Fig. 4: Magnetic topology analysis using suprathermal electron measurements and the shape parameter.

a, The pitch angle distribution from SWEA measurements (SWE PAD) of 111–140 eV electrons. b, The shape parameters for electrons moving towards (red) and away from (green) the planet. The vertical dashed lines are positioned as in Figs. 2 and 3, marking the exhaust boundaries. c–f, The electron energy spectra in parallel (0–30°) and antiparallel (150–180°) directions at times indicated by the thick vertical dashed lines labelled ‘c’ (c), ‘d’ (d), ‘e’ (e) and ‘f’ (f) in a and b. ALT, altitude; SCP, spacecraft potential estimated by SWEA. The one-sided loss cone outside the exhaust region in a (orange bars at top) suggests open magnetic field lines²⁹. A characteristic photoelectron peak⁴⁴ can be identified in the parallel spectrum at 20:50:23 ut in c and in the antiparallel spectrum at 20:52:59 ut in f, while the electron spectra in the opposite directions show no photoelectron signals. The 20:51:21 ut electron spectra in d and the 20:52:11 ut electron spectra in e, in both parallel and antiparallel directions, show typical features of solar wind electrons, suggesting that magnetic field lines in the exhaust connect to the solar wind at both ends.