For some time, astronomers have theorized that there is a connection between planetary mass and rotation. In the solar system, Jupiter and Saturn both rotate rapidly, completing a rotation in roughly ten hours, while accounting for a significant fraction of the solar system's rotational energy. Using the W.M. Keck Observatory on Maunakea, Hawai'i, a team of astronomers tested this predicted relationship by studying 32 gas giants and brown dwarfs in distant star systems—6 giant planets larger than Jupiter and 25 brown dwarf companions.