Impact-induced core heating has only short-term effects of planetary evolution

Recent impact simulations show that a planet’s iron core can be greatly heated by a giant impact – indeed , by more than the mantle above it (Zhou et al., 2024). This has been proposed to result in long-term influences on mantle evolution in Venus (Marchi et al., 2023), although previous works have shown that for an Earth-like planet, cases with different initial core temperature tend to converge to the same evolutionary path (Nakagawa and Tackley, 2010). Here, the evolution of the coupled mantle and core after giant impact heating of the core is examined using a 2D mantle model coupled to a 1D core model using the StagYY modelling framework.

If the outer core becomes hotter than the liquidus of mantle rock then it 100% melts the bottom of the mantle, with the molten mantle at the same potential temperature as the outer core. The melt front propagates rapidly upwards due to heat supplied by vigorous outer core & molten mantle convection (a Stefan problem) at the same time cooling the outer core rapidly. This phase of rapid mantle melting + core cooling continues until the bottom of the mantle has cooled to the rheological transition (~40% melt fraction). Depending on the temperature, the resulting very hot material at the base of the mantle tends to rise quickly in the form of plumes, causing a pulse of magmatism at the surface (in addition to any magmatism caused by impact heating of the mantle). At the bottom, melt-solid segregation upwards or downwards may result in further complexities including an iron-rich somewhat molten silicate layer. In any case, results show that impact heating of the core leads to transient phenomena rather than long-term dynamical effects.

Marchi, S., Rufu, R. & Korenaga, J. Long-lived volcanic resurfacing of Venus driven by early collisions. Nat Astron 7, 1180–1187 (2023). https://doi.org/10.1038/s41550-023-02037-2

Nakagawa, T. and P. J. Tackley (2010) Influence of initial CMB temperature and other parameters on the thermal evolution of Earth's core resulting from thermo-chemical spherical mantle convection, Geochem. Geophys. Geosys. 11, Q06001, 16 pp., doi:10.1029/2010GC003031.

Zhou, Y., Driscoll, P.E., Zhang, M., Reinhardt, C., Meier, T. (2024) A Scaling Relation for Core Heating by Giant Impacts and Implications for Dynamo Onset, Journal of Geophysical Research: Planets2024, 129(5), e2023JE008163