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Peer-reviewedCC BY 4.0The Astrophysical Journal Supplement Series

The Velocity Distribution of Heliosheath-created Pickup Ions along Voyager 2’s Trajectory and Energetic Neutral Atom Fluxes

  • Senbei Du1
  • Merav Opher1
  • Marc Kornbleuth1
  • Ethan Schuyler Bair1
  • Joe Giacalone2
  • Jeewoo Park3
  1. 1Boston University
  2. 2University of Arizona
  3. 3University of Maryland
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Abstract

We use Voyager 2 measurements of plasma parameters and magnetic field to constrain energetic neutral atom (ENA) fluxes observed by Interstellar Boundary Explorer (IBEX). Unlike previous ENA models, our calculation does not directly use the ion distributions from global heliosphere simulations. Instead, we model the pickup ion velocity distributions based on previous kinetic simulations of the termination shock and the expected energy-dependent charge-exchange rate in the heliosheath based on Voyager 2 observations. The effects of flow compression on the ion distributions are quantified. Motivated by the recent finding that the newborn pickup ions in the heliosheath may maintain anisotropy, we consider both the isotropic limit and the anisotropic limit with no pitch-angle scattering. We also use hybrid kinetic simulations with continued pickup ion injection to investigate the evolution of the anisotropy due to self-generated kinetic instabilities. In all cases, the modeled ENA fluxes significantly underpredict the IBEX observations, especially in low energies (between about 0.05 and 1 keV), confirming previous global-simulation-based studies. We explore several possible explanations for this discrepancy, such as magnetic reconnection, uncertainties in the heliosheath flow speed, and additional ENA sources in the interstellar medium.

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Cite

BibTeXRIS
BibTeX
@article{du2026velocity,
  title = {{The Velocity Distribution of Heliosheath-created Pickup Ions along Voyager 2’s Trajectory and Energetic Neutral Atom Fluxes}},
  author = {Senbei Du and Merav Opher and Marc Kornbleuth and Ethan Schuyler Bair and Joe Giacalone and Jeewoo Park},
  journal = {The Astrophysical Journal Supplement Series},
  year = {2026},
  month = oct,
  doi = {10.3847/1538-4365/aea206},
  url = {https://iopscience.iop.org/article/10.3847/1538-4365/aea206},
  note = {CC BY 4.0},
}
RIS
TY  - JOUR
TI  - The Velocity Distribution of Heliosheath-created Pickup Ions along Voyager 2’s Trajectory and Energetic Neutral Atom Fluxes
AU  - Senbei Du
AU  - Merav Opher
AU  - Marc Kornbleuth
AU  - Ethan Schuyler Bair
AU  - Joe Giacalone
AU  - Jeewoo Park
PY  - 2026
DA  - 2026/10/07
JO  - The Astrophysical Journal Supplement Series
DO  - 10.3847/1538-4365/aea206
UR  - https://iopscience.iop.org/article/10.3847/1538-4365/aea206
AB  - We use Voyager 2 measurements of plasma parameters and magnetic field to constrain energetic neutral atom (ENA) fluxes observed by Interstellar Boundary Explorer (IBEX). Unlike previous ENA models, our calculation does not directly use the ion distributions from global heliosphere simulations. Instead, we model the pickup ion velocity distributions based on previous kinetic simulations of the termination shock and the expected energy-dependent charge-exchange rate in the heliosheath based on Voyager 2 observations. The effects of flow compression on the ion distributions are quantified. Motivated by the recent finding that the newborn pickup ions in the heliosheath may maintain anisotropy, we consider both the isotropic limit and the anisotropic limit with no pitch-angle scattering. We also use hybrid kinetic simulations with continued pickup ion injection to investigate the evolution of the anisotropy due to self-generated kinetic instabilities. In all cases, the modeled ENA fluxes significantly underpredict the IBEX observations, especially in low energies (between about 0.05 and 1 keV), confirming previous global-simulation-based studies. We explore several possible explanations for this discrepancy, such as magnetic reconnection, uncertainties in the heliosheath flow speed, and additional ENA sources in the interstellar medium.
SN  - 0067-0049
SN  - 1538-4365
ER  -