Melting, impacts, and the volatile contents of the interiors and atmospheres of Mars and Venus

自行星形成以来，行星地幔的融化过程在许多方面影响着行星的成分演化。融化的最重要的后果之一是地幔挥发性微量成分的动员和重新分配，特别是水和二氧化碳，在地幔内部，在地幔和地壳之间，最终也在内部和大气之间，因为挥发性物质在火山活动期间被释放出来。因此，融化不仅影响内部的化学状态，而且对大气的形成和随后的气候演变也起着至关重要的作用。然而，大气也通过表面压力控制脱气效率，对内部施加反馈影响。陨石撞击是行星早期演化的主要地质影响。各种类型和大小的撞击物都在不同程度上侵蚀和补充了目标行星的大气，较大的撞击物能够深入固体行星并引发地球动力学过程；再一次，融化是其中最重要的一个。因此，在一般的融化过程、陨石撞击和大气之间存在着复杂的相互作用，这可能使行星走上截然不同的进化道路。在提出的项目中，这些相互作用将借助地幔对流、撞击动力学和大气演化的数值模型来研究，这些模型将以不同的方式耦合；处理这些任务的算法要么已经存在，并将被调整和改进，要么将为此目的而开发。地幔对流形成了演化模式的长期框架，并被冲击打断，这些冲击表现为瞬时扰动；大气模型作为地幔模型的边界条件，然而，地幔模型不是静态的，而是可以以自己的方式演变，并与地幔和撞击相互作用。这个复合模型将专门用于模拟火星和金星的演化，这两个太阳系中的类地天体在许多方面与地球最相似。除其他事项外，它将用于限制其地幔中水和二氧化碳的初始浓度及其再分配，尝试与观测结果进行比较，并考虑从内部长期损失挥发物的动力学后果，例如，关于形成一个停滞的盖子。大气模块将用于阐明排气和气候之间的反馈机制，特别是在像金星那样升级到高压、高温温室条件的情况下。撞击模块将测试撞击如何决定性地调节内部和大气的化学演变，以及它们的净效应是消耗还是滋养大气。

Melting processes in planetary mantles have been shaping the compositional evolution of planets since their time of formation in many respects. One of the most important consequences of melting is the mobilization and redistribution of volatile trace components of the mantle, in particular water and carbon dioxide, within the mantle, between mantle and crust, and ultimately also between the interior and the atmosphere, as volatiles are outgassed during volcanic activity. Melting therefore influences not only the chemical state of the interior but plays also a crucial role in the build-up of an atmosphere and the subsequent climate evolution. The atmosphere, however, also exerts a feedback influence on the interior by controlling the efficiency of degassing via the pressure at the surface.Meteorite impacts were a major geological influence in the early evolution of the planets. Impactors of all types and sizes have both eroded and replenished the atmospheres of their target planets to different extents, and the larger ones were able to penetrate deeper into the solid planet and trigger geodynamical processes; again, melting is one of the most important of them. There is, then, a complex interplay between melting processes in general, meteorite impacts, and the atmosphere, which may put planets on quite different evolutionary paths.In the proposed project, these interactions will be studied with the help of numerical models of mantle convection, of impact dynamics, and of atmospheric evolution, which will be coupled in different ways; the algorithms that handle these tasks either exist already and will be adapted and refined or they will be developed for the purpose. The mantle convection forms the long-term framework of the evolution model and is punctuated by impacts, which appear as instantaneous perturbations; the atmosphere model acts as a boundary condition for the mantle model that is, however, not static but can evolve in its own way and in interaction with the mantle and the impacts.This composite model will be used specifically to model the evolutions of Mars and Venus, the two terrestrial bodies in our Solar System that are in many respects most similar to Earth. Among other things, it will be used to constrain the initial concentrations of water and carbon dioxide in their mantles and their redistribution, attempt a comparison with observations, and consider the dynamical consequences of the secular loss of volatiles from the interior, e.g., with regard to the formation of a stagnant lid. The atmosphere module will be used to elucidate the feedback mechanisms between outgassing and climate, in particular in cases like the escalation into high-pressure, high-temperature greenhouse conditions as on Venus. The impact module will test how decisively impacts modulated the chemical evolution of the interior and the atmosphere and whether their net effect was to deplete or feed the atmosphere.