On the role of near-planetary particle swarms in the origin of spin.

The process by which a planet acquired angular momentum during its growth from small particles moving about the sun in the same direction as the planet's orbital motion is analyzed by reducing the problem to two two-body problems involving particle motion in the sun's gravitational field and in the planet's sphere of influence. The special cases of 'symmetric' particle orbits and 'asymmetric' particle swarms are considered, and analytical expressions are obtained for the total angular momentum and the total mass added to a planet in each case. The effect of the thickness of the layer in which the particles move is also taken into account. Numerical results computed for the nine planets as a function of eccentricity are presented which indicate that during the epoch of planet formation all the planets except Mercury and Venus were encircled by small-particle swarms with radii at least ten times larger than those of the planets themselves, that the unaccreted remnants of swarms became planetary satellites, and that Pluto should possess a satellite.