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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[25.06] Capture of Trojan Asteroids in the Early Solar Nebula

S.J. Kortenkamp, D.P. Hamilton (University of Maryland, Dept. of Astronomy)

Planetesimals scattered onto high eccentricity orbits by Jupiter experienced very severe energy dissipation due to gas drag from the solar nebula. Numerical modeling shows that this damping can alter some orbits rapidly enough to prevent subsequent encounters with the planet. A small but significant fraction (<8%) of scattered planetesimals find safe harbor on horseshoe and tadpole orbits in 1:1 resonance with the planet. Capture of these Trojan precursors depends strongly on the mass and orbital eccentricity of the planet as well as the planetesimal masses. A 10 Earth-mass protoplanetary core is much more efficient at capturing planetesimals into 1:1 resonance than a full-size 318 Earth-mass Jupiter---all other parameters being equal. Because small planetesimals experience a stronger drag force than larger bodies, after the initial scattering event they evolve more rapidly and are thus better protected from a second planetary encounter. Thus small bodies have a greater chance at becoming permanently trapped into 1:1 resonance than larger bodies do.

For high planetary orbital eccentricities (e>0.2), a number of interesting features appear. First, capture probabilities into the 1:1 resonance appear to be an increasing function of planetary eccentricity. In additon, with high planetary eccentricity, nearly all scattered planetesimals are trapped in or evolve into L5 tadpole orbits that trail the planet, as was noted by Peale (1993). Finally, we find examples of direct capture into distant pseudo-satellite orbits of the planet (for e>0.15). These strange orbits circle both the planet and the Sun with Jupiter's 12 year period, and may be the precurors of the planet's large population of irregular satellites.

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