Atmospheric mass loss due to giant impacts: the importance of the thermal component for hydrogen-helium envelopes.
Atmospheric mass loss due to giant impacts: the importance of the thermal component for hydrogen-helium envelopes.
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巨大撞击造成的大气质量损失：热成分对于氢氦包层的重要性。
DOI：
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发表时间：
2018
影响因子：
4.8
通讯作者：
H. Schlichting
中科院分区：
文献类型：
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作者：
J. Biersteker;H. Schlichting
近距离的超级地球和小海王星系统在行星的体积密度和组成上显示出惊人的多样性。巨大的撞击预计将在许多这样的世界的形成中发挥作用。以前的工作集中在巨大撞击造成的机械冲击上，表明这些撞击可以弹出行星包层的很大一部分，为观测到的系外行星成分的扩散提供了部分解释。在这里，我们研究了巨大碰撞的热后果，并表明这些影响造成的大气损失可以显著超过氢-氦(H/He)包层的机械冲击造成的损失。具体地说，当发生巨大的撞击时，部分撞击能被转化为热能，加热岩石核心和包体。我们发现，包层随后的热膨胀可以通过帕克风导致一段持续、快速的质量损失，导致H/He包层的部分或全部侵蚀。包层质量损失的比例取决于行星到其主星的轨道距离和它的初始热状态，因此也取决于年龄。与轨道较宽的行星相比，距离其主星较近的行星更容易受到撞击引发的热大气损失的影响。同样，较年轻的行星，其岩石核心仍然很热，在形成过程中仍处于熔融状态，遭受更大的大气损失。这一点特别有趣，因为巨大的撞击预计将在形成后10-100英里发生，而此时超级地球仍然保留着来自形成的大量内部热量。对于核心热能远大于包层能量的行星，即H/He包层质量分数大致小于8%的超地球，显著消除大气所需的撞击器质量为M imp/MP~μ/μc~0.1，大致相当于包层和核的热容之比。相反，当包络能量主导总能量收支时，当冲击器质量与包络质量相当时，可能会发生完全损失。
Systems of close-in super-Earths and mini-Neptunes display striking diversity in planetary bulk density and composition. Giant impacts are expected to play a role in the formation of many of these worlds. Previous works, focused on the mechanical shock caused by a giant impact, have shown that these impacts can eject large fractions of the planetary envelope, offering a partial explanation for the observed spread in exoplanet compositions. Here, we examine the thermal consequences of giant impacts, and show that the atmospheric loss caused by these effects can significantly exceed that caused by mechanical shocks for hydrogen-helium (H/He) envelopes. Specifically, when a giant impact occurs, part of the impact energy is converted into thermal energy, heating the rocky core and the envelope. We find that the ensuing thermal expansion of the envelope can lead to a period of sustained, rapid mass loss through a Parker wind, resulting in the partial or complete erosion of the H/He envelope. The fraction of the envelope mass lost depends on the planet's orbital distance from its host star and its initial thermal state, and hence age. Planets closer to their host stars are more susceptible to thermal atmospheric loss triggered by impacts than ones on wider orbits. Similarly, younger planets, with rocky cores which are still hot and molten from formation, suffer greater atmospheric loss. This is especially interesting because giant impacts are expected to occur 10-100 Myr after formation, at a time when super-Earths still retain significant internal heat from formation. For planets where the thermal energy of the core is much greater than the envelope energy, i.e. super-Earths with H/He envelope mass fractions roughly less than 8 per cent, the impactor mass required for significant atmospheric removal is M imp/Mp ~ μ/μc ~ 0.1, approximately the ratio of the heat capacities of the envelope and core. In contrast, when the envelope energy dominates the total energy budget, complete loss can occur when the impactor mass is comparable to the envelope mass.
隐藏的行星朋友：在有一个遥远的、倾斜的伴星存在的情况下，关于两行星系统的稳定性
影响因子：
4.8
作者：
Denham, Paul;Naoz, Smadar;Hoang, Bao-Minh;Stephan, Alexander P;Farr, Will M
通讯作者：
Farr, Will M