Closed and open magnetic field lines (red and blue, respectively) near the OCFB of Ganymede’s magnetosphere. The feet of these lines are at the longitude of the auroral patches shown in Fig. 1 (one for each spin); the red lines start 1° equatorward of the OCFB, while the blue lines start 1° poleward. Juno-UVS observations performed during PJ 34 are projected onto Ganymede’s surface. The dashed white line is Juno’s trajectory, while the green cross is the projection of the spacecraft position during the closest approach. Panel a: 3D geometry of the magnetic field lines. Panels b and c: Projections as seen from above Ganymede and from Jupiter, respectively.