The Astrophysical Journal | VOL. 870

Energetic Neutral Atoms from the Heliosheath as an Additional Population of Neutral Hydrogen in the Inner Heliosphere

Publication Date Jan 8, 2019


Interstellar neutral hydrogen (ISN H) gas penetrates freely the heliopause. Inside the inner heliosheath, the chargeexchange interaction of this gas with the shocked solar wind and pickup ions creates energetic neutral atoms (ENAs). ISN H is strongly depleted inside the termination shock but a fraction reaches the Earth’s orbit. In these regions of the heliosphere, ISN H is the source population for interstellar pickup ions and for the heliospheric backscatter glow. The globally distributed flux (GDF) of ENAs created in the inner heliosheath has been sampled directly by the Interstellar Boundary Explorer. Based on these measurements, we calculate the density of the GDF ENA population at the Earth’s orbit. We find that this number density is between 10⁻⁴ and 10⁻³ cm⁻³, i.e., comparable in magnitude to the number density of ISN H in the downwind portion of the Earth’s orbit. Half of this atom population has energies less than ~80 eV. This GDF population of neutral hydrogen is likely to provide a significant contribution to the intensity of heliospheric glow in the downwind hemisphere, may be the source of the inner source of hydrogen pickup ions, and may be responsible for the excess of production of pickup ions found in the analysis of magnetic wave events induced by the proton pickup process in the downwind region at 1 au from the Sun.


Energetic Neutral Atoms Pickup Ions Interstellar Boundary Explorer Interstellar Neutral Hydrogen Shocked Solar Wind Flux Of Energetic Neutral Atoms Downwind Region Neutral Hydrogen Neutral Hydrogen Gas Intensity Of Glow

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No potential conflict of interest was reported by the authors. The conception and design of the study, acquisition of data, analysis and interpretatio...

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