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MAVEN‐IUVS Observations of the CO 2 + UV Doublet and CO Cameron Bands in the Martian Thermosphere: Aeronomy, Seasonal, and Latitudinal Distribution
Author(s) -
Gérard J.C.,
Gkouvelis L.,
Ritter B.,
Hubert B.,
Jain S. K.,
Schneider N. M.
Publication year - 2019
Publication title -
journal of geophysical research: space physics
Language(s) - English
Resource type - Journals
eISSN - 2169-9402
pISSN - 2169-9380
DOI - 10.1029/2019ja026596
Subject(s) - thermosphere , martian , aeronomy , mars exploration program , atmosphere of mars , atmospheric sciences , extreme ultraviolet , altitude (triangle) , atmosphere (unit) , spectrograph , environmental science , physics , flux (metallurgy) , ionosphere , spectral line , astrobiology , meteorology , astronomy , materials science , laser , geometry , mathematics , optics , metallurgy
We analyze two Martian years of dayglow measurements of the CO Cameron bands and the CO 2 + ultraviolet doublet (UVD) at 298–299 nm with the Imaging UltraViolet Spectrograph on board the Mars Atmosphere and Volatile EvolutioN (MAVEN) orbiter. We show that the altitude and the brightness of the two emissions peaks are strongly correlated, although data were collected over a wide range of latitudes and seasons. Averaged limb profiles are presented and compared with numerical simulations based on updated calculations of the production of the CO (a 3 Π) and the CO 2 + (B 2 Σ) states. The model simulations use the solar flux directly measured on board MAVEN with the Extreme Ultraviolet Monitor and the neutral densities provided by the Mars Climate Database version 5.3, adapted to the conditions of the observations. We show that the altitude and the shape of the sample limb profiles are well reproduced using the Mars Climate Database neutral atmosphere. The simulated peak intensities of the CO 2 + UVD and Cameron bands are in good agreement considering the uncertainties on the excitation cross sections and the calibration of the Imaging Ultraviolet Spectrograph (IUVS) and Extreme Ultraviolet Monitor instruments. No significant adjustment of the electron impact cross section on CO 2 to produce the a 3 Π state is needed. Seasonal‐latitudinal maps of the Cameron and UVD peak altitude observed during two Martian years show variations as large as 23 km. Model simulations of the amplitude of these changes are in fair agreement with the observations except during the southern summer dust period ( L s = 270–320°) when the calculated rise of the dayglow layer is underestimated.