Why is Saturn's magnetic field almost perfectly symmetric about its spin axis?
In plain words
A theorem says a dynamo (the flowing-metal field generator inside a planet) cannot keep up a field that is perfectly symmetric around the rotation axis, yet Saturn's field is tilted by less than a hundredth of a degree. Something must hide the asymmetric part.
Precise statement
Cassini Grand Finale data bound Saturn's dipole tilt below about 0.01 degree, while Cowling's theorem forbids a dynamo-maintained axisymmetric field. Test whether a stably stratified, electrically conducting layer (for example from helium rain) with differential rotation filters non-axisymmetric harmonics strongly enough, consistently with gravity and ring-seismology constraints on interior structure. An answer is a self-consistent dynamo with such a layer reproducing the observed Gauss coefficients.
What would settle it
Dynamo simulations with interior structure from gravity and ring seismology reproducing Saturn's measured field spectrum.