The dipole component of the magnetic field at the magnetic equator of Neptune is about 14 microteslas (0.14 G). The dipole magnetic moment of Neptune is about 2.2 1017 Tm3 (14 TRN3, where RN is the radius of Neptune). Neptune's magnetic field has a complex geometry that includes relatively large contributions from non-dipolar components, including a strong quadrupole moment that may exceed the dipole moment in strength. By contrast, Earth, Jupiter and Saturn have only relatively small quadrupole moments, and their fields are less tilted from the polar axis. The large quadrupole moment of Neptune may be the result of offset from the planet's centre and geometrical constraints of the field's dynamo generator.
Is there an answer to this question (If it cannot be answered, say "unanswerable"): Besides the geometrical constraints of Neptune's dynamo generator, what is another reason of the quadrupole moment?
unanswerable