How well do present data constrain Ganymede's core magnetic field?

Ganymede is the only moon in our solar system known to have a large-scale intrinsic magnetic field, likely generated in the moon's metallic core. Initial analyses of Galileo spacecraft measurements concluded that Ganymede's intrinsic magnetic field is dominated by a magnetic dipole and that quadrupolar contributions are exceptionally weak. These findings have influenced the development of models for Ganymede's core dynamo over the past two decades. Recent magnetic data collected by the Juno spacecraft near Ganymede confirmed the original findings. Here, we reassess Ganymede's internal field contributions based on the magnetic measurements from close Galileo flybys of Ganymede (G1, G2, G7, G8, G28, G29), adding the recent Juno flyby. We use the same approach as previous studies but extend our analysis to higher spherical harmonic degrees to assess the range of magnetic field spherical harmonic models that fit the data. Our choice of spherical harmonic degrees is justified using a coefficient correlation analysis. We find that the limited spatial coverage of available Ganymede magnetic data precludes conclusions regarding quadrupolar strength, as we are able to construct spherical harmonic models for any source radius within Ganymede's range of likely core radii. Contributions from induced fields in Ganymede's oceans do not change our conclusions.