Interior-atmosphere feedbacks and the nature of detected sub-Neptunian planets

太阳系外行星这个相对年轻的研究领域已经揭示了行星出乎意料的巨大多样性，这是太阳系研究无法预见的。热木星是不能在观测到的地方形成的，这一惊人的发现改变了我们对行星形成和演化的理解。热木星并没有被明确划分为岩石行星和气体行星。在亚海王星质量和半径区域（M<20M_Earth和R<4R_Earth）中发现了岩石行星和气态行星之间相当连续的转变，并通过对行星半径和质量的独立测量进行了识别。在这种状态下，行星的平均密度可以用各种内部结构来解释，这些结构基于铁核、岩石地幔、可能的冰层和或多或少厚的大气层，所有这些结构的比例都很难限制。这些行星的大气层可能有不同的起源，如原行星盘的吸积，被吸积冰的升华，或从内部放出气体。在这个项目中，我们的目标是了解在亚海王星质量半径范围内被探测到的行星，由于地幔融化和火山作用，从岩石内部次生出气在原则上是可能的。此外，我们感兴趣的是了解由于放空和随后的大气条件变化和逃逸引起的大气内部反馈对测量的行星半径的影响有多大。我们将扩展内部结构、热演化和排气演化模型以及大气模型，并将其应用于亚海王星质量半径范围内的观测行星。推断出的内部结构将为研究内部热演化和潜在的脱气以及大气温度和成分建立起点。我们预计，从内部放出的气体，特别是二氧化碳，可能会导致大气质量、成分以及大气温度的重大变化。与合作伙伴一起，我们将探索这些模拟的大气是否会受到强烈的大气逸出的影响，以及在何种情况下，二氧化碳排放可能会改变损失过程。最后通过建立一个耦合的内部-大气模型来考虑大气温度和质量对内部演化的反馈。这些关于行星内部和大气的详细模型计算结果将与内部结构模拟的初步结果进行比较，以表明在哪些条件下这些过程可能实质性地改变行星的表观半径。这可能使我们能够排除仅从内部结构模型得出的某些解，并对所研究物体的性质施加额外的限制。

The relatively young research field of extrasolar planets has revealed an unexpectedly large diversity of planets, which could not be foreseen from studies of the Solar System. After the astonishing discovery of Hot Jupiters, which can not be formed where they are observed, the finding that no clear division into rocky and gaseous planets is realized, has revolutionized our understanding of planetary formation and evolution. The rather continuous transition between rocky and gaseous planets is found in the sub-Neptunian mass and radius regime (M<20M_Earth and R<4R_Earth), and was identified by independent measurements of planetary radius and mass. The resulting mean density of planets in these regime can be accounted for in terms of a variety of interior structures based on an iron core, a rocky mantle, possibly an ice layer, and a more or less thick atmosphere, all of them in proportions that are difficult to constrain. The atmospheres of these planets may have different origins, such as accretion from the protoplanetary disc, sublimation of accreted ices, or outgassing from the interior. In this project, we aim at understanding for which detected planets in the sub-Neptunian mass-radius regime secondary outgassing from rocky interiors due to mantle melting and volcanism is in principle possible. Furthermore, we are interested in understanding how large the impact of interior-atmosphere feedbacks due to the outgassing and subsequent changes in the atmospheric conditions and escape may be on the measured planetary radius. We will expand models of interior structure, thermal and outgassing evolution, as well as atmosphere models and apply them to observed planets in the sub-Neptunian mass-radius regime. The inferred interior structures will build the starting point of investigations of the interior thermal evolution and potential outgassing, as well as of the atmospheric temperature and composition. We expect that outgassing from the interior, of CO2 in particular, may lead to important changes in the atmospheric mass, composition and, in turn, also atmospheric temperatures. Together with collaboration partners, we will explore whether these modeled atmospheres are subject to strong atmospheric escape, and under which circumstances CO2-outgassing may alter the loss processes. The feedback of the atmospheric temperature and mass upon the interior evolution will be finally considered by building a coupled interior-atmosphere model.The results of these detailed model calculations of the planetary interior and atmosphere will be compared to the initial results of the interior structure modelling to show under which conditions these processes may substantially modify the apparent planetary radius. This may allow us to rule out certain solutions derived from interior structure models alone and to put additional constraints on the nature of the investigated bodies.