The solar system stores its mass and its spin in different places. The Sun holds almost all the mass, yet the planets carry over ninety-nine percent of the angular momentum in their orbits around it.
The explanation starts in the protoplanetary disk, the rotating cloud of gas and dust from which the system formed. Gravity pulled most of the material inward, building a dense central star. Conservation of angular momentum kept the disk rotating, so orbital motion in the outer regions retained a large share of the system’s total rotational budget even as mass streamed toward the center.
The young Sun then shed angular momentum through magnetic braking. Its magnetic field coupled the stellar wind to the star’s rotation, creating a torque that slowed the solar spin while carrying angular momentum away. Viscous transport and gravitational interactions in the disk moved additional angular momentum outward, where forming planets locked it into stable Keplerian orbits. The result is a compact, massive star with relatively low spin and a set of lighter planets that hold the dominant rotational inertia in their motion around it.
