The Local Interstellar Magnetic Field Observed by Voyager 1 and IBEX

Abstract

Observations by the Interstellar Boundary Explorer (IBEX) have revealed the presence of the IBEX Ribbon, an almost circular band of increased ENA emissions that is believed to be centered on the direction of the interstellar magnetic field. IBEX measures a range of interstellar species including H, He, and O. IBEX has been able to distinguish primary He coming directly from the interstellar medium from secondary He that is created through neutralization of He+ atoms in the heliosheath. Together with the observations of Lyman-α radiation from SOHO/SWAN, which is resonantly absorbed and re-emitted from interstellar H atoms that move into the heliosphere, the directions of interstellar flow for each of the observed interstellar species (H, primary He, secondary He, and primary O) line-up along a symmetry plane — the interstellar B–V plane — that should contain the interstellar magnetic field direction (B) and the interstellar flow direction (V). The B–V plane also contains the center of the IBEX Ribbon, which supports the concept that the Ribbon center is close to the direction of the interstellar magnetic field. Further, the deflection of the various interstellar species along the B–V plane are consistent with the compression of the heliosheath by the interstellar magnetic field pressure. Lastly, the interstellar magnetic field in the outer heliosheath is directly observed by Voyager 1 (V1). The direction of the interstellar magnetic field observed by V1 is offset from the Ribbon center, consistent with draping around the heliopause, and time variations in the interstellar magnetic field are consistent with the effects of large-scale compression and rarefaction in the outer heliosheath. Thus, we summarize the array of observations that suggest a consistent direction of the interstellar magnetic field, and the effects of the interstellar magnetic field on the structure and time variations in the heliosheath.