Numerical simulations of the thermo-chemical evolution of the cores of Ganymede and Europa and implications for magnetic field generation in terrestrial planets

伽利略任务中最引人注目的发现之一是在木星的卫星木卫三上探测到了一个自我维持的磁场。在本项目中，将使用参数化对流、驱动发电机的核心过程的热力学描述以及具有铁降雪和铁-硫化物浮选的核心的发电机模型来模拟木卫三的热化学演化和磁场历史。目的是了解核心成分和地幔流变学等参数如何限制核心对流(热或组成)和核心中的发电机活动，并提出对木卫三磁场的解释。同时，我们需要提供一个解释，为什么木卫二上缺少一个领域。最近关于Fe-FeS系统的实验数据表明，木卫三中的发电机可能是由成分驱动的，但它的功能可能与地球发电机有很大不同。在后一种情况下，内核从下方生长，驱动内核和发电机中的对流。在木卫三(和木卫二)，核心可能通过降水和铁雪的降落和/或通过FeS薄片的漂浮而冻结。在足够小的行星和卫星中，这可能发生在距离共晶成分足够近的核心中。我们将讨论该模型在火星等其他行星上的应用。

One of the most compelling discoveries of the Galileo mission was the detection of a selfsustained magnetic field at Jupiter’s moon Ganymede. In the present project, the thermochemical evolution and the magnetic field history of Ganymede will be modelled using parameterized convection, a thermodynamic description of core processes driving the dynamo, and dynamo models of cores with iron snowfall and iron-sulfide flotation. The aim is to understand how parameters such as core composition and mantle rheology would constrain core convection (thermal or compositional) and dynamo action in the core and to come up with an explanation for the magnetic field of Ganymede. At the same time we need to provide an explanation why a field is lacking on Europa. Recent experimental data on the Fe-FeS system suggest that the dynamo in Ganymede may be compositionally driven but that it may function substantially different than the geodynamo. In the latter, an inner core grows from below driving convection in the core and the dynamo. In Ganymede (and in Europa) the core may freeze via precipitation and the fall of Fe snow and/or through the floating of FeS flakes. This may occur in cores sufficiently close to the eutectic composition in sufficiently small planets and satellites. We will discuss the application of the model to other planets such as Mars.