Astronomy and Astrophysics – Astronomy
Scientific paper
Sep 1996
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1996dps....28.1214w&link_type=abstract
American Astronomical Society, DPS meeting #28, #12.14; Bulletin of the American Astronomical Society, Vol. 28, p.1113
Astronomy and Astrophysics
Astronomy
4
Scientific paper
The jovian planets in our system are believed to have formed by accumulation of rock/ice planetesimals into massive solid cores, which then accreted gas from the Solar Nebula. Jupiter is assumed to mark the nebular ``snow line.'' Newly discovered extrasolar planets are too near their stars for condensation of ice in circumstellar disks. It has been suggested that these planets formed at larger distances and migrated inward. Tidal coupling to an evolving accretion disk requires the planet to form very rapidly, simultaneously with the star itself. This scenario has problems with the timescale for core formation. We suggest an alternative migration mechanism compatible with core-accretion formation on a more reasonable timescale. Stochastic accumulation of planetesimals produces multiple cores of would-be planets, with orbital spacings that are large enough to be stable before onset of gas accretion. The increased mass of gas renders their orbits unstable. Isolated pairs would collide and merge. Systems of three interacting planets are chaotic, and can produce more interesting results. We have integrated orbits of such systems, and find the most common outcome is hyperbolic ejection of one planet. The survivors are left in widely separated stable orbits. These have semimajor axes generally well inside and outside the range of starting orbits, and usually have substantial eccentricities. The inner planet often has periastron distance less than 1 AU. Some cases yield ``double jumps,'' with two planets ejected and the survivor with semimajor axis less than 1 AU and periastron less than 0.1 AU. This scenario can account for the eccentric orbits observed for 70 Vir B and HD114762 B. Close circular orbits like 51 Peg B can result when tidal dissipation circularizes a ``star-grazing'' orbit. Somewhat larger circular orbits, e.g., 47 UMa, B could be due to interactions with a residual nebula. Our model predicts that most stars with close massive planets should have additional companions in distant eccentric orbits.
Marzari Francesco
Weidenschilling Stuart J.
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