Viscosity and thermal conductivity - from Earth's lower mantle to Super-Earth models

Abstract:

Numerical convection models are often used to investigate the interior thermal evolution of our Earth and other Earth-like planets. For this, detailed information is needed on how transport properties depend on rock assemblages for large temperature and pressure ranges. However, most available (theoretically or experimentally derived) data have been obtained for Earth's mantle, and often only for single minerals instead of rocks. Especially when studying the possible interior evolution of extra-solar planets with a potentially very different composition, reliable data on transport properties are missing. However, especially the importance of the viscosity on the mantle evolution has often been discussed in the literature. It has been suggested for example, that the lower part of the mantle of super-Earth planets might become more sluggish due to the high pressure effect on the viscosity and may need to heat up extensively to allow for mantle convection [1,2], with possible viscosity jumps depending on the mineral stability and diffusion mechanisms additionally affecting the strength of mantle convection [3,4].

The temperature evolution plays a major role for how a rocky mantle behaves at high pressures. The efficiency of mantle cooling (and hence core cooling) determines if a magnetic field can be induced and maintained. The strength of the convective behaviour in the mantle on the other hand influences the likelihood for the lithosphere to break into plates or to behave instead as a stagnant-lid planet such as Mars [5], and limits the strength of volcanic activity [6]. The thermal conductivity is therefore just as much a key player as the viscosity for the long-term thermal evolution of the deep interior of Earth and more generally super-Earths, since the transport of heat at pressures relevant for rocky mantles is dominated by conduction and convection.

References:

1. Karato, Shun-ichiro. Icarus 212.1 (2011): 14-23.
2. Stein, C., J. P. Lowman, and U. Hansen. Earth and Planetary Science Letters 361 (2013): 448-459.
3. Stamenkovic, V., L. Noack, D. Breuer, and T. Spohn. The Astrophysical Journal 748.1 (2012): 41.
4. Tackley, P.J., et al. Icarus 225.1 (2013): 50-61.
5. Noack, L. and D. Breuer. Planetary and Space Science 98 (2014): 41-49.
6. Dorn, C., L. Noack, and A. B. Rozel. Astronomy & Astrophysics 614 (2018): A18.