Can IBEX Identify Variations in the Galactic Environment of the Sun using Energetic Neutral Atom (ENAs)?

TL;DR

This paper demonstrates that IBEX ENA observations can detect variations in the galactic environment around the Sun, revealing how interstellar conditions influence the heliosphere boundary through modeling and analysis of ENA fluxes.

Contribution

The study introduces a model-based approach to predict ENA flux variations due to changes in the interstellar environment, showing IBEX's capability to detect these variations.

Findings

Approximately 20% of IBEX pixels can detect model differences at 3 sigma.

ENA fluxes vary with the solar transition into different interstellar clouds.

The Ribbon phenomenon traces heliosphere distortions caused by interstellar pressures.

Abstract

The Interstellar Boundary Explorer (IBEX) spacecraft is providing the first all-sky maps of the energetic neutral atoms (ENAs) produced by charge-exchange between interstellar neutral \HI\ atoms and heliospheric solar wind and pickup ions in the heliosphere boundary regions. The 'edge' of the interstellar cloud presently surrounding the heliosphere extends less than 0.1 pc in the upwind direction, terminating at an unknown distance, indicating that the outer boundary conditions of the heliosphere could change during the lifetime of the IBEX satellite. Using reasonable values for future outer heliosphere boundary conditions, ENA fluxes are predicted for one possible source of ENAs coming from outside of the heliopause. The ENA production simulations use three-dimensional MHD plasma models of the heliosphere that include a kinetic description of neutrals and a Lorentzian distribution for ions. Based on this ENA production model, it is then shown that the sensitivities of the IBEX 1.1 keV skymaps are sufficient to detect the variations in ENA fluxes that are expected to accompany the solar transition into the next upwind cloud. Approximately 20% of the IBEX 1.1 keV pixels appear capable of detecting the predicted model differences at the $ 3 \sigma$ level, with these pixels concentrated in the Ribbon region. Regardless of the detailed ENA production model, the success of the modeled \BdotR\ directions in reproducing the Ribbon locus, together with our results, indicate that the Ribbon phenomenon traces the variations in the heliosphere distortion caused by the relative pressures of the interstellar magnetic and gaseous components.