论文标题
增生速率和成分对富含冰块的超级地球结构的影响
The Effect of Accretion Rate and Composition on the Structure of Ice-rich Super-Earths
论文作者
论文摘要
可以合理地假设行星的结构及其成分的内部分布取决于其形成历史。因此，我们遵循一个行星从小胚胎通过其随后的进化的生长。我们根据距中央恒星足够大的距离距离的原动性磁盘模型来估计积聚率范围，以使水冰成为主要组成部分。我们假设积聚的材料是硅酸盐岩石和冰的混合物，没有H-He构造，因为积聚时间尺度远远超过了烟囱气体消散所需的时间。我们采用了一个热进化模型，其中包括吸收加热，放射性能量释放以及冰和岩石的分离。以4.6 Gyr的方式以Safronov参数和冰圈比为自由参数，以计算不同参数组合的生长和进化序列。 我们发现最终结构显着取决于两个参数。低初始冰与岩石比和高积聚速率，每种冰速率增加，导致加热速率增加，导致岩石岩的形成，而相反的条件使组合物几乎没有变化，并导致相对较低的内部温度。当形成岩石的岩心时，冰块丰富的外壁仍然包含与冰混合的岩石。我们发现，冰的相当一部分在积聚后蒸发，具体取决于参数，并假设其丢失，因此地球的最终表面组成和块状密度不一定反映了原行星磁盘的组成。
It is reasonable to assume that the structure of a planet and the interior distribution of its components are determined by its formation history. We thus follow the growth of a planet from a small embryo through its subsequent evolution. We estimate the accretion rate range based on a protoplanetary disk model at a large enough distance from the central star, for water ice to be a major component. We assume the accreted material to be a mixture of silicate rock and ice, with no H-He envelope, as the accretion timescale is much longer than the time required for the nebular gas to dissipate. We adopt a thermal evolution model that includes accretional heating, radioactive energy release, and separation of ice and rock. Taking the Safronov parameter and the ice-to-rock ratio as free parameters, we compute growth and evolutionary sequences for different parameter combinations, for 4.6 Gyr. We find the final structure to depend significantly on both parameters. Low initial ice to rock ratios and high accretion rates, each resulting in increased heating rate, lead to the formation of extended rocky cores, while the opposite conditions leave the composition almost unchanged and result in relatively low internal temperatures. When rocky cores form, the ice-rich outer mantles still contain rock mixed with the ice. We find that a considerable fraction of the ice evaporates upon accretion, depending on parameters, and assume it is lost, thus the final surface composition and bulk density of the planet do not necessarily reflect the protoplanetary disk composition.
