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1. The Astronomical Journal The American Astronomical Society logo. The Institute of Physics logo. A publishing partnership The following article is Open access Photometric Confirmation and Characterization of the Ennomos Collisional Family in the Jupiter Trojans

   Wong, Ian; Brown, Michael E (December 2023, Astronomical Journal)

   The Astronomical Journal The American Astronomical Society logo. The Institute of Physics logo. A publishing partnership The following article is Open access Photometric Confirmation and Characterization of the Ennomos Collisional Family in the Jupiter Trojans Ian Wong3,1 and Michael E. Brown2 Published 2022 December 16 • © 2022. The Author(s). Published by the American Astronomical Society. The Astronomical Journal, Volume 165, Number 1 Citation Ian Wong and Michael E. Brown 2023 AJ 165 15 DOI 10.3847/1538-3881/ac9eb3 Download Article PDF DownloadArticle ePub Download PDF Download ePub Article metrics 474 Total downloads 4 4 total citations on Dimensions. Share this article Abstract Collisional families offer a unique window into the interior composition of asteroid populations. Previous dynamical studies of the Jupiter Trojans have uncovered a handful of potential collisional families, two of which have been subsequently confirmed through spectral characterization. In this paper, we present new multiband photometric observations of the proposed Ennomos family and derive precise g − i colors of 75 candidate family members. While the majority of the targets have visible colors that are indistinguishable from background objects, we identify 13 objects with closely grouped dynamical properties that have significantly bluer colors. We determine that the true Ennomos collisional family is tightly confined to and , and the majority of its confirmed members have near-solar spectral slopes, including some of the bluest objects hitherto discovered in the Trojan population. The property of distinctly neutral colors that is shared by both the Ennomos family and the previously characterized Eurybates family indicates that the spectral properties of freshly exposed surfaces in the Jupiter region are markedly different than the surfaces of uncollided Trojans. This implies that the processes of ice sublimation and space weathering at 5.2 au yield a distinct regolith chemistry from the primordial environment within which the Trojans were initially accreted. It also suggests that the Trojans were emplaced in their present-day location from elsewhere sometime after the initial population formed, which is a key prediction of recent dynamical instability models of solar system evolution. 

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2. Photometric Properties of Jupiter Trojans Detected by the Dark Energy Survey

   https://doi.org/10.3847/PSJ/aca4d1  

   Pan 潘, Jiaming 嘉明; Lin 林, Hsing Wen; Gerdes, David W.; Napier, Kevin J.; Wang 王, Jichi 骥驰; Abbott, T. M.; Aguena, M.; Allam, S.; Alves, O.; Bacon, D.; et al (December 2022, The Planetary Science Journal)

   Abstract The Jupiter Trojans are a large group of asteroids that are coorbiting with Jupiter near its L4 and L5 Lagrange points. The study of Jupiter Trojans is crucial for testing different models of planet formation that are directly related to our understanding of solar system evolution. In this work, we select known Jupiter Trojans listed by the Minor Planet Center from the full six years data set (Y6) of the Dark Energy Survey (DES) to analyze their photometric properties. The DES data allow us to study Jupiter Trojans with a fainter magnitude limit than previous studies in a homogeneous survey withgrizband measurements. We extract a final catalog of 573 unique Jupiter Trojans. Our sample include 547 asteroids belonging to L5. This is one of the largest analyzed samples for this group. By comparing with the data reported by other surveys we found that the color distribution of L5 Trojans is similar to that of L4 Trojans. We find that L5 Trojans’g−iandg−rcolors become less red with fainter absolute magnitudes, a trend also seen in L4 Trojans. Both the L4 and L5 clouds consistently show such a color–size correlation over an absolute magnitude range 11 <H< 18. We also use DES colors to perform taxonomic classifications. C- and P-type asteroids outnumber D-type asteroids in the L5 Trojans DES sample, which have diameters in the 5–20 km range. This is consistent with the color–size correlation. 

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3. Synthetic Detections of Interstellar Objects with the Rubin Observatory Legacy Survey of Space and Time

   https://doi.org/10.3847/PSJ/ad08c1  

   Marčeta, Dušan; Seligman, Darryl Z. (December 2023, The Planetary Science Journal)

   Abstract The discovery of two interstellar objects passing through the solar system, 1I/‘Oumuamua and 2I/Borisov, implies that a galactic population exists with a spatial number density of order ∼0.1 au⁻³. The forthcoming Rubin Observatory Legacy Survey of Space and Time (LSST) has been predicted to detect more asteroidal interstellar objects like 1I/‘Oumuamua. We apply recently developed methods to simulate a suite of galactic populations of interstellar objects with a range of assumed kinematics, albedos, and size–frequency distributions (SFDs). We incorporate these populations into the objectsInField algorithm, which simulates detections of moving objects by an arbitrary survey. We find that the LSST should detect between ∼0 and 70 asteroidal interstellar objects every year (assuming the implied number density), with sensitive dependence on the SFD slope and characteristic albedo of the host population. The apparent rate of motion on the sky—along with the associated trailing loss—appears to be the largest barrier to detecting interstellar objects. Specifically, a relatively large number of synthetic objects would be detectable by the LSST if not for their rapid sky motion (>0.°5 day⁻¹). Therefore, algorithms that could successfully link and detect rapidly moving objects would significantly increase the number of interstellar object discoveries with the LSST (and in general). The mean diameter of detectable, inactive interstellar objects ranges from ∼50 to 600 m and depends sensitively on the SFD slope and albedo. 

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4. From Centaurs to Comets - 40 years

   https://doi.org/10.1016/B978-0-12-816490-7.00014-X  

   Peixinho, Nuno; Thirouin, Audrey; Tegler, Stephen C.; Di Sisto, Romina; Delsanti, Audrey; Guilbert-Lepoutre, Aurélie; Bauer, James G. (January 2020, Elsevier)

   Review chapter to be published in the book "The Transneptunian Solar System", Editors: Dina; doi:10.1016/B978-0-12-816490-7.00014-X (Ed.)

   In 1977, while Apple II and Atari computers were being sold, a tiny dot was observed in an inconvenient orbit. The minor body 1977 UB, to be named (2060) Chiron, with an orbit between Saturn and Uranus, became the first Centaur, a new class of minor bodies orbiting roughly between Jupiter and Neptune. The observed overabundance of short-period comets lead to the downfall of the Oort cloud as exclusive source of comets and to the rise of the need for a Trans-Neptunian comet belt. Centaurs were rapidly seen as the transition phase between Kuiper belt objects, also known as Trans-Neptunian objects (TNOs) and the Jupiter-family comets (JFCs). Since then, a lot more has been discovered about Centaurs: They can have cometary activity and outbursts, satellites, and even rings. Over the past four decades since the discovery of the first Centaur, rotation periods, surface colors, reflectivity spectra, and albedos have been measured and analyzed. However, despite such a large number of studies and complementary techniques, the Centaur population remains a mystery as they are in so many ways different from the TNOs and even more so from the JFCs. 

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5. Performance Assessment of Four Data-Driven Machine Learning Models: A Case to Generate Sentinel-2 Albedo at 10 Meters

   https://doi.org/10.3390/rs15102684  

   Chen, Hao; Lin, Xingwen; Sun, Yibo; Wen, Jianguang; Wu, Xiaodan; You, Dongqin; Cheng, Juan; Zhang, Zhenzhen; Zhang, Zhaoyang; Wu, Chaofan; et al (May 2023, Remote Sensing)

   High-resolution albedo has the advantage of a higher spatial scale from tens to hundreds of meters, which can fill the gaps of albedo applications from the global scale to the regional scale and can solve problems related to land use change and ecosystems. The Sentinel-2 satellite provides high-resolution observations in the visible-to-NIR bands, giving possibilities to generate a high-resolution surface albedo at 10 m. This study attempted to evaluate the performance of the four data-driven machine learning algorithms (i.e., random forest (RF), artificial neural network (ANN), k-nearest neighbor (KNN), and XGBoost (XGBT)) for the generation of a Sentinel-2 albedo over flat and rugged terrain. First, we used the RossThick-LiSparseR model and the 3D discrete anisotropic radiative transfer (DART) model to build the narrowband surface reflectance and broadband surface albedo, which acted as the training and testing datasets over flat and rugged terrain. Second, we used the training and testing datasets to drive the four machine learning models, and evaluated the performance of these machine learning models for the generation of Sentinel-2 albedo. Finally, we used the four machine learning models to generate a Sentinel-2 albedo and compared them with in situ albedos to show the models’ application potentials. The results show that these machine learning models have great performance in estimating Sentinel-2 albedos at a 10 m spatial scale. The comparison with in situ albedos shows that the random forest model outperformed the others in estimating a high-resolution surface albedo based on Sentinel-2 datasets over the flat and rugged terrain, with an RMSE smaller than 0.0308 and R2 larger than 0.9472. 

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