Enhanced Ion Escape Rate During IMF Rotation Under Weak Intrinsic Magnetic Field Conditions on a Mars‐Like Planet

Abstract

AbstractThe rotation of the interplanetary magnetic field (IMF) provides details of the escape mechanism that varies with the interaction between the intrinsic magnetic field and the IMF. A multispecies magnetohydrodynamic simulation is conducted on a Mars‐like planet under the conditions of a weak intrinsic magnetic field and the IMF rotating by 180° over 12 hr, which is comparable to the coronal mass ejection (CME) time scale. The total ion escape rate increases from ∼5 × 1023 s−1 to ∼3 × 1025 s−1 during the IMF rotation from due north (parallel to the assumed intrinsic magnetic field) to due south (antiparallel to the assumed intrinsic magnetic field). The escape rate increases significantly with the IMF rotating from due north to clock angles of 45°–75°, followed by a gentle increase until the IMF rotates to due south. The trigger for the large increase is multiple reconnections in the magnetospheric flank region, and the subsequent increase is due to the expansion of the reconnection area into the equatorial region. The IMF mass loading in the ionosphere is also responsible for the gentle increase with IMF clock angles above 90° in addition to the flank reconnection. The IMF rotation is a general feature for a CME. Exoplanets orbiting in the vicinity of M‐dwarfs might be frequently affected by IMF rotation, as they could be exposed to severe stellar winds such as in CME environments, and the current study could be helpful for future planned observations of the exoplanetary environment.