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FLUDYCO Report Summary

Project ID: 681835
Funded under: H2020-EU.1.1.

Periodic Reporting for period 1 - FLUDYCO (Fluid dynamics of planetary cores: formation, heterogeneous convection and rotational dynamics)

Reporting period: 2016-07-01 to 2017-12-31

Summary of the context and overall objectives of the project

Understanding the flows in planetary cores from their formation to their current dynamics is a tremendous interdisciplinary challenge. Beyond the challenge in fundamental fluid dynamics to understand these extraordinary flows involving turbulence, rotation and buoyancy at typical scales well beyond our day-to-day experience, a global knowledge of the involved processes is fundamental to a better understanding of the initial state of planets, of their thermal and orbital evolution, and of magnetic field generation, all key ingredients for habitability.

The purpose of the present project is to go beyond the state-of-the-art in tackling three barriers at the current frontier of knowledge. It combines groundbreaking laboratory experiments, complementary pioneering numerical simulations, and fruitful collaborations with leaders in various fields of planetary sciences. Improving on the latest advances in the field, we address the fluid dynamics of iron fragmentation during the later stages of planetary accretion, in order to produce innovative, dynamically reliable models of planet formation. Considering the latest published data for Earth, we investigate the flows driven in a stratified layer at the top of a liquid core and their influence on the global convective dynamics and related dynamo. Finally, building upon the recent emergence of alternative models for core dynamics, we quantitatively examine the non-linear saturation and turbulent state of the flows driven by libration, as well as the shape and intensity of the corresponding dynamo.

In the context of an international competition, the originality of this work comes from its multi-method and interdisciplinary character.

Work performed from the beginning of the project to the end of the period covered by the report and main results achieved so far

Our research activity during these first 18 months has led to the publication of 7 articles (plus 2 submitted) in top-level journals, with significant contributions in the 3 scientific tasks described in the DoA. Major achievements include:
• Task 1 - core formation: the first description and quantification of the turbulent exchanges taking place during core formation using innovative laboratory experiments, that have been awarded the Gallery of Fluid Motion video prize at the American Physical Society, Division of Fluid dynamics congress in 2016 (Wacheul & Le Bars PRF 2017).
• Task 2 - core convection: the first demonstration of the emergence of a long-term, large-scale, oscillating flow in a stratified layer adjacent to a turbulent one, generalizing the concept of QBO to planetary cores (Couston et al 2018, submitted).
• Task 3 - core rotation: the first numerical realization of an inertial wave turbulence (Le Reun et al. PRL 2017), which fundamentally changes our view of core rotating turbulence. This work has played a large role in the awarding to B. Favier of the Young Scientist Award of the European Turbulence Conference 2017 (Stockholm, August 21-24).
All team members have significantly taken part to the dissemination of our results towards scientific communities ranging from fluid mechanics to planetology (participation to and organization of conferences, publications), as well as towards a larger public (setting of a website, participation to the "Fête de la Science", press release and journal articles).

Progress beyond the state of the art and expected potential impact (including the socio-economic impact and the wider societal implications of the project so far)

Our activities combining laboratory experiments and numerical simulations will be pursued on the three tasks, following and extending the first results obtained. Additionally, during the next period, efforts will be put on
• Task 1 - core formation: the development of new numerical simulations quantifying the shape dynamics and the thermochemical exchanges at the scale of one drop.
• Task 2 - core convection: the systematic experimental study of the convection in a two-domain system (water around 4oC) and the setting of a new experimental set-up, dedicated to the study of the interaction between turbulence and a stably stratified layer in fast rotation.
• Task 3 - core rotation: the systematic numerical study of the dynamo driven by libration in planetary cores, and more generally by any mechanical forcing.
All team members will keep taking part to the dissemination of our results towards scientific communities as well as towards a larger public. Specifically, a one-week summer school will be organized in Udine (Italy) and 4 outreach movies will be realized to explain our research activities.

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