The Sun has by far the lowest moment of inertia factor value among Solar System bodies; it has by far the highest central density (162 g/cm3,[3][note 3] compared to ~13 for Earth[4][5]) and a relatively low average density (1.41 g/cm3 versus 5.5 for Earth).
[6] Ganymede has the lowest moment of inertia factor among solid bodies in the Solar System because of its fully differentiated interior,[7][8] a result in part of tidal heating due to the Laplace resonance,[9] as well as its substantial component of low density water ice.
Callisto is similar in size and bulk composition to Ganymede, but is not part of the orbital resonance and is less differentiated.
[10][11] The polar moment of inertia is traditionally determined by combining measurements of spin quantities (spin precession rate and/or obliquity) with gravity quantities (coefficients of a spherical harmonic representation of the gravity field).
For bodies in hydrostatic equilibrium, the Darwin–Radau relation can provide estimates of the moment of inertia factor on the basis of shape, spin, and gravity quantities.
[26] The moment of inertia factor provides an important constraint for models representing the interior structure of a planet or satellite.