Abnormal Dawn-Dusk Asymmetry of Protonated Ions in the Martian Ionosphere

Normally, the Martian ionosphere displays a dusk enhancement due to continuous depletion of plasma via recombination during day-to-night transport. Using the extensive measurements made by the Neutral Gas and Ion Mass Spectrometer on board the Mars Atmosphere and Volatile Evolution spacecraft, we sh...

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Bibliographic Details
Published in:Astrophysical journal. Letters 2020-06, Vol.895 (2), p.L43
Main Authors: Cui, J., Z.-P., Ren, Z.-P., Wu, X.-S., Wu, Y.-Q., Hao, Wei, Y.
Format: Article
Language:English
Subjects:
Aeronomy
Atmosphere
Atmospheric composition
Atmospheric science
Atmospheric variability
Climatic evolution
Corona
Depletion
Diurnal variations
Evolution
Hydrogen
Inner planets
Ionosphere
Mars
Mars atmosphere
Mars climate
Mass spectrometry
Neutral gases
Photodissociation
Planetary atmospheres
Planetary ionospheres
Planetary science
Solar system
Solar system astronomy
Solar system planets
Spacecraft
Titan
Upper atmosphere
Venus
Venus atmosphere
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Summary:Normally, the Martian ionosphere displays a dusk enhancement due to continuous depletion of plasma via recombination during day-to-night transport. Using the extensive measurements made by the Neutral Gas and Ion Mass Spectrometer on board the Mars Atmosphere and Volatile Evolution spacecraft, we show that several species, including , OH+, H2O+, and NH+, present instead an abnormal dawn enhancement above the exobase where they are mainly produced by ion-neutral reactions involving H2. Such a peculiarity is indicative of a dawn bulge of H2 present in the Martian upper atmosphere and corona, which is driven by subsidence in regions of horizontal wind convergence and the subsequent buildup of minor atmospheric species with large vertical scale heights. A similar dynamical process is also known to occur in the upper atmospheres of other solar system bodies such as the Earth, Venus, and Titan. Interestingly, despite that the diurnal variations of O and N are subject to the same dynamical effect, a dawn enhancement is not seen for O+ and N+, possibly due to the nonthermal production of their parent atoms in the ambient atmosphere via processes such as photodissociation and dissociative recombination. The H2 distribution inferred in this study is important for a thorough understanding of hydrogen escape and climate evolution on Mars.
ISSN:2041-8205
2041-8213
DOI:10.3847/2041-8213/ab930c