Implications of the Voyager 1 and 2 Magnetic Field Directions on the Energetic Neutral Atom Ribbon

The interstellar magnetic field direction can be inferred from the position of the energetic neutral atom (ENA) Ribbon observed by Interstellar Boundary EXplorer (IBEX) and Voyager 1 and 2 in situ measurements. Since their heliopause crossing, the Voyager field directions have been substantially different from those indicated by the ENA Ribbon. Furthermore, the field directions and magnitudes differ between the two Voyagers, which may be attributable to draping. However, no substantial undraping toward the Ribbon direction is seen thus far in the Voyager data. Recently, J. S. Rankin et al. suggested that this discrepancy may arise from the absence of a direct calibration of the radial magnetic field component on the Voyager spacecraft. In this study, we employ a complementary method to test the Voyager magnetic field directions. We use the reported Voyager magnetic field directions and the electron density from the Voyager 1 plasma wave instrument to model expected ENA Ribbon features, based on a simplified analytic secondary ENA model, arriving from between the heliopause and the Voyager 1 and 2 locations (169 and 141 au, respectively, at the end of 2025). The observed IBEX Ribbon represents the fluxes beyond their current distances, which we use to normalize the model. The resulting Ribbon feature fluxes with the Voyager magnetic fields, which, at this time, represent ≈50% of the total for Voyager 1, are inconsistent with the IBEX observations. However, when solely modifying the radial component of the Voyager 2 magnetic field according to a global heliospheric model, the resulting Ribbon feature is reconcilable with structures observed by IBEX.