ON THE ORIGIN OF PLANETARY SPINS

被引:116
作者
DONES, L [1 ]
TREMAINE, S [1 ]
机构
[1] UNIV TORONTO,CANADIAN INST THEORET ASTROPHYS,MCLENNAN LABS,TORONTO M5S 1A7,ONTARIO,CANADA
关键词
D O I
10.1006/icar.1993.1059
中图分类号
P1 [天文学];
学科分类号
0704 ;
摘要
We examine the rate of accretion of mass and spin angular momentum by a spherical solid body ("planet") immersed in a differentially rotating disk of particles ("planetesimals"). If the planet travels on a circular orbit, the accretion process is described by two dimensionless parameters r and s, which measure the ratio of the planet's radius to its Hill radius and the ratio of the rms radial velocity of the planetesimals to the shear across the Hill radius, respectively. Using a combination of analytic arguments and numerical simulations, we derive the mass and angular momentum accretion rates and their scaling with r and s. By introducing an additional parameter, the effective mass of the planetesimals relative to the planet, we can derive the obliquities and spins arising from the stochastic nature of the accretion process. Our results are consistent with those of previous calculations by J. J. Lissauer and D. M. Kary (Icarus 94, 126-159 (1991)) wherever there is overlap in parameter space. In particular, we conclude that ordered accretion from a uniform or slowly varying disk of small bodies cannot result in rotation as rapid as that of Earth or Mars for any value of the disk velocity dispersion s. The spin rates of these planets are most naturally explained as arising from one or a few "giant" impacts by planetesimals. © 1993 by Academic Press, Inc.
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页码:67 / 92
页数:26
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