Other
Scientific paper
Aug 1997
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1997phdt........28s&link_type=abstract
Thesis (PHD). UNIVERSITY OF CALIFORNIA, SANTA CRUZ , Source DAI-B 58/02, p. 752, Aug 1997, 102 pages.
Other
1
Scientific paper
Planet formation was a complex process in which an initial population of sub-micron-sized grains distributed throughout the gaseous solar nebula coalesced to create nine primary planets, several thousand to one hundred thousand kilometers in diameter, with orbital semi-major axes from 0.4 to 40 AU. A large number of moons, with sizes ranging from tens of kilometers for the smallest known moons to 5000 km for Jupiter's Ganymede, accompany the planets. Leftover planetesimals (asteroids and comets), ranging from ~<1 km up to 1000 km, are strewn throughout the solar system. The farthest cometary bodies are thought to orbit as far as 105 AU from the sun, in the Oort cloud, while the known asteroids are concentrated in the asteroid belt at 2-3 AU. Condensation, sublimation, and growth via collisions with small grains are all important physical processes affecting the growth of icy planetesimals beyond the water ice sublimation radius several AU from the sun. A numerical model of the growth of individual planetesimals in the turbulent outer solar nebula has been constructed which includes these processes. Small particles grow to dm- or m-sizes before gas drag pulls them inward, past the water ice sublimation radius, unless there is a concentration of small grains (or other solid particles) in the midplane to provide rapid collisional growth. Turbulence is important in delaying the inward drift of particles, allowing them to grow at large nebular radii. Different mechanisms dominated during the various stages of planetary aggregation. In particular, in a turbulent nebula, turbulence-generated relative velocities between centimeter-sized particles were too high to permit further growth unless surface adhesion forces between particles were large, but electrostatic forces as well as gravitational forces between centimeter-sized particles are too small to bind them together in such an environment. Experiments have been performed which suggest that, in the outer solar nebula, surface frosts of volatile molecules may have provided an adhesion force adequate to prevent aggregate breakup in collisions, allowing aggregates to grow past the meter stage, at which point gravitational interactions began to dominate the subsequent coagulation.
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