Energy Dissipation Mechanisms at the Bow Shock of an Outer Planet – Jupiter

Recent observations of Jupiter's bow shock have provided new insights into the energy dissipation mechanisms associated with bow shocks of outer planets. The typical Alfvénic Mach number increases from ~8 to >20 as we move outward from the Sun, from Earth to Jupiter. Research on Earth’s bow shock suggests that plasma waves (e.g., ion-acoustic waves, waves driven by the electron cyclotron drift instability (ECDI), electrostatic solitary waves, and whistler mode waves) play a critical role in converting solar wind ram energy into thermal energy. However, the lack of high-resolution plasma wave data, which is essential for detecting these waves, has previously hindered their identification at the outer planets. In this article, based on two case studies, we demonstrate that similar waves also exist at the Jovian bow shock. However, unlike their terrestrial counterparts, Ion-acoustic waves at Jupiter may display harmonic structures, indicating possible particle trapping, and intense ECDI may occur to accommodate the shock's intensity. Magnetic field measurements reveal clear shock reformation, and particle observations indicate modulation of the reflected ion number density by ultra-low-frequency waves.