Evidence of a Thick Heliopause Boundary Layer Resulting from Active Magnetic Reconnection with the Interstellar Medium

Drew L. Turner, Adam Michael, Elena Provornikova, Marc Kornbleuth, Merav Opher, Stefan Eriksson, Benoit Lavraud, Parisa Mostafavi, Matthew E. Hill, Pontus Brandt, Ian J. Cohen, Joseph Westlake, John D. Richardson, Nathan A. Schwadron, David J. McComas

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Voyager 1 and 2 data from the vicinity of the heliopause and very local interstellar medium are reexamined to better understand the confounding lack of rotation in the magnetic field (B-field) across the heliopause observed by both Voyagers, despite their very large spatial separations (>100 au). Using three estimates for the orientation of the B-field in the pristine interstellar medium and four models of the heliosphere, we calculate draped interstellar B-field orientations along the model heliopauses and compare those estimates to the Voyager observations. At both Voyagers, expected draped B-fields are inconsistent with the observed B-field orientations after the boundary crossings. Furthermore, we show how the longer-term trends of the observed B-fields at both Voyagers after the crossings actually rotated away from both the expected draped B-field and the pristine interstellar B-field directions. We develop evidence, including an illustrative and analogous set of observations from Magnetospheric Multiscale spacecraft along Earth’s magnetopause, in support of a hypothesis that both Voyagers transited a thick boundary layer of reconnected magnetic flux along the heliopause surface. We estimate that Voyager 1 has not yet fully transited this boundary layer, the radial thickness of which at the Voyager 1 crossing location may be >18 au and likely much thicker. Meanwhile, at Voyager 2's crossing location, the boundary layer is likely much thinner, and for Voyager 2, we present evidence that Voyager 2 might already have transited the boundary layer and entered a region of fields and plasma that were never connected to the Sun—the very local interstellar medium.

Original languageEnglish (US)
Article number130
JournalAstrophysical Journal
Issue number2
StatePublished - Jan 1 2024

All Science Journal Classification (ASJC) codes

  • Astronomy and Astrophysics
  • Space and Planetary Science


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