Spin-period effects in magnetospheres with no axial tilt

A magnetic axis that is tilted with respect to the spin axis causes waves that generate spin-periodic effects in a planet's outer magnetosphere. Saturn's magnetic axis is aligned with its spin axis, and yet its outer magnetosphere exhibits spin-periodicities in all species of charged particles, just as expected from a wavy magnetodisk. In a spin-aligned geometry, however, a rotating anomaly (or cam'') in the inner magnetosphere can also generate spin-periodic waves by shaking the plasma sheet of the outer magnetosphere. Like a wobbling magnetodisk, this model predicts oscillations of the plasma sheet at distances beyond similar to 20 R(S) (1 R(S) = 60268 km). When viewed from a moving spacecraft, these oscillations cause charged particle periodicities near the spin period of the planet. The phase and polarity of these periodicities should change systematically with local time, and spin-periodic effects should appear along the magnetopause.