36th DPS Meeting, 8-12 November 2004
Session 44 Origins and Planet Formation: Satellite Formation
Oral, Friday, November 12, 2004, 10:30am-12:00noon, Clark

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[44.08] Understanding the orbital configuration of the outer planets

K. Tsiganis, A. Morbidelli (OCA / CNRS, Nice), H.F. Levison (SWRI, Boulder), R. Gomes (ON, Brazil)

It is now accepted that the orbits of the outer planets changed significantly during the epoch of planetary migration, as they interacted with an external disk of planetesimals. Two types of migration have been suggested so far: (i) smooth migration of an initially extended system embedded in a low-mass disk (Fernandez and Ip, 1984), or (ii) encounters among the planets of an initially compact system, subsequently stabilized by a high-mass disk (Thommes et al., 1999). Both models have disadvantages and generally fail to reproduce the planetary orbits, especially the eccentricities of Jupiter and Saturn.

Here we present numerical simulations, which strongly support an intermediate case: an initially compact system (within 15 AU) of planets on nearly circular and coplanar orbits is assumed. The interplanetary region is cleared of planetesimals and a 30-50 Earth masses disk extends up to 30-35 AU. As the planets begin to migrate, several resonant configurations between two planets may be encountered. In particular, when Jupiter and Saturn cross the 1/2 mean motion resonance a qualitative change in the dynamics occurs. The divergent crossing directions for the two planets, forces their orbits to become eccentric, by 5% and 10% respectively. Depending on the relative positions of Uranus and Neptune at that time, a phase of encounters, primarily among the ice giants, may follow. In most simulations the system survives this instability, which excites the disk and increases the rate of migration. The disk is depleted within 200 Myrs and the planets reach a final configuration, which closely resembles the currently observed one. Our simulations show that, at the time when the instability occurs, an intense flux of comets and asteroids towards the inner solar system begins.

Fernandez J.A. and W.H. Ip (1984), Icarus 58, 109.

Thommes E.W., Duncan M.J. and H.F. Levison (1999), Nature 402, 635.

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Bulletin of the American Astronomical Society, 36 #4
© 2004. The American Astronomical Soceity.