Can the magnetic field induced by convective flow constrain the properties of Ganymede's subsurface ocean?

TL;DR

This study evaluates the magnetic field generated by Ganymede's subsurface ocean, demonstrating its potential to reveal ocean properties and flow regimes through magnetic measurements.

Contribution

It introduces a simplified electromagnetic induction model to assess the ocean-induced magnetic field and its use in constraining Ganymede's internal structure.

Findings

OIMF is a measurable stationary signal of a few nT amplitude.

OIMF pattern shifts with ocean thickness, aiding in constraining ocean depth.

Stationary OIMF primarily driven by toroidal flow component.

Abstract

This paper has two main objectives. First, we assess the strength and measurability of Ganymede's ocean-induced magnetic field (OIMF) generated by the flow in the subsurface ocean. Second, we inspect how the OIMF constrains the ocean flow and Ganymede's internal structure and suggest a suitable metric for this purpose. We calculate the OIMF by solving the electromagnetic induction (EMI) equation in the simplified form, where we neglect the ocean-induced field in the advection term and the motionless induction. We show that this approach is sufficiently accurate by comparison with the solution of the full EMI equation. We also demonstrate that the OIMF is predominantly a stationary signal generated by the interaction of the toroidal component of the flow with Ganymede's internal field. The contributions to the OIMF due to the poloidal component of the flow and Jupiter's magnetic field can be neglected as second-order effects. The stationary OIMF is a measurable quantity with a few nT amplitude on Ganymede's surface if the ocean is sufficiently thick (approximately 400 km) and conductive (approximately 5 S/m). In this case, the specific footprint of the measured OIMF could be used to identify the flow regime (mode) of the convecting ocean. Additionally, the OIMF can be used to determine the ocean thickness since the OIMF pattern is shifted towards low latitudes if the ocean thickness is reduced.