Viewing Global Changes in the Heliosheath with IMAP’s Energetic Neutral Atom Imagers

We present a simulation analysis of NASA’s upcoming Interstellar Mapping and Acceleration Probe (IMAP) energetic neutral atom (ENA) instrument capabilities in viewing “global” changes in the heliosheath (HS) plasma, and the resulting ENA flux changes detected near Earth. This is done by simulating ENA emissions produced by charge exchange in a simulated heliosphere, utilizing the instruments’ energy coverage, and calculating the time it takes for the SW to travel from 1 au to the HS and for ENAs to travel back. We aim to answer the following: (i) What are the time delays as a function of energy and direction; (ii) at what energies can we observe changes the soonest; and (iii) what might the ENA source distributions affecting the time delays look like? We find the following: (i) The time delay depends on energy and direction in the sky, taking from >20 yr to <2 yr to see a response. The time delay does not decrease monotonically with increasing ENA energy, because of the energy-dependent, H+p charge exchange cross section. (ii) The quickest changes can be observed at ∼15 keV (without HS energy diffusion), intersecting IMAP-Hi and IMAP-Ultra energies. (iii) The ENA source distributions, and how far out IMAP can “see” the heliosphere, strongly depend on energy: IMAP-Lo and IMAP-Ultra should be able to view the farthest back in the heliotail but with long delay times. Finally, we show how energy diffusion in the HS affects the time delays and ENA source distributions, increasing ENA fluxes and prolonging time delays.