2025-04-15 ジョンズ・ホプキンス大学(JHU)
＜関連情報＞
- https://hub.jhu.edu/2025/04/15/mars-molten-core-magnetic-mystery/
- https://agupubs.onlinelibrary.wiley.com/doi/10.1029/2024GL113926
フルスフィアダイナモによる火星の半球磁場 Mars’ Hemispheric Magnetic Field From a Full-Sphere Dynamo
C. Yan, A. Barik, S. Stanley, A. Mittelholz, A.-C. Plesa, C.-L. Johnson
Geophysical Research Letters Published: 05 February 2025
DOI:https://doi.org/10.1029/2024GL113926
Abstract
Seismic measurements from the NASA Mars InSight mission revealed that Mars’ core has a relatively low density, implying a larger fraction of lighter elements than previously thought, which further leads to a low melting temperature. Thus, Mars probably never developed a solid inner core during its early history when the dynamo was active. We perform full-sphere dynamo simulations to eliminate the influence of an inner core on dynamo behaviors and investigate how various magnitudes of heat flux perturbations at the core-mantle boundary affect the field morphology, comparing results to those from models with small inner cores. We find that a hemispheric magnetic field can result when the heat flux is concentrated in one hemisphere. Moreover, a dynamo model without the presence of an inner core can better explain Mars’ crustal magnetic field dichotomy than that in a spherical shell surrounding a solid inner core.
Key Points
- We perform full-sphere numerical dynamo simulations to investigate the effects of thermal perturbations on the ancient martian dynamo
- We find hemispheric thermal perturbations at the core-mantle boundary lead to magnetic fields compatible with Mars’ crustal magnetic hemisphericity
- Full-sphere dynamo models produce more hemispheric magnetic fields than dynamo models in spherical shells
Plain Language Summary
Recent measurements from the NASA Mars InSight mission show that Mars’ core is less dense than we previously believed. This indicates that Mars probably never developed a solid inner core in the earliest times in its history. Here we conducted simulations to understand the effects of this lack of a solid inner core. We find that the lack of an inner core can better explain the north-south dichotomy of Mars’ observed magnetic field.
