Journal article
Characterizing Precipitation Behaviors of H− in the Martian Atmosphere
Journal of geophysical research. Space physics, Vol.129(4), e2024JA032420
04/2024
DOI: 10.1029/2024JA032420
Appears in UI Libraries Support Open Access
Abstract
Solar wind protons can charge exchange with the extensive hydrogen corona of Mars, resulting in a significant flux of energetic neutral atoms (ENAs). As these solar wind hydrogen ENAs precipitate into the upper atmosphere, they can experience electron attachment or detachment, resulting in populations of H− and H+, respectively, with upstream velocity. We seek to characterize the behavior of H− in the ionosphere of Mars through a combination of in situ data analysis and mathematical models. Observations indicate that measurable H− precipitation in the ionosphere of Mars is rare, occurring during only 1.8% of available observations. These events occur primarily during high energy solar wind conditions near perihelion. We also compare H− fluxes to those of H+ and find that H− fluxes are ∼4.5 times less than H+, indicating preferential conversion of hydrogen ENAs to H+. We develop a simple model describing the evolution of the charged and neutral fraction of ENAs and H− ions versus altitude. We find that 0.29%–0.78% of ENAs are converted to H− for solar wind energies 1–3 keV. We also predict that the effects of photodetachment on the H‐H− system are non‐negligible.
Plain Language Summary
As the solar wind propagates throughout the solar system, it can directly interact with the atmosphere of Mars. Protons in the solar wind can obtain an electron from hydrogen in the planet's large atmosphere, resulting in a population of energetic neutral hydrogen atoms (ENAs). These ENAs bypass electromagnetic boundaries, penetrating into the collisional CO2 component of the Martian atmosphere. Through interactions with CO2, these ENAs can obtain or lose an electron, generating populations of H− and H+. We find that observing measurable amounts of H− at Mars is rather difficult. These ions are best observed during high energy solar wind conditions during Mars's closest approach to the Sun. We also find that hydrogen ENAs are more often converted to H+ than H−. We also develop a simple mathematical model describing how many ENAs are converted to H−. We find that in addition to collisional interactions with CO2, interactions between solar radiation and H− are non‐negligible. We determine that a minute fraction of ENAs are converted to H−.
Key Points
H− precipitation events at Mars occur primarily during high energy solar wind events during perihelion
H− fluxes are on average 4.5 times less than those of H+, indicating preferential conversion of energetic neutral atoms to H+
Effects of photodetachment on H− are notable at ionospheric altitudes above 125 km
Details
- Title: Subtitle
- Characterizing Precipitation Behaviors of H− in the Martian Atmosphere
- Creators
- Sarah Henderson - University of IowaJasper Halekas - University of IowaRebecca Jolitz - University of California, BerkeleyDavid Mitchell - University of California, BerkeleyChristian Mazelle - Université de ToulouseFrank Eparvier - University of Colorado BoulderMeredith Elrod - Goddard Space Flight Center
- Resource Type
- Journal article
- Publication Details
- Journal of geophysical research. Space physics, Vol.129(4), e2024JA032420
- Publisher
- Wiley
- DOI
- 10.1029/2024JA032420
- ISSN
- 2169-9380
- eISSN
- 2169-9402
- Number of pages
- 19
- Grant note
- MAVEN contract (NNH10CC04C)
- Language
- English
- Date published
- 04/2024
- Academic Unit
- Physics and Astronomy
- Record Identifier
- 9984618626802771
Metrics
1 Record Views