The initial temporal evolution of a feedback dynamo for Mercury

TL;DR

This paper investigates a feedback dynamo model for Mercury's magnetic field, showing how magnetosphere feedback can lead to a weak, steady magnetic field consistent with observations.

Contribution

It introduces a feedback dynamo model incorporating magnetospheric effects, explaining the weak magnetic field of Mercury through a negative feedback mechanism.

Findings

Feedback quenches the magnetic field to 100-150 nT.

Two stationary solutions with weak and strong fields are identified.

Weak field solution is achievable under certain dynamo conditions.

Abstract

Various possibilities are currently under discussion to explain the observed weakness of the intrinsic magnetic field of planet Mercury. One of the possible dynamo scenarios is a dynamo with feedback from the magnetosphere. Due to its weak magnetic field Mercury exhibits a small magnetosphere whose subsolar magnetopause distance is only about 1.7 Hermean radii. We consider the magnetic field due to magnetopause currents in the dynamo region. Since the external field of magnetospheric origin is antiparallel to the dipole component of the dynamo field, a negative feedback results. For an alpha-omega-dynamo two stationary solutions of such a feedback dynamo emerge, one with a weak and the other with a strong magnetic field. The question, however, is how these solutions can be realized. To address this problem, we discuss various scenarios for a simple dynamo model and the conditions under which a steady weak magnetic field can be reached. We find that the feedback mechanism quenches the overall field to a low value of about 100 to 150 nT if the dynamo is not driven too strongly.