The Evolving Understanding of Saturn's Internal Magnetic Field: Insights from Pioneer 11 to Cassini

Pioneer 11 spacecraft in 1979 revealed that Saturn's internal magnetic field in 1979, it revealed that the magnetic field was three to five times weaker than anticipated. The magnetic field had a high degree of symmetry around its rotation axis, polarity opposite to that of the Earth's, and a slight northward dipole displacement of approximately 0.04 Rs. Subsequent observations by Voyagers 1 and 2, at more diverse latitudes in both hemispheres, corroborated and refined these findings. Voyager 2 indicated a steady, smooth field with no signs of azimuthal asymmetry or magnetic anomalies. The nearzero tilt of Saturn's dipole axis poses a challenge to dynamo theory, contradicting Cowling's Theorem. Additionally, the no detection of non-symmetric components in Saturn's magnetic field is puzzling, despite hints of potential longitudinal asymmetries near the planet. Cassini's arrival in 2004 offered a comprehensive three-dimensional sampling of magnetic field measurements. Observations during Cassini’s Grand Finale in 2017 suggested that Saturn's surface magnetic field could be accurately represented by a predominantly axisymmetric field, up to spherical harmonic degree 14, with only a negligible non-axisymmetric field contribution of 0.1%. Moreover, the magnetic field has not varied over the past three decades. Current dynamo models have not comprehensively explained the field's generation process or its unique characteristics. Despite significant progress in understanding Saturn's magnetic field, numerous questions persist. A holistic understanding demands precise information on Saturn's deep rotation period, atmospheric helium mass fraction, flow-induced gravity signals, and the impact of other physical processes, such as a shallower dynamo above the stable layer, varying electrical conductivity, and double-diffusive convection in the helium 'rain-out' layer, on magneto-hydrodynamic processes.