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

Holmström, M.; Alho, Markku; Järvinen, R.; Kallio, Esa; Barabash, S.; Futaana, Yoshifumi

doi:10.1029/2018ja025188

Cited by 17 publications

(57 citation statements)

References 61 publications

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“…The simulation thus assumes that all precipitating ENAs are produced upstream of the bow shock and ignores ENAs produced in the magnetosheath. The foreshock structures observed in this study are characterized by large enhancements in density, making them analogous to the high dynamic pressure case in the Wang et al (2018) study, supporting our assumption that ENAs produced upstream of the bow shock are the primary source of precipitating ENAs. Protons are observed below and above the beam energy in this panel (between ∼50 and 200 eV and between ∼600 and 1,000 eV), which may well be sourced from the magnetosheath.…”

Section: Simulations Of Charge Exchange In the Upstream Regionsupporting

confidence: 85%

“…Their simulation results showed that as the solar wind dynamic pressure increased, ENAs sourced from upstream of the bow shock became the more important precipitation source. The foreshock structures observed in this study are characterized by large enhancements in density, making them analogous to the high dynamic pressure case in the Wang et al (2018) study, supporting our assumption that ENAs produced upstream of the bow shock are the primary source of precipitating ENAs. Finally, the aforementioned hybrid modeling was carried out under Parker Spiral-like IMF conditions, as apposed to the radial IMF conditions present in our case study.…”

Section: Simulations Of Charge Exchange In the Upstream Regionsupporting

confidence: 85%

“…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%

“…ENAs produced upstream of the bow shock and in the magnetosheath that precipitate into the dayside atmosphere will undergo collisional interactions with the neutral constituents, including energy deposition, angular spreading, and back scattering (Kallio et al, 1997;Wang et al, 2018). Monte Carlo modeling by Kallio and Barabash (2001) showed that energy deposition by these ENAs peaks between 120-and 130-km altitude in the Martian atmosphere.…”

Section: Introductionmentioning

confidence: 99%

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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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Section: Simulations Of Charge Exchange In the Upstream Regionsupporting

confidence: 85%

Section: Simulations Of Charge Exchange In the Upstream Regionsupporting

confidence: 85%

Section: Introductionmentioning

confidence: 92%

Section: Introductionmentioning

confidence: 99%

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

et al. 2019

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“…Measurements of the H + /H-ENA flux ratio at the top of the Monte Carlo model have not been discussed so far in the literature. In a recent study, Wang et al (2018) have modeled the properties of H atoms precipitation into the atmosphere using a global hybrid plasma model. They find that the value of the H + /H-ENA ratio at the upper boundary in their model rapidly drops from over 100 beyond 1600 km to ∼1 near 600 km (X.D.…”

Section: Discussionmentioning

confidence: 99%

Lyman-α emission in the Martian proton aurora: Line profile and role of horizontal induced magnetic field

Gérard

Hubert

Ritter

et al. 2019

Icarus

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Enhancements of the dayside Lyman-α emission by as much as ∼50% have been observed between 120 and 130 km in the lower Martian thermosphere from the Mars Express and MAVEN satellites, usually following solar events such as coronal mass ejections and corotating interaction regions. They have been assumed to be optical signatures of proton aurora related to an increase in the solar wind proton flux hitting Mars' bow shock. We present model simulations of the Lyman-α line profiles at different altitudes. These are partly guided by in situ measurements of the energy spectrum of protons in the magnetosheath region by the SWIA instrument on board the MAVEN spacecraft. We show that the auroral Lyman-α line profile is significantly broader than the hydrogen core of the planetary thermal H atom. Consequently, most of the auroral emission is produced outside the optically thick hydrogen core and creates the observed intensity enhancement. Simulations with incident energetic hydrogen atoms (H ENAs) produce a somewhat broader line profile. Monte Carlo calculations are made separately for incident solar wind protons and H ENAs produced by charge exchange in the hydrogen corona. Absorption by CO 2 along the line of sight significantly affects the intensity distribution in the lower thermosphere. The calculated altitude of the peak emission for both types of incident particles is consistent with the observed characteristics of the proton aurora. We show that the presence of a horizontal induced magnetic field somewhat increases the line width and decreases the altitude of the emission peak as a consequence of the magnetic barrier effect on proton precipitation. The brightness of the Lyman-α emission also drops as a result of increased magnetic shielding of the protons.

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Energy Spectral Properties of Hydrogen Energetic Neutral Atoms Emitted From the Dayside Atmosphere of Mars

et al. 2019

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Key Points: We use two-segment power laws to fit the energy spectra of sunward-flowing hydrogen energetic neutral atoms (HENA) observed at Mars. Observed HENAs have higher fluxes and more high-energy component than the modeled backscattered HENAs. The more high-energy component implies additional sources of sunward HENAs, most likely the charge-exchange HENAs in the shocked solar wind. AbstractThe energy spectrum of hydrogen energetic neutral atoms (HENA) emitted from the dayside atmosphere of Mars reveals the physical processes of their origin and provides means for remote-sensing on the Mars plasma environment. We first compile all available energy spectra of sun-ward flowing HENA using high energy resolution data from the Neutral Particle Detectors on Mars Express from February to June 2004. The median value of the HENA directional flux is 1.12×10 5 cm -2 s -1 sr -1 from 0.3 to 5 keV, making Mars a bright source of HENAs. The energy spectra of the measured HENAs can be approximated by a two-segment power-law spectra. Then we compared the measured statistical energy spectra with those from a kinetic particle transport code. The comparison indicates that the measured HENA energy spectrum is harder (more high-energy components) than the modeled backscattered HENAs. We propose that a population of sunward-flowing, charge-exchanged HENAs produced in the dayside magnetosheath is the most probable reason for this difference. This HENA population with unexpected energy spectrum highlights the kinetic nature of the dayside magnetosheath of Mars. Plain Language SummaryWe study the measurements of fast hydrogen atoms moving towards the Sun from the dayside upper atmosphere of Mars. These measurements were done by the Neutral Particle Detectors on Mars Express spacecraft from February to June in 2004. We have got a curve showing how many H atoms move within a certain speed range. This so-called energy spectrum can tell us where these atoms come from and what has happened to them. Previous studies thought these H atoms are originally protons in the solar wind and are neutralized and scattered by the molecules high in Martian atmosphere. Our study, with the help of computer simulations, shows that the origin is correct, whereas scattering is not enough to explain the observed energy spectrum. We think that the H atoms we detected also contain those from solar wind protons that are deflected by the magnetic field around Mars. This study reveals more insight on how Mars atmosphere reacts to the supersonic solar wind and is related to the bigger question: how did Mars lose most of its atmosphere and water?

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

Cited by 17 publications

References 61 publications

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

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

Lyman-α emission in the Martian proton aurora: Line profile and role of horizontal induced magnetic field

Energy Spectral Properties of Hydrogen Energetic Neutral Atoms Emitted From the Dayside Atmosphere of Mars

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