Energetic neutral atoms from the heliosheath as an additional population of neutral hydrogen in the inner heliosphere

Abstract

Interstellar neutral hydrogen (ISN H) gas penetrates freely the heliopause. Inside the inner heliosheath, the charge-exchange 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 Interstellar Boundary Explorer (IBEX). 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 have energies less than $\sim 80$ 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.

arXiv commentAccepted for publication in Ap.J

References in corpus (9)

• Local Interstellar Neutral Hydrogen sampled in-situ by IBEX
• Neutral H density at the termination shock: a consolidation of recent results
• Interstellar Neutral Gas Species And Their Pickup Ions Inside The Heliospheric Termination Shock. Ionization Rates For H, O, Ne, And He
• Evolution of the Solar Lyman-Alpha line profile during the solar cycle
• Distance to the IBEX Ribbon Source Inferred from Parallax
• Local Interstellar Hydrogen's Disappearance at 1 Au: Four Years of IBEX in the Rising Solar Cycle
• The downwind hemisphere of the heliosphere: Eight years of IBEX-Lo observations
• Evolution of the solar Ly-$\alpha$ line profile during the solar cycle. II. How accurate is the present radiation pressure paradigm for interstellar neutral H in the heliosphere?
• The energy-dependent position of the IBEX ribbon due to the solar wind structure

Cited by in corpus (1)

• Interstellar Neutral Hydrogen in the Heliosphere: New Horizons Observations in the Context of Models