Astronomy and Astrophysics – Astronomy
Scientific paper
Sep 1999
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1999dda....31.0303k&link_type=abstract
American Astronomical Society, DDA meeting #31, #03.03
Astronomy and Astrophysics
Astronomy
Scientific paper
Most conventional models of planet formation begin with a protoplanetary disk of gas and dust orbiting a central protostar. During the early evolution of this disk it is believed that the dust particles coagulate into larger planetesimals in the 0.1 to 10 kilometer size-range. In a swarm of such planetesimals gas drag and mutual gravitational interactions become important factors in the continued growth of the bodies. The mutual gravitational interactions effectively randomize the orientation of the planetesimal orbits (longitudes of pericenter and node) and nearly all modeling of the growth of planetesimals into planetary embryos relies on this assumption of randomized orientation. However, this fundamental assumption may not be valid in protoplanetary systems which include massive companions such as stars, brown dwarfs or early-formed giant planets. In the model we are currently investigating we assume Jupiter and Saturn formed quickly ( ~ 10(2) years) via disk instabilities (Boss, ApJ 503, 923, 1998) rather than the conventional core-accretion mechanism ( ~ 10(6) to 10(7) years). Gas drag and secular perturbations combine to produce size-dependent forced orbital elements for planetesimals of different sizes at the same semi-major axis. Similar sized bodies evolve in phase and have relatively low encounter velocities despite their moderately high forced eccentricities and inclinations. With the passage of time this phase coherence begins to breakdown for two reasons. First, differential secular precession randomizes the orbital phasing over the small range in semi-major axis across which orbital crossing is theoretically possible. Second, if the bodies have grown large enough their random mutual perturbations become comparable to the secular perturbations. The time-scale for these mechanisms depends on the sizes and semi-major axes of the planetesimals and companions. Our current efforts are focused on taking these conditions into account in modeling the growth of planetary embryos near 1 AU and in the asteroid belt.
Kortenkamp Stephen J.
Wetherill George W.
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