Energetic Neutral Atom Fluxes from the Heliosheath: Constraints from in situ Measurements and Models

Fuselier, S. A.; Galli, André; Richardson, J. D.; Reisenfeld, D. B.; Zirnstein, E. J.; Heerikhuisen, J.; Dayeh, M. A.; Schwadron, N. A.; McComas, D. J.; Elliott, H. A.; Gomez, R. G.; Starkey, Michael; Kornbleuth, Marc; Opher, M.; Dialynas, K.

doi:10.3847/2041-8213/ac0d5c

Cited by 13 publications

(26 citation statements)

References 36 publications

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“…Furthermore, interplanetary shocks transmitted through the TS have been shown to result in further heating of the PUIs in the HS (Mostafavi et al 2019). Nonetheless, it should be noted that for ENAs of energies <1 keV, an alternative possible reason for the data-model discrepancy could be the source of these ENAs not being the HS but the VLISM, as discussed in Fuselier et al (2021).…”

Section: Discussionmentioning

confidence: 99%

On the Energization of Pickup Ions Downstream of the Heliospheric Termination Shock by Comparing 0.52–55 keV Observed Energetic Neutral Atom Spectra to Ones Inferred from Proton Hybrid Simulations

Gkioulidou

Opher

Kornbleuth

et al. 2022

ApJL

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We present an unprecedented comparison of ∼0.52–55 keV energetic neutral atom (ENA) heliosheath measurements, remotely sensed by the Interstellar Boundary Explorer (IBEX) mission and the Ion and Neutral Camera (INCA) on the Cassini mission, with modeled ENAs inferred from interstellar pickup protons that have been accelerated at the termination shock, using hybrid simulations, to assess the pickup ion energetics within the heliosheath. This is the first study to use hybrid simulations that are able to accurately model the acceleration of ions to tens of keV energies, which is essential in order to model ENA fluxes in the heliosheath, covering the full energy range observed by IBEX and CASSINI/INCA. The observed ENA intensities are an average value over the time period from 2009 to the end of 2012, along the Voyager 2 (V2) trajectory. The hybrid simulations upstream of the termination shock, where V2 crossed, are constrained by observations. We report an energy-dependent discrepancy between observed and simulated ENA fluxes, with the observed ENA fluxes being persistently higher than the simulated ones. Our analysis reveals that the termination shock may not accelerate pickup ions to sufficient energies to account for the observed ENA fluxes. We, thus, suggest that the further acceleration of these pickup ions is most likely occurring within the heliosheath, via additional physical processes like turbulence or magnetic reconnection. However, the redistribution of energy inside the heliosheath remains an open question.

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Section: Discussionmentioning

confidence: 99%

On the Energization of Pickup Ions Downstream of the Heliospheric Termination Shock by Comparing 0.52–55 keV Observed Energetic Neutral Atom Spectra to Ones Inferred from Proton Hybrid Simulations

Gkioulidou

Opher

Kornbleuth

et al. 2022

ApJL

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“… 2014 but also see Fuselier et al. 2021 ). The latitudinal ordering of ENA energy spectra around solar wind energy probably reflects the different solar wind speed for equatorial and polar heliodirections (Desai et al.…”

Section: Observations Of Energetic Neutral Atoms and Interstellar Neu...mentioning

confidence: 92%

“…Any feasible mechanism must account for the observational fact that the GDF is also observed from the downwind heliosphere direction. For the GDF spectrum around solar wind energy (above 0.5 keV), PUIs in the heliosheath may suffice (Galli et al 2014;Zirnstein et al 2014 but also see Fuselier et al 2021). The latitudinal ordering of ENA energy spectra around solar wind energy probably reflects the different solar wind speed for equatorial and polar heliodirections (Desai et al 2015).…”

Section: The Globally Distributed Signal Of Energetic Neutral Atoms F...mentioning

confidence: 99%

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The Heliosphere and Local Interstellar Medium from Neutral Atom Observations at Energies Below 10 keV

et al. 2022

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As the heliosphere moves through the surrounding interstellar medium, a fraction of the interstellar neutral helium, hydrogen, and heavier species crossing the heliopause make it to the inner heliosphere as neutral atoms with energies ranging from few eV to several hundred eV. In addition, energetic neutral hydrogen atoms originating from solar wind protons and from pick-up ions are created through charge-exchange with interstellar atoms.This review summarizes all observations of heliospheric energetic neutral atoms and interstellar neutrals at energies below 10 keV. Most of these data were acquired with the Interstellar Boundary Explorer launched in 2008. Among many other IBEX breakthroughs, it provided the first ever all-sky maps of energetic neutral atoms from the heliosphere and enabled the science community to measure in-situ interstellar neutral hydrogen, oxygen, and neon for the first time.These observations have revolutionized and keep challenging our understanding of the heliosphere shaped by the combined forces of the local interstellar flow, the local interstellar magnetic field, and the time-dependent solar wind.

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“…This discrepancy between the PLS and CG speeds is key to understanding the HSH; we need to determine whether the PLS or CG (CRS and LECP) V R values are correct. These values are used to verify global MHD models and to calculate ENA fluxes for comparison with data (Fuselier et al 2021). One way to distinguish between these two data sets is to compare the magnetic flux measured at 1 au to that obtained using the different Voyager velocity profiles.…”

Section: Introduction To the Heliosheathmentioning

confidence: 99%

Using Magnetic Flux Conservation to Determine Heliosheath Speeds

Richardson

Cummings

Burlaga

et al. 2021

ApJL

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The heliosheath (HSH) radial speeds at Voyager 2 (V2) derived from the plasma instrument (PLS) and from particle instruments using the Compton-Getting (CG) effect are different. At V2 the CG speeds are more variable than the plasma speeds and decrease about 2 yr before the heliopause. We use magnetic flux conservation to differentiate between these two speed profiles at V2, comparing the magnetic flux observed at 1 au and in the HSH. For V2 the PLS speed profile is significantly more consistent with magnetic flux conservation than the CG speeds. For Voyager 1 (V1), we present new V R derivations from the Cosmic Ray Subsystem (CRS) using the CG method that agree reasonably well with those previously obtained from the low energy charged particle (LECP) instrument. If we use the V2 PLS speed profile to calculate the magnetic flux at V1, we again find much better agreement than if we use the V1 CG speeds. These results suggest that the radial speeds derived from particle anisotropy observations in the HSH are not reliable.

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Energetic Neutral Atom Fluxes from the Heliosheath: Constraints from in situ Measurements and Models

Cited by 13 publications

References 36 publications

On the Energization of Pickup Ions Downstream of the Heliospheric Termination Shock by Comparing 0.52–55 keV Observed Energetic Neutral Atom Spectra to Ones Inferred from Proton Hybrid Simulations

On the Energization of Pickup Ions Downstream of the Heliospheric Termination Shock by Comparing 0.52–55 keV Observed Energetic Neutral Atom Spectra to Ones Inferred from Proton Hybrid Simulations

The Heliosphere and Local Interstellar Medium from Neutral Atom Observations at Energies Below 10 keV

Using Magnetic Flux Conservation to Determine Heliosheath Speeds

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