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Register a new userBinary Candidates in the Jovian Trojan and Hilda Populations from NEOWISE Lightcurves
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Determining the binary fraction for a population of asteroids, particularly as a function of separation between the two components, helps describe the dynamical environment at the time the binaries formed, which in turn offers constraints on the dynamical evolution of the solar system. We searched the NEOWISE archival dataset for close and contact binary Trojans and Hildas via their diagnostically large lightcurve amplitudes. We present 48 out of 554 Hilda and 34 out of 953 Trojan binary candidates in need of follow-up to confirm their large lightcurve amplitudes and subsequently constrain the binary orbit and component sizes. From these candidates, we calculate a preliminary estimate of the binary fraction without confirmation or debiasing of 14-23% for Trojans larger than ~12 km and 30-51% for Hildas larger than ~4 km. Once the binary candidates have been confirmed, it should be possible to infer the underlying, debiased binary fraction through estimation of survey biases.
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We present the preliminary analysis of 1023 known asteroids in the Hilda region of the Solar System observed by the NEOWISE component of the Wide-field Infrared Survey Explorer (WISE). The sizes of the Hildas observed range from $sim 3 - 200$km. We find no size - albedo dependency as reported by other projects. The albedos of our sample are low, with a weighted mean value $p_V = 0.055pm0.018$, for all sizes sampled by the NEOWISE survey. We observed a significant fraction of the objects in the two known collisional families in the Hilda population. It is found that the Hilda collisional family is brighter, with weighted mean albedo of $p_V = 0.061pm0.011$, than the general population and dominated by D-type asteroids, while the Schubart collisional family is darker, with weighted mean albedo of ($p_V = 0.039pm0.013$). Using the reflected sunlight in the two shortest WISE bandpasses we are able to derive a method for taxonomic classification of $sim 10%$ of the Hildas detected in the NEOWISE survey. For the Hildas with diameter larger than 30km there are $67^{+7}_{-15}%$ D-type asteroids and $26^{+17}_{-5}%$ C-/P-type asteroids (with the majority of these being P-types).
The Jovian Trojans are two swarms of small objects that share Jupiters orbit, clustered around the leading and trailing Lagrange points, L$_4$ and L$_5$. In this work, we investigate the Jovian Trojan population using the technique of astrocladistics, an adaptation of the `tree of life approach used in biology. We combine colour data from WISE, SDSS, Gaia DR2 and MOVIS surveys with knowledge of the physical and orbital characteristics of the Trojans, to generate a classification tree composed of clans with distinctive characteristics. We identify 48 clans, indicating groups of objects that possibly share a common origin. Amongst these are several that contain members of the known collisional families, though our work identifies subtleties in that classification that bear future investigation. Our clans are often broken into subclans, and most can be grouped into 10 superclans, reflecting the hierarchical nature of the population. Outcomes from this project include the identification of several high priority objects for additional observations and as well as providing context for the objects to be visited by the forthcoming textit{Lucy} mission. Our results demonstrate the ability of astrocladistics to classify multiple large and heterogeneous composite survey datasets into groupings useful for studies of the origins and evolution of our Solar system.
We present the preliminary analysis of over 1739 known and 349 candidate Jovian Trojans observed by the NEOWISE component of the Wide-field Infrared Survey Explorer (WISE). With this survey the available diameters, albedos and beaming parameters for the Jovian Trojans have been increased by more than an order of magnitude compared to previous surveys. We find that the Jovian Trojan population is very homogenous for sizes larger than $sim10$km (close to the detection limit of WISE for these objects). The observed sample consists almost exclusively of low albedo objects, having a mean albedo value of $0.07pm0.03$. The beaming parameter was also derived for a large fraction of the observed sample, and it is also very homogenous with an observed mean value of $0.88pm0.13$. Preliminary debiasing of the survey shows our observed sample is consistent with the leading cloud containing more objects than the trailing cloud. We estimate the fraction to be N(leading)/N(trailing) $sim 1.4 pm 0.2$, lower than the $1.6 pm 0.1$ value derived by others.
We present fully covered phased light curves for 56 Jovian Trojan asteroids as acquired by the K2 mission of the Kepler space telescope. This set of objects has been monitored during Campaign 6 and represents a nearly unbiased subsample of the population of small Solar System bodies. We derived precise periods and amplitudes for all Trojans, and found their distributions to be compatible with the previous statistics. We point out, however, that ground-based rotation periods are often unreliable above 20h, and we find an overabundance of rotation periods above 60h compared with other minor planet populations. From amplitude analysis we derive a rate of binarity of 20$pm$ 5%. Our spin rate distribution confirms the previously obtained spin barrier of ~5h and the corresponding ~0.5 g cm$^{-3}$ cometary-like density limit, also suggesting a high internal porosity for Jovian Trojans. One of our targets, asteroid 65227 exhibits a double rotation period, which can either be due to binarity or the outcome of a recent collision.
We present new Hubble Space Telescope and ground-based Keck observations and new Keplerian orbit solutions for the mutual orbit of binary Jupiter Trojan asteroid (617) Patroclus and Menoetius, targets of NASAs Lucy mission. We predict event times for the upcoming mutual event season, which is anticipated to run from late 2017 through mid 2019.
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