Unified Simulations of Planetary Formation and Atmospheric Evolution. II. Rapid Disk Clearing by Photoevaporation Yields Low-mass Super-Earth Atmospheres
Unified Simulations of Planetary Formation and Atmospheric Evolution. II. Rapid Disk Clearing by Photoevaporation Yields Low-mass Super-Earth Atmospheres
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DOI：
10.3847/1538-4357/aba75e
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发表时间：
2020-07
期刊：
影响因子：
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通讯作者：
M. Ogihara;M. Kunitomo;Y. Hori
中科院分区：
文献类型：
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作者：
M. Ogihara;M. Kunitomo;Y. Hori
超级地球拥有低质量的H2/He大气层(通常不到10%的质量)。然而，超级地球大气层的起源还没有被确定。我们研究了光蒸发快速清除圆盘在超级地球及其大气形成过程中的作用。我们在同时考虑光蒸发风和磁力驱动的盘风的情况下，对超级地球的形成和大气演化进行了统一的模拟。对于行星核的生长模式，我们考虑了行星胚胎在卵石吸积和无卵石吸积两种情况下的生长。我们的主要发现总结如下。(I)光蒸发导致的圆盘快速消散缩短了大气吸积的时间跨度，从而防止了超级地核吸积大质量大气。(Ii)即使在没有卵石吸积的情况下，行星核通过胚胎吸积而迅速生长，也会因为胚胎吸积的隔离质量较小而推迟了失控气体吸积的开始。再加上快速的磁盘清理，可以避免大质量大气的吸积。(Iii)在快速清除圆盘后，一些高偏心率胚胎可以保留在外轨道上。此后，这样的胚胎可能会与超级地球相撞，导致对吸积大气的有效撞击侵蚀。因此，我们发现，具有低质量H2/He大气的超级地球是由考虑真实圆盘演化的N体模拟自然产生的。
Super-Earths possess low-mass H2/He atmospheres (typically less than 10% by mass). However, the origins of super-Earth atmospheres have not yet been ascertained. We investigate the role of rapid disk clearing by photoevaporation during the formation of super-Earths and their atmospheres. We perform unified simulations of super-Earth formation and atmospheric evolution in evolving disks that consider both photoevaporative winds and magnetically driven disk winds. For the growth mode of planetary cores, we consider two cases in which planetary embryos grow with and without pebble accretion. Our main findings are summarized as follows. (i) The time span of atmospheric accretion is shortened by rapid disk dissipation due to photoevaporation, which prevents super-Earth cores from accreting massive atmospheres. (ii) Even if planetary cores grow rapidly by embryo accretion in the case without pebble accretion, the onset of runaway gas accretion is delayed because the isolation mass for embryo accretion is small. Together with rapid disk clearing, the accretion of massive atmospheres can be avoided. (iii) After rapid disk clearing, a number of high-eccentricity embryos can remain in outer orbits. Thereafter, such embryos may collide with the super-Earths, leading to efficient impact erosion of accreted atmospheres. Therefore, we find that super-Earths with low-mass H2/He atmospheres are naturally produced by N-body simulations that consider realistic disk evolution.