TRAPPIST-1行星上的彗星撞击物可以摧毁所有的行星大气，并在行星f、g、h上重建次级大气
Cometary impactors on the TRAPPIST-1 planets can destroy all planetary atmospheres and rebuild secondary atmospheres on planets f, g, h
摘要：
TRAPPIST-1系统的独特之处在于它有一个由七颗类地行星组成的链条，这些行星位于其宜居带附近或之中。在本文中，我们研究了潜在的彗星撞击对TRAPPIST-1行星的影响，以及它们将如何影响这些行星的原始大气。我们考虑了大气质量损失和挥发性物质的释放，以评估任何种类的生命是否有机会发展。我们运行了N体模拟来研究潜在撞击彗星的轨道演化，以确定哪些行星更有可能被撞击以及撞击速度的分布。我们考虑了三种可能将彗星从类似于柯伊伯带或奥尔特云的外带（尚未被发现）抛入内区（即七颗行星所在的0.1au范围内）的情况：行星散射，Kozai-Lidov机制和银河潮汐。对于不同的场景，我们量化了每个行星的大气质量损失以及在系统的年龄内可以传递的挥发物质量，这取决于从外部带散射出来的质量。我们发现，由此产生的高速撞击可以很容易地破坏所有七颗行星的原始大气，即使从外层带散射的质量与柯伊伯带一样低。然而，我们发现最外层的行星f、g和h的大气层也可以很容易地被彗星挥发物补充（例如$\sim$，地球海洋质量的水可以被输送）。因此，这些情况意味着这些最外层行星的大气层可能比最内层行星的大气层更大，并且具有富含挥发物的成分。
英文摘要：
The TRAPPIST-1 system is unique in that it has a chain of seven terrestrial Earth-like planets located close to or in its habitable zone. In this paper, we study the effect of potential cometary impacts on the TRAPPIST-1 planets and how they would affect the primordial atmospheres of these planets. We consider both atmospheric mass loss and volatile delivery with a view to assessing whether any sort of life has a chance to develop. We ran N-body simulations to investigate the orbital evolution of potential impacting comets, to determine which planets are more likely to be impacted and the distributions of impact velocities. We consider three scenarios that could potentially throw comets into the inner region (i.e within 0.1au where the seven planets are located) from an (as yet undetected) outer belt similar to the Kuiper belt or an Oort cloud: Planet scattering, the Kozai-Lidov mechanism and Galactic tides. For the different scenarios, we quantify, for each planet, how much atmospheric mass is lost and what mass of volatiles can be delivered over the age of the system depending on the mass scattered out of the outer belt. We find that the resulting high velocity impacts can easily destroy the primordial atmospheres of all seven planets, even if the mass scattered from the outer belt is as low as that of the Kuiper belt. However, we find that the atmospheres of the outermost planets f, g and h can also easily be replenished with cometary volatiles (e.g. $\sim$ an Earth ocean mass of water could be delivered). These scenarios would thus imply that the atmospheres of these outermost planets could be more massive than those of the innermost planets, and have volatiles-enriched composition.
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