We present updated/new thermal model fits for 478 Jovian Trojan asteroids observed with the Wide-field Infrared Survey Explorer (WISE) Using the fact that the two shortest bands used by WISE, centered on 34 and 46 μm, are dominated by reflected light, we derive albedos of a significant fraction of these objects in these bands While the visible albedos of both the C-, P-, and D-type asteroids are strikingly similar, the WISE data reveal that the albedo at 34 μm is different between C-/P- and D-types The albedo at 34 μm can thus be used to classify the objects, with C-/P-types having values less than 10% and D-types have values larger than 10% Classifying all objects larger than 50 km shows that the D-type objects dominate both the leading cloud (L 4), with a fraction of 84%, and trailing cloud (L 5), with a fraction of 71%-80% The two clouds thus have very similar taxonomic distribution for these large objects, but the leading cloud has a larger number of these large objects, L 4/L 5 = 134 The taxonomic distribution of the Jovian Trojans is found to be different from that of the large Hildas, which is dominated by C- and P-type objects At smaller sizes, the fraction of D-type Hildas starts increasing, showing more similarities with the Jovian Trojans If this similarity is confirmed through deeper surveys, it could hold important clues to the formation and evolution of the two populations The Jovian Trojans does have similar taxonomic distribution to that of the Jovian irregular satellites, but lacks the ultra red surfaces found among the Saturnian irregular satellites and Centaur population

http://iopscience.iop.org/article/10.1088/0004-637X/759/1/49/pdf

Wise/neowise observations of the jovian trojan population: taxonomy

I have computed proper elements for 174 asteroids in the 1: 1 resonance with Jupiter, that is for all the reliable orbits available (numbered and multi-opposition). The procedure requires numerical integration, under the perturbations by the four major planets, for 1,000,000 years; the output is digitally filtered and compressed into a“synthetic theory” (as defined within the LONGSTOP project). The proper modes of oscillation of the variables related to eccentricity, perihelion, inclination and node define proper elements. A third proper element is defined as the amplitude of the oscillation of the semimajor axis associated with the libration period; because of the strong nonlinearity of the problem, this component cannot be determined by a simple Fourier transform to the frequency domain. I therefore give another definition, which results in very good stability with time. For 87% of the computed orbits, the stability of the proper elements-at least over 1 Myr- is within the following bounds: 0.001 AU in semimajor axis, 0.0025 in eccentricity and sine of inclination. Half of the cases with degraded stability of the proper elements are found to be chaotic, with e-folding times between 16,000 and 660, 000 yr; in some other cases, chaotic behaviour does not result in a significantly decreased stability of the proper elements (stable chaos). The accuracy and stability of these proper elements is good enough to allow a search for asteroid families; however, the dynamical structure of the Trojan belt is very different from the one of the main belt, and collisional events among Trojans can result in a distribution of fragments difficult to identify. The occurrence of couples of Trojans with very close proper elements is proven not to be statistically significant in almost all cases. As the only exception, the couple 1583 Antilochus — 3801 Thrasimedes is significant; however, it is not easy to account for it by a conventional collisional theory. The Menelaus group is confirmed as a strong candidate collisional family; Teucer and Sarpedon could be considered as significant clusters. A number of other clumps are detected (by the same automated clustering method used for the main belt by Zappala et al., 1990,1992), but the total number of Trojans with reliable orbits is not large enough to detect many significant candidate families.

The Trojan Asteroid Belt: Proper Elements, Stability, Chaos and Families

The 0.91-m ‘Spacewatch Telescope’ of the Steward Observatory of the University of Arizona on Kitt Peak is dedicated to scanning with charge-coupled devices (CCDs) during the dark half of the month. We explored six modes of using CCDs for searches of gamma-ray bursters, debris in geosynchronous space, satellites of asteroids, brown dwarfs, the tenth planet, comets, cometesimals, and various types of asteroids. In the process, we gained experience with cosmic rays and artifacts in CCD observations. Each of these topics is described. I especially note that the existence of cometesimals has not been confirmed by the Spacewatch Telescope, contrary to reports published by others. This paper describes a new discipline in astrophysics, ’scannerscopy’, of surveying with a CCD rather than with photography at a Schmidt telescope. It uses the CCD in scanning rather than in sequencing of stare exposures as is done at most observatories. This may save telescope time, and flat-fielding is rarely needed. Usually we turn the drive off, but the scanning can be done with the telescope moving. In any case, the motion on the sky is precisely followed by slaving the charge transfer of the CCD to the drift rate of the image, while the CCD is read out continuously during the observing. Our primary application of CCD scanning is on moving objects such as comets and asteroids. We also do routine astronomy with CCDs, in a transit method, and this yields a precision of better than ±0.7 arc sec. We presently use a Tektronix 2048×2048 CCD, 38 arc min wide, to a limiting magnitude ofV=20.5 (6σ detection). This is successful even for discovering rare and small near-Earth asteroids. 1990 UN with a diameter of 90 m and 1991 BA at 9 m are the smallest natural objects observed outside the Earth's atmosphere to date. In a month with good conditions we find typically 2000 new main-belt asteroids and, on average, nearly two near-Earth asteroids. Only the latter are followed up with astrometry. The goal is to study magnitude-frequency relations, as well as to complete the inventory of dangerous impactors on Earth. We are designing a new CCD-scanning telecope to become an order-of-magnitude more effective in the discovery of elusive objects than the Spacewatch Telescope. The paper also describes possibilities with cameras on spacecraft that pass through the asteroid belt; thousands of small asteroids can be observed with the CCDs of CRAF and CASSINI.

Scanning with charge-coupled devices

Observational Selection Effects in Asteroid Surveys and Estimates of Asteroid Population Sizes

Jupiter’s irregular satellites possess large, eccentric and highly inclined orbits. They are conventionally considered separately from the temporarily captured satellites and the Trojans (the latter co-orbiting the Sun leading and trailing Jupiter by 60◦). However, there is reason to believe that objects in these three groups share many similarities, both in terms of their physical properties and their origins. Accordingly, in this review we jointly discuss the irregular and temporary satellites and the Trojans. In the modern view of the solar system, different populations of small bodies can be traced back to their origin in the protoplanetary disk of the Sun. Most planetesimals that formed near the orbits of the giant planets were promptly ejected from the planetary region. A small fraction of those ejected (perhaps 10%) remain bound to the Sun in the ∼ 10 AU scale Oort Cloud which provides a continuing source of the long-period comets. Planetesimals growing beyond Neptune were relatively undisturbed and their descendants survive today in the Kuiper Belt . The Kuiper Belt in turn feeds the giant-planet crossing Centaurs , which are then converted by planetary (largely Jovian) perturbations into Jupiter Family Comets (JFCs; short-period comets which are strongly interacting with Jupiter, formally those with Tisserand invariants 2 ≤ T ≤ 3). During their interaction with Jupiter, the comets sometimes become temporarily trapped. Main-belt asteroids near resonances with Jupiter can also be excited into Jupiter-crossing orbits, and may contribute to the populations of temporarily trapped objects. Since there is currently no effective source of energy dissipation, neither the temporary satellites nor the Trojan librators can be captured as permanent members of these populations. Temporary members will be either flung out of the jovian system or impact the planet or one of the Galilean satellites. However, at very early epochs, at the end of Jupiter’s ≤ 10 to ≤ 10 yr growth phase, several mechanisms might have operated to permanently trap objects from these and other reservoirs. Therefore, populations which are not now interacting may once have been so. Given the dynamical interrelations (Figure 12.1), it is to be expected that Figure 12.1. Interrelations among the populations considered in this chapter. Solid arrows denote established dynamical pathways. At the present epoch, in which sources of energy dissipation are essentially absent, no known pathways (dashed lines) exist between the temporary and permanent satellite and Trojan populations. Numbers in parentheses indicate the approximate dynamical lifetimes of the different populations.

/pdf/jupiter-s-outer-satellites-and-trojans-1g2zqhv1sv.pdf

Jupiter's Outer Satellites and Trojans

https://scholarlypublications.universiteitleiden.nl/access/item%3A2715080/view

The second Palomar-Leiden Trojan survey

Une etude d'observations photographiques d'asteroides a permis de trouver 1491 asteroides dont les elements orbitaux peuvent etre determines (publies dans Mina Planet Circulars, 12536-12560, 5 decembre 1987). Pour les asteroides de ce programme, la densite du champ d'asteroides comme fonction de la latitude est determinee et la nature de 32 asteroides (Trojan, type Hungaria ou type Hilda) est trouvee

/pdf/the-1977-palomar-leiden-trojan-survey-ykv5cuo1u6.pdf

M. Wisse-Schouten

Papers

The second Palomar-Leiden Trojan survey

The 1977 Palomar-Leiden Trojan survey