Probing the Earth's Magnetosheath Boundaries Using the Interstellar Boundary Explorer Encounters

Abstract:

The primary objective of the Interstellar Boundary Explorer (IBEX) mission is to detect energetic neutral atoms (ENAs) created at the boundaries of our heliosphere. However, IBEX’s highly eccentric orbital configuration enables it to spend ~15% of its time inside the Earth’s magnetosheath. When IBEX is in the magnetosheath, its sensors detect a clear in situ background signal that can be over 10 times the typical count rate of remotely measured ENAs, the source of this background signal being deflected magnetosheath ions colliding with the sensor, charge exchanging into neutrals within the sensor, and continuing through the remaining subsystems. We investigate IBEX encounters with the magnetosheath boundaries using ~10 years of orbital data, and we determine the magnetopause and bow shock locations inferred from this background signal. We find 300 bow shock crossings from ~11 R_e upstream to ~36 R_e downstream and 271 magnetopause crossings from ~6 R_e upstream to ~48 R_e downstream. In this paper, we demonstrate how IBEX can be used to identify magnetosheath crossings, and extend boundary observations well past the terminator into previously unexplored regions of the magnetosheath, thus further constraining future models of magnetosheath boundaries. Additionally, we show that our method of determining magnetosheath boundary crossings is also capable of identifying passing interplanetary coronal mass ejections.