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Thesis Format

Integrated Article

Degree

Master of Science

Program

Geophysics

Supervisor

Secco, Richard A.

2nd Supervisor

Yong, Wenjun

Co-Supervisor

Abstract

Insights from high pressure and temperature experiments involving in-situ measurements of the electrical resistivity of Fe-5wt%Ni at temperatures of up to 2000 K, under pressures of 2-5 GPa in a 1000-ton cubic-anvil press have been used to reveal Vesta’s core dynamics. The Wiedemann–Franz law was used to calculate the thermal conductivity from the measured electrical resistivity data. Comparing the findings of this study with prior investigations on both pure Fe and Fe-10wt%Ni indicates that an increase in Ni ranging from 0-10wt% has negligible effect on the electrical resistivity of Fe alloys. By comparing the range of estimated heat flux through the core-mantle boundary of 1.5–78 GW to the estimated adiabatic core heat flux ~331 MW at the top of Vesta’s core determined in this study, we conclude that the mechanism behind Vesta’s past core dynamo that generated its surface magnetic field during its early history was thermal convection.

Summary for Lay Audience

This study explored the inner workings of Vesta, a differentiated planetary body with a metallic core, thought to have emerged during the early formation of our solar system, by conducting high pressure and temperature experiments on a potential core-mimetic alloy. By measuring the electrical resistivity of this alloy under extreme pressure and temperature conditions, we gained insights into Vesta’s past magnetic field activity. The Fe alloy, composed of 95wt% iron and 5wt% nickel (Fe5Ni), was subjected to temperatures of up to 2000 K, under pressures of 2-5 GPa in a 1000-ton cubic-anvil press, simulating the pressure and temperature conditions deep within Vesta. By measuring its electrical resistivity, its thermal conductivity was calculated which indicates how efficiently heat travels through the core's outer layer. Using thermal conductivity, the conducted heat flux within Vesta’s core was determined. Applying these findings to Vesta, the second-largest asteroid in our solar system, revealed that during its early history, Vesta likely experienced thermal convection within its core. This means that the liquid core underwent vigorous heat-driven motion. Such movement generates magnetic fields, similar to what we observe on Earth. The results of this study provide insight on Vesta's past magnetic field and contributes to our understanding of how small celestial bodies can generate magnetic fields through processes like thermal convection.

Creative Commons License

Creative Commons Attribution 4.0 License
This work is licensed under a Creative Commons Attribution 4.0 License.

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