The Role of Planetary Rotation in Polar Cusp Localization

Abstract Juno observations have revealed that Jupiter's polar cusps are displaced toward dusk and even the nightside, contradicting the Earth‐derived paradigm that is confined to narrower ranges near noon. These findings underscore the overlooked influence of planetary rotation on magnetospheric dynamics, exposing a critical gap in current theoretical frameworks. Using global magnetohydrodynamic (MHD) simulations, we show that high‐altitude cusps reside on the dusk hemisphere at both Saturn and Jupiter, consistent with Juno data at Jupiter and distinct from Earth's near‐noon‐centered cusps. Controlled experiments with artificially increased Earth rotation rates demonstrate a systematic duskward shift of cusp local time, transitioning from noon to afternoon (Saturn‐like) and dusk (Jupiter‐like) sectors. We propose the corotation‐to‐convection speed ratio as a unifying parameter that captures this duskward displacement across different planets. This unified framework explains gas‐giant magnetospheres, offering potential applications to other rapidly rotating systems, such as ice giants, early Earth, and exoplanets.