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Register a new userAstrocladistics of the Jovian Trojan Swarms
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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.
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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.
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.
The one-meter telescope-reflector `Saturn (D=1 m, F = 4 m) was partially renovated at the Pulkovo observatory at the end of 2014. The telescope was equipped by CCD camera S2C with 14x14 arcmin field of view and 824 mas per pix scale. The observations of outer Jovian satellites have been performed in a test mode since January 2015. The exposure time of 30 seconds allows us to obtain images of stars up to magnitude 19.5 with the present state of the mirror and the equipment. The observations of outer Jovian satellites have been performed during testing period. These objects are interesting targets because their astrometric observations required to improve ephemeris and dynamic studies. Satellites positions have been determined on the basis of CCD images obtained within 6 nights. Astrometric reduction is performed by linear method using HCRF/UCAC4 and HCRF/URAT1. Internal accuracy of satellites positions has been estimated as 20 - 100 mas. The absolute values of residuals O-C do not exceed 100 mas in most cases. The independent tests have been carried out by the direct comparison with the results of observations of the Jovian satellite Himalia performed simultaneously by the Normal astrograph (the largest difference was 113 mas). This work has been partially supported by RFBR (12-02-00675-a) and the 22 Program of RAS Praesidium.
New observations of Jupiters decametric radio emissions have been made with the Long Wavelength Array Station 1 (LWA1) which is capable of making high quality observations as low as 11 MHz. Full Stokes parameters were determined for bandwidths of 16 MHz. Here we present the first LWA1 results for the study of six Io-related events at temporal resolutions as fine as 0.25 ms. LWA1 data show excellent spectral detail in Jovian DAM such as simultaneous left hand circular (LHC) and right hand circular (RHC) polarized Io-related arcs and source envelopes, modulation lane features, S-bursts structures, narrow band N-events, and interactions between S-bursts and N-events. The sensitivity of the LWA1 combined with the low radio frequency interference environment allow us to trace the start of the LHC Io-C source region to much earlier CMLIII than typically found in the literature. We find the Io-C starts as early as CMLIII = 230 degrees at frequencies near 11 MHz. This early start of the Io-C emission may be valuable for refining models of the emission mechanism. We also detect modulation lane structures that appear continuous across LHC and RHC emissions, suggesting that both polarizations may originate from the same hemisphere of Jupiter. We present a study of rare S-bursts detected during an Io-D event and show drift rates are consistent with those from other Io-related sources. Finally, S-N burst events are seen in high spectral and temporal resolution and our data strongly support the co-spatial origins of these events.
The Trojan asteroids of Jupiter and Neptune are likely to have been captured from original heliocentric orbits in the dynamically excited (hot) population of the Kuiper belt. However, it has long been known that the optical color distributions of the Jovian Trojans and the hot population are not alike. This difference has been reconciled with the capture hypothesis by assuming that the Trojans were resurfaced (for example, by sublimation of near-surface volatiles) upon inward migration from the Kuiper belt (where blackbody temperatures are $sim$40 K) to Jupiters orbit ($sim$125 K). Here, we examine the optical color distribution of the textit{Neptunian} Trojans using a combination of new optical photometry and published data. We find a color distribution that is statistically indistinguishable from that of the Jovian Trojans but unlike any sub-population in the Kuiper belt. This result is puzzling, because the Neptunian Trojans are very cold (blackbody temperature $sim$50 K) and a thermal process acting to modify the surface colors at Neptunes distance would also affect the Kuiper belt objects beyond, where the temperatures are nearly identical. The distinctive color distributions of the Jovian and Neptunian Trojans thus present us with a conundrum: they are very similar to each other, suggesting either capture from a common source or surface modification by a common process. However, the color distributions differ from any plausible common source population, and there is no known modifying process that could operate equally at both Jupiter and Neptune.
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