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首页> 外文期刊>The Astrophysical Journal. Letters >Compositions and origins of outer planet systems: Insights from the Roche critical density
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Compositions and origins of outer planet systems: Insights from the Roche critical density

机译：外行星系统的组成和起源：罗氏临界密度的见解

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We consider the Roche critical density (ρ_(Roche)), the minimum density of an orbiting object that, at a given distance from its planet, is able to hold itself together by self-gravity. It is directly related to the more familiar "Roche limit," the distance from a planet at which a strengthless orbiting object of given density is pulled apart by tides. The presence of a substantial ring requires that transient clumps have an internal density less than ρ_(Roche). Conversely, in the presence of abundant material for accretion, an orbiting object with density greater than ρ_(Roche) will grow. Comparing the ρ_(Roche) values at which the Saturn and Uranus systems transition rapidly from disruption-dominated (rings) to accretion-dominated (moons), we infer that the material composing Uranus' rings is likely more rocky, as well as less porous, than that composing Saturn's rings. From the high values of ρ_(Roche) at the innermost ring moons of Jupiter and Neptune, we infer that those moons may be composed of denser material than expected, or more likely that they are interlopers that formed farther from their planets and have since migrated inward, now being held together by internal material strength. Finally, the "Portia group" of eight closely packed Uranian moons has an overall surface density similar to that of Saturn's A ring. Thus, it can be seen as an accretion-dominated ring system, of similar character to the standard ring systems except that its material has a characteristic density greater than the local ρ_(Roche).
机译：我们考虑罗氏临界密度（ρ_（Roche）），这是一个轨道物体的最小密度，该物体在距行星一定距离处能够通过自重将自身保持在一起。它与更熟悉的“罗氏极限”直接相关，“罗氏极限”是距行星的距离，在该距离处潮汐将给定密度的无强度轨道物体拉开。实质环的存在要求瞬态团块的内部密度小于ρ_（Roche）。相反，在有大量的增生物质存在的情况下，密度大于ρ_（Roche）的轨道物体将生长。比较土星和天王星系统从扰动为主（环）到吸积为主（月球）的ρ_（Roche）值时，我们推断出组成天王星环的物质可能更坚硬，且孔隙较少，而不是构成土星环的那颗。从木星和海王星最内层环形卫星的ρ_（Roche）的高值，我们可以推断出这些卫星可能由比预期更稠密的物质组成，或者更有可能是与地球距离更远而形成的闯入者，此后便迁移了向内，现在通过内部材料的力量而保持在一起。最后，八颗密密麻麻的乌拉圭卫星的“门廊群”的整体表面密度与土星的A环相似。因此，可以将其视为以吸积为主的环系，其特性与标准环系相似，不同之处在于其材料的特征密度大于局部ρ_（Roche）。

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