Emission of hydrogen energetic neutral atoms from the Martian subsolar magnetosheath

Wang, X.‐D.; Alho, Markku; Järvinen, R.; Kallio, Esa; Barabash, S.; Futaana, Yoshifumi

doi:10.1002/2015ja021653

Cited by 12 publications

(19 citation statements)

References 60 publications

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“…As shown in Figure , the direction of the proton velocity from the hybrid run increasingly deviates from symmetric flow, dominantly flowing toward the − E c direction, as they approach the IMB, where the neutral density increases exponentially. Such a flow pattern is caused by the combination of the finite gyroradius effect of the solar wind protons and the addition of the locally born planetary ions to the flow (Wang et al, ). The produced H‐ENAs therefore have a higher − E c ‐directed velocity component at a lower altitude in the magnetosheath.…”

Section: Simulation Results: Solar Wind H‐enasmentioning

confidence: 99%

“…In this work, we use the same three‐dimensional global hybrid model for the Mars‐solar wind interaction and analyze three simulation runs, which are the same as our earlier studies for H‐ENA production processes (Wang et al, ). In the hybrid model, ions are treated as macroparticle clouds moving under the Lorentz force, while electrons are treated as a charge‐neutralizing fluid.…”

Section: Model Descriptionmentioning

confidence: 99%

“…The H‐ENA diagnostics allow remote imaging of the neutral density distribution and plasma flux distribution. At Mars, the H‐ENA imaging has revealed a deflection of solar wind protons at the subsolar point (Futaana, Barabash, Holmström, et al, ), a global asymmetry in the magnetosheath proton flow (Wang et al, , ), and oscillations of the magnetospheric plasma flow (Grigoriev et al, ). We will show in section that the precipitating H‐ENAs can be used to constrain the exospheric density of Mars and its annual variability.…”

Section: Introductionmentioning

confidence: 99%

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Precipitation of Hydrogen Energetic Neutral Atoms at the Upper Atmosphere of Mars

et al. 2018

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We study the properties of neutral hydrogen atoms precipitating onto the upper atmosphere of Mars. Energetic neutral atoms (ENAs) are produced by the charge exchange process between protons of solar wind (both upstream and shocked) as well as planetary origins and the Martian exospheric neutrals. Using a global hybrid plasma model for Mars-solar wind interaction combined with an up-to-date exosphere model of Mars, we calculate the fluxes, spatial distributions, energy spectra, and direction distributions of hydrogen ENAs (H-ENAs) at the Martian exobase for each source proton population. H-ENAs originating from the upstream solar wind region and the magnetosheath dominate the precipitation. Two percent of the solar wind flux penetrates through the magnetic barrier as H-ENAs under solar minimum conditions. The precipitating solar wind H-ENA flux is axially symmetric about Sun-Mars line, while the magnetosheath and planetary H-ENAs have higher fluxes and a more-extended precipitation area in the hemisphere where the convection electric field is pointing away from the planet, causing a significant precipitation beyond the terminator. The observed asymmetry is consistently explained by an asymmetric plasma flow in the dayside magnetosheath. The solar wind dynamic pressure increases the solar wind H-ENA precipitation normalized by the upstream proton flux, due to a closer bow shock position and thus a higher exospheric column density for charge exchange. The spatial distribution of the magnetosheath solar wind and planetary H-ENAs becomes more axially symmetric with increased dynamic pressure. The solar wind interaction with Mars exhibits more gas-dynamic-like signatures for higher dynamic pressure.

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Section: Simulation Results: Solar Wind H‐enasmentioning

confidence: 99%

Section: Model Descriptionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Precipitation of Hydrogen Energetic Neutral Atoms at the Upper Atmosphere of Mars

et al. 2018

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“…The ENA energy distribution is no longer beam-like but mirrors that of the shocked solar wind proton population present in the sheath (e.g., Kallio et al, 1997;Wang et al, 2016Wang et al, , 2018. The deflection and thermalization of solar wind protons in the sheath region mean that ENAs produced here move in ballistic trajectories that do not necessarily intersect the dayside atmosphere.…”

Section: Introductionmentioning

confidence: 92%

The Modulation of Solar Wind Hydrogen Deposition in the Martian Atmosphere by Foreshock Phenomena

et al. 2019

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The neutral exosphere of Mars extends far upstream beyond the bow shock, and as a result, solar wind protons can charge exchange with this neutral exosphere to produce energetic neutral atoms. Energetic neutral atoms produced directly upstream of Mars will precipitate into the Martian dayside atmosphere, where some fraction can undergo a charge stripping reaction and can be observed as “penetrating protons.” Clear, quasiperiodic modulations in penetrating proton densities are observed during certain Mars Atmosphere and Volatile EvolutioN (MAVEN) periapsis passes, and we show that these modulations occur during radial interplanetary magnetic field conditions. During such times, the region sunward of Mars is defined by quasi‐parallel shock conditions, generating foreshock structures characterized by enhancements in magnetic field strength, enhancements in proton density, and deceleration and deflection of the solar wind flow. These structures are observed at time cadences equal to the modulation of penetrating proton densities at periapsis. Particle tracing simulations show that the convection of these structures with the solar wind leads to localized enhancements in the rate of charge exchange upstream of the shock, producing the observed temporal variations in penetrating proton densities at periapsis. The observation of modulated penetrating proton densities at periapsis can thus be used to infer the existence of radial interplanetary magnetic field conditions upstream of the bow shock at Mars at times when MAVEN does not sample the upstream solar wind.

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“…These models have been used to understand an extensive array of Martian plasma processes and interactions. Plasma boundaries (Bertucci et al, ; Bößwetter et al, ; Najib et al, ), spatial ion distribution (Najib et al, ), ion escape (Brecht et al, ; Brecht & Ledvina, ; Dong, Fang et al, ; Fang et al, ; Kallio, Fedorov et al, ), magnetic topology (Liemohn et al, ), energetic neutral atoms (ENAs; Gunell et al, ; Kallio, Barabash et al, ; Wang et al, , ), solar wind alpha particles (Chanteur et al, ), and X‐ray emission (Gunell et al, ) have all been studied using Martian plasma models. Transient processes including coronal mass ejection (CMEs; Dong, Ma, et al, ; Ma et al, ), changes in dynamic pressure (Ma et al, ), changes in solar extreme ultraviolet (EUV) flux (Modolo et al, , ), seasonal variation (Dong et al, ), and crustal field rotation (Fang et al, ; Ma et al, ) have also been topics of study.…”

Section: Introductionmentioning

confidence: 99%

Comparison of Global Martian Plasma Models in the Context of MAVEN Observations

Egan

Dong

et al. 2018

JGR Space Physics

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Global models of the interaction of the solar wind with the Martian upper atmosphere have proved to be valuable tools for investigating both the escape to space of the Martian atmosphere and the physical processes controlling this complex interaction. The many models currently in use employ different physical assumptions, but it can be difficult to directly compare the effectiveness of the models since they are rarely run for the same input conditions. Here we present the results of a model comparison activity, where five global models (single-fluid MHD, multifluid MHD, multifluid electron pressure MHD, and two hybrid models) were run for identical conditions corresponding to a single orbit of observations from the Mars Atmosphere and Volatile EvolutioN (MAVEN) spacecraft. We find that low-altitude ion densities are very similar across all models and are comparable to MAVEN ion density measurements from periapsis. Plasma boundaries appear generally symmetric in all models and vary only slightly in extent. Despite these similarities there are clear morphological differences in ion behavior in other regions such as the tail and southern hemisphere. These differences are observable in ion escape loss maps and are necessary to understand in order to accurately use models in aiding our understanding of the Martian plasma environment.

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Emission of hydrogen energetic neutral atoms from the Martian subsolar magnetosheath

Cited by 12 publications

References 60 publications

Precipitation of Hydrogen Energetic Neutral Atoms at the Upper Atmosphere of Mars

Precipitation of Hydrogen Energetic Neutral Atoms at the Upper Atmosphere of Mars

The Modulation of Solar Wind Hydrogen Deposition in the Martian Atmosphere by Foreshock Phenomena

Comparison of Global Martian Plasma Models in the Context of MAVEN Observations

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