Global perspective of the Local Interstellar Magnetic Field (LISMF) as it drapes around the heliopause. Results are derived from a model fit to the IBEX Ribbon ENA data (Zirnstein et al. 2016). LEFT: LISMF lines (black curves) and magnetic field magnitude (colored background) inferred from the configuration of the Ribbon. The black arrows roughly indicate vectors in Voyager 1’s direction (V1), the interstellar inflow direction (ULISM), and the Voyager 2 direction (V2) projected into the meridional plane. RIGHT: Unfolding of the simulated LISMF components along the Voyager 1 (top), Upstream (middle; opposite to the interstellar inflow), and Voyager 2 (bottom) directions from the heliopause out to 1,000 au, including how the angle of the magnetic field changes over radial distance (black lines) and how the magnitude of the magnetic field changes with respect to the unfolded direction at 1,000 au |BLISM| (red). The vertical yellow lines highlight each spacecraft’s location during the year of 2022.
Prior to the Voyagers’ heliopause crossings, models and the community expected the magnetic field to show major rotations across the boundary. Surprisingly, the field showed no significant change in direction from the heliospheric Parker Spiral at either Voyager location. Meanwhile, a major result from the IBEX mission is the derived magnitude and direction of the interstellar field far from the Sun (∼1000 au) beyond the influence of the heliosphere. Using a self-consistent model fit to IBEX ribbon data, Zirnstein et al. reported that this “pristine” local interstellar magnetic field has a magnitude of 0.293 nT and direction of 227° in ecliptic longitude and 34°.6 in ecliptic latitude. These values differ by 27% (51%) and 44° (12°) from what Voyager 1 (2) currently observes (as of ∼2022.75). While differences are to be expected as the field undrapes away from the heliosphere, the global structure of the draping across hundreds of astronomical units has not been reconciled. This leads to several questions: How are these distinct sets of observations reconcilable? What is the interstellar magnetic field’s large-scale structure? How far out would a future mission need to go to sample the unperturbed field? Here, we show that if realistic errors are included for the difficult-to-calibrate radial field component, the measured transverse field is consistent with that predicted by IBEX, allowing us to answer these questions through a unified picture of the behavior of the local interstellar magnetic field from its draping around the heliopause to its unfolding into the pristine interstellar medium.