DPS 2001 meeting, November 2001
Session 25. Solar System Origins II
Oral, Chairs: M. Drake, H. Levison, Wednesday, November 28, 2001, 5:00-6:30pm, Regency GH

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[25.07] On the Controversy between Observations and Dynamical Modelling of Capturing Trojans by a Growing Proto-Jupiter

F. Marzari (Univ. of Padova, Italy), H. Scholl (Observatoire de Nice, France)

According to a widely accepted scenario, planetesimals were trapped in the Jupiter Trojan regions around L4 and L5 due to the changing gravity field induced by the mass growth of proto--Jupiter. Dynamical models yield final orbits for the captured Trojans with large libration amplitudes and low inclinations. The observed Trojan orbits are instead on low libration--high inclination orbits. We have studied complementary dynamical and physical processes that can reconcile the predictions of the mass growth model for the capture of Trojans with observations.

Mutual collisions between planetesimals surrounding the growing Jupiter cause early trapping into Trojans orbits of numerous bodies, as predicted theoretically by Shoemaker et al (1989). During the final rapid growth of Jupiter by gas infall, the libration amplitudes of the orbits of these bodies are reduced by the shrinking of the zero--velocity curves around the Lagrangian points. Even the coupling of collisional effects and mass growth is able to produce a population of small librators. We will show the results of numerical simulations that include both the effects of collisions, mass growth of the planet, and gas drag. The efficiency of the mechanism is also estimated.

The high inclinations of Jupiter Trojans are not well understood. If Trojans were bodies trapped from the planetesimal disk, they should have conserved their primordial low inclination. Which mechanism stirred up their inclinations? It has been suggested that secular resonances can contribute to generate highly inclined bodies (Marzari and Scholl, 2000). Alternatively, large planetary embryos which formed during the runaway growth in the Jupiter region may have excited the inclinations of the Trojans by close encounters and collisions similar to the mechanism described by Petit et al. (1999) for the main belt asteroids. After a few million years, these big embryos escaped from the Trojan swarms either by natural instability or by dynamical friction. We discuss the implications of this model.

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