A striking correlation has been noted between planet's magnetic and inertial moments. One possible explanation for this relationship could be that dynamo action, responsible for creating the planet's magnetic field, is closely tied to its rotation. A dynamo is an energy-producing machine that generates magnetic energy by moving electrically conducting fluid such as molten iron in its core. As the planet rotates, so too does this fluid within its core which further amplifies its magnetism.
The magnetic field produced by a dynamo is determined by the planet's rate of fluid motion, which in turn depends on its moment of inertia. The larger this number is, the slower its rotation and weaker its core fluid motion - leading to weaker magnetic fields.
Conversely, the magnetic moment of a planet is determined by both its strength of magnetic field and size. A larger field results in larger magnetic moments; on the contrary, weaker magnets caused by increased inertia would result in smaller magnetisms.
Your data clearly illustrates the correlation between planet's magnetic and inertial moments, with some exceptions such as Venus' and Mars' retrograde rotation which may explain their anomalous magnetic fields.
In conclusion, the relationship between planet's magnetic and inertial moments can be explained by the connection between their rotation, fluid motion in their core, and the generated magnetic field.
