Formation and Evolution of Protoatmospheres
Formation and Evolution of Protoatmospheres
复制标题
DOI：
10.1007/s11214-016-0280-1
复制
发表时间：
2016-09
影响因子：
10.3
通讯作者：
H. Massol;K. Hamano;F. Tian;M. Ikoma;Y. Abe;E. Chassefière;A. Davaille;H. Genda;M. Güdel;Y. Hori;F. Leblanc;E. Marcq;P. Sarda;V. Shematovich;A. Stökl;H. Lammer
中科院分区：
文献类型：
--
作者：
H. Massol;K. Hamano;F. Tian;M. Ikoma;Y. Abe;E. Chassefière;A. Davaille;H. Genda;M. Güdel;Y. Hori;F. Leblanc;E. Marcq;P. Sarda;V. Shematovich;A. Stökl;H. Lammer
讨论了行星原大气层与原行星盘的关系。行星的初始大气层主要可以通过两种形成情景来联系。如果一个原行星的核心在气体盘内增加质量并增长，它可以从盘中捕获H2，He和其他气体。当盘的气体蒸发时，被H2/He气体包层包围的核心暴露在年轻宿主星星的高X射线和极紫外线通量以及恒星风中。这段时间可以被认为是大气逃逸的开始。结果表明，低质量的天体吸积较少的气体，因此取决于宿主恒星的辐射环境，在数千万或数亿年后可能会失去气体包层。巨大的核心可能永远不会摆脱它们捕获的氢包层，并在其整个生命周期中保持为亚海王星，海王星或气体巨星。类地行星可能由于热大气逃逸而失去了捕获的气体包层，或者在原行星星云消失后吸积，在岩浆海洋凝固过程中会产生灾难性的脱气蒸汽大气。这些蒸汽大气层主要由水和二氧化碳组成，在原行星吸积过程中被合并到其中。在宜居带形成的行星，在几百万年内固化。在这种情况下，被排出的蒸汽大气快速冷却，导致水的冷凝和液态海洋的形成。另一方面，如果行星在临界距离内形成，即使它们释放了大量的水，岩浆海洋也会持续更长时间。在这种情况下，蒸汽大气层可能会保持1亿年甚至更长时间。在缓慢的凝固过程中，流体动力学的大气逃逸将使这些行星干燥。
The origin and evolution of planetary protoatmospheres in relation to the protoplanetary disk is discussed. The initial atmospheres of planets can mainly be related via two formation scenarios. If a protoplanetary core accretes mass and grows inside the gas disk, it can capture H2, He and other gases from the disk. When the gas of the disk evaporates, the core that is surrounded by the H2/He gas envelope is exposed to the high X-ray and extreme ultraviolet flux and stellar wind of the young host star. This period can be considered as the onset of atmospheric escape. It is shown that lower mass bodies accrete less gas and depending on the host stars radiation environment can therefore lose the gaseous envelope after tens or hundreds of million years. Massive cores may never get rid of their captured hydrogen envelopes and remain as sub-Neptunes, Neptunes or gas giants for their whole life time. Terrestrial planets which may have lost the captured gas envelope by thermal atmospheric escape, or which accreted after the protoplanetary nebula vanished will produce catastrophically outgassed steam atmospheres during the magma ocean solidification process. These steam atmospheres consist mainly of water and CO2that was incorporated into the protoplanet during its accretion. Planets, which are formed in the habitable zone, solidify within several million years. In such cases the outgassed steam atmospheres cool fast, which leads to the condensation of water and the formation of liquid oceans. On the other hand, magma oceans are sustained for longer if planets form inside a critical distance, even if they outgassed a larger initial amount of water. In such cases the steam atmosphere could remain 100 million years or for even longer. Hydrodynamic atmospheric escape will then desiccate these planets during the slow solidification process.