Birkeland Current Correction for Mercury's Core Field Characterization
Abstract
Analysis of magnetometer observations by MESSENGER yielded insight into the unique nature of Mercury's intrinsic magnetic field, characterized as a weak, offset axial dipole (OAD). Our understanding of the internally generated field is limited by contamination from external signals present in Mercury's active magnetospheric environment. The largest of these externally driven signals, unaccounted for in corrections based on empirical models, are the Birkeland currents. Quantifying and correcting for the Birkeland current signals are critical as the currents, 1) flow at mid to high latitudes where the lowest altitude magnetometer measurements were taken, and 2) close through the interior of the planet causing the Birkeland current signals to be strongest close to the planetary surface. We use an adaptation of the terrestrial magnetospheric MHD (magnetohydrodynamics) code, GAMERA (Grid Agnostic MHD for Extended Research Applications), to simulate the solar-wind magnetosphere interaction at Mercury including the Birkeland currents. Using an OAD planetary field and a pseudo-ionosphere placed at the approximate core-mantle boundary depth to achieve closure of the currents within the planet, we are able to quantify and map Birkeland current signals for various solar wind conditions. The simulation results are benchmarked against the magnetopause shape fit from recent studies. Comparisons of MESSENGER observations and the resulting magnetic fields from the simulation at high latitudes close to the planet is used to assess the improvement in quantifying external fields offered by the simulation over statistical field models. Ongoing work will correct for the Birkeland currents to improve characterization of small-scale structures in Mercury's internal field with amplitudes ~10% or less than that of the OAD field at the planetary surface, and thereby inform the science analysis for BepiColombo.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2020
- Bibcode:
- 2020AGUFMP078.0007A
- Keywords:
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- 6235 Mercury;
- PLANETARY SCIENCES: SOLAR SYSTEM OBJECTS;
- 5405 Atmospheres;
- PLANETARY SCIENCES: SOLID SURFACE PLANETS;
- 5430 Interiors;
- PLANETARY SCIENCES: SOLID SURFACE PLANETS;
- 5443 Magnetospheres;
- PLANETARY SCIENCES: SOLID SURFACE PLANETS