Energetic Neutral Atoms In Space: A Diagnostic Tool For Space Plasmas

This is a compendium on the remote sensing of space plasmas via energetic neutral atoms (ENAs). Covered are plasmas just above Earth's upper atmosphere, around other planets, at the heliospheric boundary, and in the local interstellar medium. ENAs stem from energetic singly-charged ions through charge exchange with ambient neutral atoms (ANAs), i.e. the constituents of the gas that coexists with the space plasma of interest. Being neutral, ENAs travel on ballistic trajectories - unfettered by magnetic fields that confine the plasmas - to well-placed ENA sensors where they provide remote information on composition, spatial, temporal, and energy distributions of space plasmas beyond the reach of the spacecraft, thus complementary to or in-lieu of in-situ ion measurements.This monograph presents the basic concepts and tools to appreciate the challenges in ENA-instrument design, data analysis, and model simulation, with examples from our first encounters with ENAs in space to ambitious upcoming missions. It is designed to provide a solid foundation, with an extensive list of references, for graduate students and researchers interested to engage in developing ENA instruments, analyzing ENA observations and/or proposing new missions to study remote space plasmas using novel ENA instruments.