Exploring the causes of exoplanetary atmospheric evaporation

系外行星宜居性的关键决定因素之一是其大气条件。因此，了解系外行星形成后及其演化过程中可能影响它们的质量损失机制就变得非常重要。这项工作将是开发这种机制的模型。研究小组将对现有的模型进行调整，使其适用于三颗围绕类似恒星运行的类似凌日行星。三颗行星中的两颗在凌日时显示出大气蒸发的证据，但第三颗行星没有。这三个世界如此相似，但大气蒸发的结果却如此不同，这可能为研究行星演化提供了独特的视角。这项工作将支持一名研究生和四名女本科生实习生。实习的部分内容将包括参加一个关于科学传播的讲习班。PI还将通过参加在南非的达特茅斯外国研究项目开展外联活动。该团队将调整蒸发系外行星代码（EVE），包括三种尚未纳入代码的新现象。他们将使用代码生成围绕三颗类似恒星运行的三颗类似系外行星的模型：K2-25b、Gl 436b和GJ 3470b。其中，K2-25b没有观测到有大气蒸发现象，但另外两颗有。一旦了解了这些系统，研究小组将进行一项参数研究，以评估行星外行星层是如何受到恒星和行星参数范围内的影响的。特别是，该团队将探索基于粒子的模型与流体力学代码的有效性，以解决完整的3D恒星风问题。它们还将包括由行星外逸层和恒星风之间的电荷交换产生的拾取质子。先前的模型忽略了这种潜在的粒子来源。他们还将明确地模拟大气中的氦，这在以前的模型中没有包括在内。该奖项反映了美国国家科学基金会的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

One of the key determining factors for exoplanet habitability is the condition of its atmosphere. It then becomes important to understand the mass loss mechanisms that might affect exoplanets after their formation and through their evolution. This work will be to develop models of this mechanism. The team will adapt an existing model to three similar transiting planets which orbit similar stars. Two of the three planets show evidence of atmospheric evaporation in their transits, but the third planet does not. These three worlds, so similar but yet with such different results for atmospheric evaporation, might provide a unique insight into planetary evolution. This work will support a graduate student and will support four female undergraduate interns. Part of the internships will include participation in a workshop on science communication. The PI will also conduct outreach by participating in the Dartmouth Foreign Studies Program in South Africa.The team will adapt the Evaporating Exoplanet code (EVE) by including three new phenomena that have not yet been incorporated into the code. They will use the code to produce models of three similar exoplanets around three similar stars: K2-25b, Gl 436b, and GJ 3470b. Of these, K2-25b has not been observed to exhibit atmospheric evaporation, but the other two have. Once these systems have been understood, the team will conduct a parameter study to assess how planetary exospheres are impacted by their stars across a range of stellar and planetary parameters. In particular, the team will explore the efficacy of particle-based models versus hydrodynamic codes for the full 3D stellar wind problem. They will also include pickup protons which result from charge exchange between the planetary exosphere and the stellar wind. Prior models neglected this potential source of particles. They will also explicitly model atmospheric helium, which has not been included in prior models.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.