Gravitational Accretion of Particles onto Moonlets Embedded in Saturn's Rings
Gravitational Accretion of Particles onto Moonlets Embedded in Saturn's Rings
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粒子在嵌入土星环中的小卫星上的引力吸积
DOI：
10.1088/0004-637x/797/2/93
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发表时间：
2014
期刊：
影响因子：
--
通讯作者：
Hiroshi Daisaka
中科院分区：
文献类型：
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作者：
Yuki Yasui;Keiji Ohtsuki;Hiroshi Daisaka
使用本地N体模拟，我们研究引力吸积环粒子到小卫星的核心在土星环。我们发现，重力吸积的粒子到小卫星的核心是不太可能发生在C环，可能很难在内部B环，以及提供的核心是刚性的水冰。粒子吸积对环厚度的依赖性会随着离行星的径向距离和/或粒子密度的变化而变化：前者决定了核心的希尔半径相对于其物理尺寸的大小，而后者则改变了吸积粒子的自引力效应。我们发现，即使环的垂直厚度远小于核心半径，也会发生粒子吸积到核心表面的高纬度区域，尽管在环的外部区域（如外部A环），粒子重新分布到高纬度区域不会完全有效，其中在垂直方向上的核心的希尔球的尺寸显著大于核心的物理半径。我们的研究结果表明，最近从C环中透明洞的观测中推断出的大石头不是由引力吸积局部形成的，而A环中的螺旋桨小卫星将是由粒子吸积到致密核心上形成的引力聚集体。我们的研究结果还表明，土星环外缘附近的小卫星的主体可能已经形成在相当薄的环。
Using a local N-body simulation, we examine gravitational accretion of ring particles onto moonlet cores in Saturn's rings. We find that gravitational accretion of particles onto moonlet cores is unlikely to occur in the C ring and probably difficult in the inner B ring as well provided that the cores are rigid water ice. Dependence of particle accretion on ring thickness changes when the radial distance from the planet and/or the density of particles is varied: the former determines the size of the core's Hill radius relative to its physical size, while the latter changes the effect of self-gravity of accreted particles. We find that particle accretion onto high-latitude regions of the core surface can occur even if the rings' vertical thickness is much smaller than the core radius, although redistribution of particles onto the high-latitude regions would not be perfectly efficient in outer regions of the rings such as the outer A ring, where the size of the core's Hill sphere in the vertical direction is significantly larger than the core's physical radius. Our results suggest that large boulders recently inferred from observations of transparent holes in the C ring are not formed locally by gravitational accretion, while propeller moonlets in the A ring would be gravitational aggregates formed by particle accretion onto dense cores. Our results also imply that the main bodies of small satellites near the outer edge of Saturn's rings may have been formed in rather thin rings.