Cosmic streams bring random atoms and occasional nuclei in from the edges. Atoms collide and bind into planets. A dense world can naturally collapse into a core particle, then feed on matter drifting through the field. When extended planets touch, surface friction becomes grinding: heat and tangential motion tear loose hot dust instead of letting the worlds weld into one blob. When cores touch, friction transfers motion into spin and spin back into orbital motion. Place a strong gravity well nearby: inside its Roche limit, tidal forces can pull atoms from a body or tear a core back into a cloud.