Toward a Model of Planetary Rotation

A simple computer simulation of protoplanet growth was written with a view to explaining planetary rotation, using simplified overall planet models with iron cores and less dense mantles–silicate for terrestrial planets and solid hydrogen for giant planets. The general trend of increasing rotational kinetic energy with increasing mass was maintained (r 2 0.78 versus the actual r 2 0.99). Deviations from the expected results seem to correlate with relative density effects, in that gas giants (Jupiter, Saturn, β Pictoris b) fell below the expected line while ice giants (Uranus, Neptune) fell above it. This implies that improvements in the model could eventually help better understand the origin of planetary rotation periods.