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131.
M. R. Bate S. H. Lubow G. I. Ogilvie K. A. Miller 《Monthly notices of the Royal Astronomical Society》2003,341(1):213-229
We analyse the non-linear, three-dimensional response of a gaseous, viscous protoplanetary disc to the presence of a planet of mass ranging from 1 Earth mass (1 M⊕ ) to 1 Jupiter mass (1 MJ ) by using the zeus hydrodynamics code. We determine the gas flow pattern, and the accretion and migration rates of the planet. The planet is assumed to be in a fixed circular orbit about the central star. It is also assumed to be able to accrete gas without expansion on the scale of its Roche radius. Only planets with masses M p ≳ 0.1 MJ produce significant perturbations in the surface density of the disc. The flow within the Roche lobe of the planet is fully three-dimensional. Gas streams generally enter the Roche lobe close to the disc mid-plane, but produce much weaker shocks than the streams in two-dimensional models. The streams supply material to a circumplanetary disc that rotates in the same sense as the orbit of the planet. Much of the mass supply to the circumplanetary disc comes from non-coplanar flow. The accretion rate peaks with a planet mass of approximately 0.1 MJ and is highly efficient, occurring at the local viscous rate. The migration time-scales for planets of mass less than 0.1 MJ , based on torques from disc material outside the Roche lobes of the planets, are in excellent agreement with the linear theory of type I (non-gap) migration for three-dimensional discs. The transition from type I to type II (gap) migration is smooth, with changes in migration times of about a factor of 2. Starting with a core which can undergo runaway growth, a planet can gain up to a few MJ with little migration. Planets with final masses of the order of 10 MJ would undergo large migration, which makes formation and survival difficult. 相似文献
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Interplanetary field enhancements were first discovered in the vicinity of Venus. These events are characterised by an increase in the magnitude of the heliospheric magnetic field with a near-symmetrical, sometimes thorn-shaped profile, and last from minutes to hours. Surveys of the events near Venus and Earth indicated clustering of the events in inertial space, which suggested that their sources were Solar System objects other than the Sun. A survey is presented of strong events of this type detected by the Ulysses spacecraft from 1990 to late 2001. Most of the events are accompanied by a discontinuity in the field direction near the events' centres. Other discontinuities are often symmetrical about the enhancement. The majority of events last less than two hours. When examined as a whole, the events tend to be accompanied by subtle changes in some plasma parameters. The majority of the enhancements are accompanied by magnetic holes on their fringes. The enhancements' occurrence rate increases with decreasing heliocentric distance. Possible formation mechanisms are discussed. No link was found with solar, or solar wind sources. Several aspects of the survey results are consistent with an origin related to cometary dust trails. Possible processes associated with a dust-solar wind interaction are discussed. 相似文献