Modeling Emission of Heavy Energetic Neutral Atoms from the Heliosphere

TL;DR

This paper models the emission of heavy energetic neutral atoms from the heliosphere, predicting their intensities and discussing the potential for future detection to improve understanding of heliospheric processes.

Contribution

It provides the first estimates of heavy ENA emissions from the heliosphere and discusses their potential for future observational studies.

Findings

Helium ENA fluxes are the largest among heavy species.

Heavy ENA intensities are 50-10^6 times smaller than hydrogen ENAs.

Detection requires future instruments capable of mass measurement.

Abstract

Observations of energetic neutral atoms (ENAs) are a fruitful tool for remote diagnosis of the plasma in the heliosphere and its vicinity. So far, instruments detecting ENAs from the heliosphere were configured for observations of hydrogen atoms. Here, we estimate emissions of ENAs of the heavy chemical elements helium, oxygen, nitrogen, and neon. A large portion of the heliospheric ENAs is created in the inner heliosheath from neutralized interstellar pick-up ions (PUIs). We modeled this process and calculated full-sky intensities of ENAs for energies 0.2-130 keV/nuc. We found that the largest fluxes among considered species are expected for helium, smaller for oxygen and nitrogen, and smallest for neon. The obtained intensities are 50-10^6 times smaller than the hydrogen ENA intensities observed by IBEX. The detection of heavy ENAs will be possible if a future ENA detector is equipped with the capability to measure the masses of observed atoms. Because of different reaction cross-sections among the different species, observations of heavy ENAs can allow for a better understanding of global structure of the heliosphere as well as the transport and energization of PUIs in the heliosphere.