A reassessment of the in situ formation of close-in super-Earths
A reassessment of the in situ formation of close-in super-Earths
复制标题
DOI：
10.1051/0004-6361/201525884
复制
发表时间：
2015-04
影响因子：
6.5
通讯作者：
M. Ogihara;A. Morbidelli;T. Guillot
中科院分区：
文献类型：
--
作者：
M. Ogihara;A. Morbidelli;T. Guillot
上下文。很大一部分恒星拥有一个或多个近距离的超级地球行星。关于这些行星是在原地形成的，还是在离中心恒星更远的地方形成的，然后迁移到现在的位置，人们争论不休。已经证明，它们的部分观测性质（例如偏心分布）可以通过n -体模拟原位形成，从高质量原行星群体开始，忽略盘状气体的影响。目标。我们计划通过更完整的模拟来重新评估近地超级地球的原位形成。方法。我们对一群小型行星胚胎和星子进行了n体模拟，其中包括盘-行星相互作用的影响（例如，偏心阻尼，I型迁移）。此外，我们也考虑原始大气从原行星盘的吸积。结果。我们发现，在气体扩散之前，行星胚胎生长得非常快，因此经历了快速的向内迁移，这意味着在考虑近地超级地球的原位形成时，不能忽视气体盘的影响。由于它们的快速向内迁移，超级地球在靠近圆盘内缘的地方达到了一个紧凑的结构，其轨道参数的分布与观测到的近距离超级地球种群的分布非常不匹配。另一方面，包含偏心阻尼但不含I型偏移的模拟可以更好地再现观测到的分布。包括大气的吸积无助于重现观测的总体结构。有趣的是，我们发现大质量的胚胎可以在只捕获中等质量的氢/氦大气的情况下在圆盘边缘内迁移。通过这个过程，它们避免成为巨行星。结论。大部分靠近的超级地球不能原地形成，除非I型迁移在1au内的整个圆盘中被抑制。
Context. A large fraction of stars host one or multiple close-in super-Earth planets. There is an active debate about whether these planets formed in situ or at greater distances from the central star and migrated to their current position. It has been shown that part of their observed properties (e.g., eccentricity distribution) can be reproduced by N-body simulations of in situ formation starting with a population of protoplanets of high masses and neglecting the e ects of the disk gas. Aims. We plan to reassess the in situ formation of close-in super-Earths through more complete simulations. Methods. We performed N-body simulations of a population of small planetary embryos and planetesimals that include the e ects of disk-planet interactions (e.g., eccentricity damping, Type I migration). In addition, we also consider the accretion of a primitive atmosphere from a protoplanetary disk. Results. We find that planetary embryos grow very quickly well before the gas dispersal, and thus undergo rapid inward migration, which means that one cannot neglect the e ects of a gas disk when considering the in-situ formation of close-in super-Earths. Owing to their rapid inward migration, super-Earths reach a compact configuration near the disk’s inner edge whose distribution of orbital parameters matches the observed close-in super-Earths population poorly. On the other hand, simulations including eccentricity damping, but no Type I migration, reproduce the observed distributions better. Including the accretion of an atmosphere does not help reproduce the bulk architecture of observations. Interestingly, we find that the massive embryos can migrate inside the disk edge while capturing only a moderately massive hydrogen/helium atmosphere. By this process they avoid becoming giant planets. Conclusions. The bulk of close-in super-Earths cannot form in situ, unless Type I migration is suppressed in the entire disk inside 1 AU.