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Some remarks on the early evolution of Enceladus

机译：关于土卫二早期演变的一些评论

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Thermal history of Enceladus is investigated from the beginning of accretion to formation of its core (similar to 400 My). We consider model with solid state convection (in a solid layer) as well as liquid state convection (in molten parts of the satellite). The numerical model of convection uses full conservative finite difference method. The roles of two modes of convection are considered using the parameterized theory of convection. The following heat sources are included: short lived and long lived radioactive isotopes, accretion, serpentinization, and phase changes. Heat transfer processes are: conduction, solid state convection, and liquid state convection. It is found that core formation was completed only when liquid state convection had slowed down. Eventually, the porous core with pores filled with water was formed. Recent data concerning gravity field of Enceladus confirm low density of the core. We investigated also thermal history for different values of the following parameters: time of beginning of accretion t(ini), duration of accretion t(acr), viscosity of ice close to the melting point eta(m), activation energy in formula for viscosity E, thermal conductivity of silicate component k(sil), ammonia content X-NH3, and energy of serpentinization c(serp). All these parameters are important for evolution, but not dramatic differences are found for realistic values. Moreover, the hypothesis of proto-Enceladus (stating that initially Enceladus was substantially larger) is considered and thermal history of such body is calculated. The last subject is the Mimas-Enceladus paradox. Comparison of thermal models of Mimas and Enceladus indicates that period favorable for 'excited path of evolution' was significantly shorter for Mimas than for Enceladus. (C) 2014 Elsevier Ltd. All rights reserved.
机译：从增加开始到形成核心（类似于400 My）研究了Enceladus的热史。我们考虑具有固态对流（在固体层中）以及液态对流（在卫星的熔融部分中）的模型。对流数值模型采用完全保守的有限差分法。使用参数化对流理论来考虑两种对流模式的作用。包括以下热源：短寿命和长寿命放射性同位素，吸积，蛇形化和相变。传热过程为：传导，固态对流和液态对流。发现仅在液态对流减慢时才完成岩心形成。最终，形成具有填充有水的孔的多孔核。有关土卫二重力场的最新数据证实岩心密度低。我们还研究了以下参数的不同值的热历史：吸积开始时间t（ini），吸积持续时间t（acr），接近熔点eta（m）的冰的粘度，粘度公式中的活化能E，硅酸盐组分k（sil）的热导率，氨含量X-NH3，蛇纹石化能量c（serp）。所有这些参数对于进化都很重要，但对于实际值并没有发现显着差异。此外，考虑了原始土卫二的假设（指出土卫二最初的体积大得多），并计算了该土体的热史。最后一个主题是Mimas-Enceladus悖论。比较Mimas和Enceladus的热模型表明，Mimas的“激动的进化路径”有利时期明显短于Enceladus。 （C）2014 Elsevier Ltd.保留所有权利。

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