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TOPIC: Neptune Trojans


L

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RE: Neptune Trojans
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Title: The Neptune Trojans - a new source for the Centaurs?
Authors: J. Horner, P. S. Lykawka
(Version v3)

The fact that the Centaurs are the primary source of the Short Period Comets is well established. However, the origin of the Centaurs themselves is still under some debate, with a variety of different source reservoirs being proposed in the last decade. In this work, we suggest that the Neptune Trojans (together with the Jovian Trojans) could represent an additional significant source of Centaurs. Using dynamical simulations of the first Neptune Trojan discovered (2001 QR322), together with integrations following the evolution of clouds of theoretical Neptune Trojans obtained during simulations of planetary migration, we show that the Neptune Trojan population contains a great number of objects which are unstable on both Myr and Gyr timescales. Using individual examples, we show how objects that leave the Neptunian Trojan cloud evolve onto orbits indistinguishable from those of the known Centaurs, before providing a range of estimates of the flux from this region to the Centaur population. With only moderate assumptions, it is shown that the Trojans can contribute a significant proportion of the Centaur population, and may even be the dominant source reservoir. This result is supported by past work on the colours of the Trojans and the Centaurs, but it will take future observations to determine the full scale of the contribution of the escaped Trojans to the Centaur population.

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L

Posts: 131433
Date:
2001 QR322
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Title: 2001 QR322: a dynamically unstable Neptune Trojan?
Authors: J. Horner, P. S. Lykawka
(Version v2)

Since early work on the stability of the first Neptunian Trojan, 2001 QR322, suggested that it was a dynamically stable, primordial body, it has been assumed this applies to both that object, and its more recently discovered brethren. However, it seems that things are no longer so clear cut. In this work, we present the results of detailed dynamical simulations of the orbital behaviour of 2001 QR322. Using an ephemeris for the object that has significantly improved since earlier works, we follow the evolution of 19683 test particles, placed on orbits within the observational error ellipse of 2001 QR322's orbit, for a period of 1 Gyr. We find that majority of these "clones" of 2001 QR322 are dynamically unstable, exhibiting a near-exponential decay from both the Neptunian Trojan cloud (decay halflife ~550 Myr) and the Solar system (decay halflife ~590 Myr). The stability of the object within Neptune's Trojan cloud is found to be strongly dependent on the initial semi-major axis used, with those objects located at semimajor axis equal or greater than 30.30 AU being significantly less stable than those interior to this value, as a result of their having initial libration amplitudes very close to a critical threshold dividing regular and irregular motion, located at ~70-75 deg (full extent of angular motion). This result suggests that, if 2001 QR322 is a primordial Neptunian Trojan, it must be a representative of a population that was once significantly larger than that we see today, and adds weight to the idea that the Neptune Trojans may represent a significant source of objects moving on unstable orbits between the giant planets (the Centaurs).

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L

Posts: 131433
Date:
Neptune Trojans
Permalink  
 


Title: The Neptune Trojans - a new source for the Centaurs?
Authors: J. Horner, P. S. Lykawka

The fact that the Centaurs are the primary source of the Short Period Comets is well established. However, the origin of the Centaurs themselves is still under some debate, with a variety of different source reservoirs being proposed in the last decade. In this work, we suggest that the Neptune Trojans (together with the Jovian Trojans) could represent an additional significant source of Centaurs. Using dynamical simulations of the first Neptune Trojan discovered (2001 QR322), together with integrations following the evolution of clouds of theoretical Neptune Trojans obtained during simulations of planetary migration, we show that the Neptune Trojan population contains a great number of objects which are unstable on both Myr and Gyr timescales. Using individual examples, we show how objects that leave the Neptunian Trojan cloud evolve onto orbits indistinguishable from those of the known Centaurs, before providing a range of estimates of the flux from this region to the Centaur population. With only moderate assumptions, it is shown that the Trojans can contribute a significant proportion of the Centaur population, and may even be the dominant source reservoir. This result is supported by past work on the colours of the Trojans and the Centaurs, but it will take future observations to determine the full scale of the contribution of the escaped Trojans to the Centaur population.

Read more (4554kb, PDF)

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Title: The Dynamics of Neptune Trojan: I. the Inclined Orbits
Authors: Li-Yong Zhou (1), Rudolf Dvorak (2), Yi-Sui Sun (1) ((1) Department of Astronomy, Nanjing University, China (2) Institute for Astronomy, University of Vienna, Austria)

The stability of Trojan type orbits around Neptune is studied. As the first part of our investigation, we present in this paper a global view of the stability of Trojans on inclined orbits. Using the frequency analysis method based on the FFT technique, we construct high resolution dynamical maps on the plane of initial semimajor axis a_0 versus inclination i_0. These maps show three most stable regions, with i_0 in the range of (0,12), (22,36) and (51,59) respectively, where the Trojans are most probably expected to be found. The similarity between the maps for the leading and trailing triangular Lagrange points L_4 and L_5 confirms the dynamical symmetry between these two points. By computing the power spectrum and the proper frequencies of the Trojan motion, we figure out the mechanisms that trigger chaos in the motion. The Kozai resonance found at high inclination varies the eccentricity and inclination of orbits, while the \nu_8 secular resonance around i_0 ~44 pumps up the eccentricity. Both mechanisms lead to eccentric orbits and encounters with Uranus that introduce strong perturbation and drive the objects away from the Trojan like orbits. This explains the clearance of Trojan at high inclination (>60) and an unstable gap around 44 on the dynamical map. An empirical theory is derived from the numerical results, with which the main secular resonances are located on the initial plane of (a_0,i_0). The fine structures in the dynamical maps can be explained by these secular resonances.

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