Reconnection Preferentially Accelerates Light Ions at Ganymede's Magnetopause

Juno's flyby of Ganymede revealed ion composition in its vicinity with the Jovian Auroral Distributions Experiment–Ion (JADE-I) instrument. Throughout this flyby, we derive species-resolved ion density and velocity moments by decomposing the time-of-flight data into contributions from individual ion species using species-dependent fits. At the sub-Jovian flank magnetopause—a region previously linked to reconnection by previous studies—Juno encountered a strong field-aligned ion jet. Its direction and magnitude are consistent with Hall-mediated flank magnetopause reconnection at Ganymede. As reconnection-accelerated electrons have been associated with Ganymede's polar aurora, the persistence of auroral emission suggests reconnection, and associated ion acceleration may occur along an extended X-line. These results imply reconnection at Ganymede can act not only as a localized driver of ion jets, but also as a distributed pathway for ion and neutral loss. Given the appropriate reconnection geometry, such a mechanism is likely operating at a broad range of magnetized astrophysical bodies immersed within plasma.