. Based on the values of G12 for about half a million asteroids, we compute the probabilities of C, S, and X complex membership for each asteroid. For an individual asteroid, these probabilities are rather evenly distributed over all of the complexes, thus preventing meaningful classification. We then present and discuss the G12 distributions for asteroid families, and predict the taxonomic complex preponderance for asteroid families given the distribution of G12 in each family. For certain asteroid families, the probabilistic prediction of taxonomic complex preponderance can clearly be made. The Nysa-Polana family shows two distinct regions in the proper element space with different G12 values dominating in each region. We conclude that the G12-based probabilistic distribution of taxonomic complexes through the main belt agrees with the general view of C complex asteroid proportion increasing towards the outer belt. We conclude that the G12 photometric parameter cannot be used in determining taxonomic complex for individual asteroids, but it can be utilized in the statistical treatment of asteroid families and different regions of the main asteroid belt.

The amount of sparse asteroid photometry being gathered by both space- and ground-based surveys is growing exponentially. This large volume of data poses a computational challenge owing to both the large amount of information to be processed and the new methods needed to combine data from different sources (e.g. obtained by different techniques, in different bands, and having different random and systematic errors). The main goal of this work is to develop an algorithm capable of merging sparse and dense data sets, both relative and differential, in preparation for asteroid observations originating from, for example, Gaia, TESS, ATLAS, LSST, K2, VISTA, and many other sources. We present a novel method to obtain asteroid phase curves by combining sparse photometry and differential ground-based photometry. In the traditional approach, the latter cannot be used for phase curves. Merging those two data types allows for the extraction of phase-curve information for a growing number of objects. Our method is validated for 26 sample asteroids observed by the Gaia mission.

As evidenced by recent survey results, majority of asteroids are slow rotators (P>12 h), but lack spin and shape models due to selection bias. This bias is skewing our overall understanding of the spins, shapes, and sizes of asteroids, as well as of their other properties. Also, diameter determinations for large (>60km) and medium-sized asteroids (between 30 and 60 km) often vary by over 30% for multiple reasons. Our long-term project is focused on a few tens of slow rotators with periods of up to 60 hours. We aim to obtain their full light curves and reconstruct their spins and shapes. We also precisely scale the models, typically with an accuracy of a few percent. We used wide sets of dense light curves for spin and shape reconstructions via light-curve inversion. Precisely scaling them with thermal data was not possible here because of poor infrared data: large bodies are too bright for WISE mission. Therefore, we recently launched a campaign among stellar occultation observers, to scale these models and to verify the shape solutions, often allowing us to break the mirror pole ambiguity. The presented scheme resulted in shape models for 16 slow rotators, most of them for the first time. Fitting them to stellar occultations resolved previous inconsistencies in size determinations. For around half of the targets, this fitting also allowed us to identify a clearly preferred pole solution, thus removing the ambiguity inherent to light-curve inversion. We also address the influence of the uncertainty of the shape models on the derived diameters. Overall, our project has already provided reliable models for around 50 slow rotators. Such well-determined and scaled asteroid shapes will, e.g. constitute a solid basis for density determinations when coupled with mass information. Spin and shape models continue to fill the gaps caused by various biases.