The Grüneisen parameter of iron under extreme conditions and its influence on thermal convection in super-earth cores

We combined recent experimental data with analytical models to investigate the evolution of the Grüneisen parameter (γ) for iron under conditions relevant to the cores of rocky planets ranging from 1 to 5 Earth masses. γ relates thermal and elastic properties of materials and is a critical factor for understanding the dynamic behavior of planetary interiors. Previous sound speed measurements of the iron γ at Earth's core conditions, combined with seismic velocity data, significantly enhanced our understanding of the planet's interior [1]. Extending these studies to extreme conditions of larger planets can thus offer new insights into their internal properties. Recent laser-driven shock experiments measured γ for both liquid and solid iron at pressures of up to 3 TPa [2, 3]. By fitting this expanded dataset with the Altshuler and Anderson formalisms [4], we derived updated γ values that allowed us to assess temperature profiles for a range of planetary core sizes. These preliminary findings enabled us to assess the efficiency of thermal convection in super-Earth cores, providing valuable insights into their dynamic behavior.

 

References:

[1] Antonangeli & Ohtani. Progress in Earth and Planetary Science 2 (2015): 1-11.

[2] Huff et al. (2024) Phys. Rev. B, 109.18,184311.

[3] Smith et al. (2018) Nat. Astr., 2.6, 452.

[4] Clesi & Deguen (2024) GJI, 237 (3), 1275.