THE DYNAMICAL EVOLUTION OF ESCAPED TROJAN ASTEROIDS

DI SISTO, ROMINA P.; X. S. RAMOS; GALLARDO, TABARE

Montevideo

Congreso; Asteroid Comets Meteors 2017; 2017

Introduction: Jupiter Trojan asteroids have been widely studied both from a dynamical point of view and through their physical properties. They are the group of asteroids located in the Lagrangian points L4 and L5 of Jupiter and therefore, on 1:1 mean motion resonance with the planet. It is an important asteroidal population both in number and also in relation to their dynamical and physical properties. Since their discovery, an asymmetry in the number of Trojans located in L4 and L5 was noted, i.e, the number of L4 Trojans is a factor of ~1.5 the number in L5 [1], and this asymmetry continues to date. This problem is not yet well Understood, although some theories have been proposed. Although Trojans are located in stable orbits, it is likely that some of them may escapefrom the resonance over time [2] [3] and become part of other minor body populations of the Solar System. In this contribution we study the dynamical evolution of Jupiter Trojan asteroids focusing on the evolution of the asteroids when they escape from the resonance. Methods: This work is carried out through numerical simulations. The orbits of current numbered Trojan asteroids are taken as initial conditions and their evolution for 4.5 Gyr is followed under the gravitational action of the Sun and the planets from Venus to Neptune. The encounters of Trojans with the planets are registered. The time of the first encounter is considered as the "escape time" and the Trojan would be an "escaped Trojan"; its subsequent evolution through the Solar System up to a collision or escape will be the objective of this contribution. Results: We find the rate of escape of Trojans from L5, ~ 1.1 times greater than from L4. The majority of escaped Trojans have encounters with Jupiter although they have encounters with the other planets too. The mean lifetime of escaped Trojans in the Solar System is 3.5 My for L4 and ~0.7 My for L5, being then the evolution of escaped L4 Trojans slower than that of L5 Trojans. We built ?occupancy maps? (Fig. 1) that represent the zones in the Solar System where escaped Trojans should be found. The color code is indicative of the permanence time spent in each zone (blue for most visited regions, red for least visited). Then, those plots form dynamical maps of ``permanence'' in the different zones of the Solar System and give a general idea of the regions visited by escaped Trojans. Almost all escaped Trojans become part of JFCs and Centaurs, but the contributionfrom L4 is different than the contribution from L5. For example, meanwhile L5 escapees concentrate towards the inner regions inward theorbit of Neptune, L4 escapees have preferentially a > 30 AU. It is notable that the proportional number of collisions by L4 escapees is three times greater than that of L5 escapees.