Kelvin–Helmholtz Instability and Energetic Neutral Atoms in the Heliosphere

Abstract The Interstellar Mapping and Acceleration Probe (IMAP) mission launched from Earth on 2025 September 24, beginning its commissioning phase as the spacecraft makes its way to Lagrange Point 1. IMAP-Hi, one of three energetic neutral atom (ENA) imagers, has improved capabilities compared to its predecessor, the Interstellar Boundary Explorer-Hi instrument, such as a wider energy coverage (∼0.4–15.6 keV compared to ∼0.5–6 keV). In this study, we aim to simulate ENA emissions from the heliosphere, at IMAP-Hi energies, with the goal of showing what ENA maps may look like when their source is affected by the presence of the Kelvin–Helmholtz instability (KHI). The KHI arises when the fast and slow solar wind meet in the heliosheath near the heliopause and create a shear flow, usually strongest at high latitudes. According to our simulation, if the KHIs are present in the heliosphere, then IMAP-Hi should be able to observe their effects on ENA emissions via long bands of enhanced ENA fluxes at high northern and southern latitudes, reaching all the way back to the tail. These bands are separated on the order of ∼15° in latitude, depending on the direction in the sky. The ENA bands are most visible at ∼2–6 keV. The presence or absence of ENA bands in IMAP-Hi observations and their orientation may not only provide important information about the structure of the heliosphere, but also guide improvements to our models, since these features differ or are not present among various simulations.