[Previous] | [Session 55] | [Next]
S.J. Kortenkamp, D.P. Hamilton (University of Maryland)
Several theories for the origin and evolution of the Trojan asteroids have been proposed over the years. It has been suggested that the Trojans may be comets, escaped satellites of Jupiter, or near-Jupiter planetesimals. A number of mechanisms have been considered for capturing these objects into resonant orbits, including mass accretion and radial migration by Jupiter, collisions between objects, and drag forces. Mass growth and radial migration act directly on Jupiter and indirectly affect its Trojan companions. Forces that act on planetesimals directly are also important; paramount among these is the sun-ward drift of planetesimals due to nebular gas drag.
For a nominal case, we modeled the evolution of planetesimals subject to nebular gas drag and perturbations from a 10 Earth-mass protoplanetary core with moderate eccentricity (e=0.05). Planetesimals of various masses were distributed on circular co-planar orbits external to the core. As their orbits decayed sun-ward, most planetesimals became trapped in external mean-motion resonances with the core. While in theory this trapping may be permanent, trapping lifetime is probably limited by several mechanisms, such as further growth of the core, perturbations from a growing Saturn, and dispersal of the solar nebula. Planetesimals on orbits within about 0.4 AU of the core (for a core at 5.2 AU) are of particular interest. In this region numerous overlapping resonances produce chaotic behavior which allows a significant number (1%) of planetesimals to evolve onto horseshoe and tadpole orbits at the 1:1 resonance. This process involves scattering to high eccentricity orbits followed by severe damping by nebular gas drag. Other cases are being studied using different eccentricities and masses for the core, including a full-size 318 Earth-mass Jupiter. We also plan to explore the effects of a gap in the nebula centered on the core.