Reference : The O(1S) 297.2 nm dayglow emission: a tracer of CO2 density variations in the Martia...
Scientific journals : Article
Physical, chemical, mathematical & earth Sciences : Space science, astronomy & astrophysics
http://hdl.handle.net/2268/230297
The O(1S) 297.2 nm dayglow emission: a tracer of CO2 density variations in the Martian lower thermosphere
English
Gkouvelis, Leonardos mailto [Université de Liège - ULiège > Département d'astrophys., géophysique et océanographie (AGO) > Labo de physique atmosphérique et planétaire (LPAP) >]
Gérard, Jean-Claude mailto [Université de Liège - ULiège > Département d'astrophys., géophysique et océanographie (AGO) > Département d'astrophys., géophysique et océanographie (AGO) >]
Ritter, Birgit mailto [Université de Liège - ULiège > Département d'astrophys., géophysique et océanographie (AGO) > Labo de physique atmosphérique et planétaire (LPAP) >]
Hubert, Benoît mailto [Université de Liège - ULiège > Département d'astrophys., géophysique et océanographie (AGO) > Labo de physique atmosphérique et planétaire (LPAP) >]
Schneider, Nicholas []
Jain, Sonal []
Nov-2018
Journal of Geophysical Research. Planets
Wiley
123
Yes (verified by ORBi)
International
2169-9097
2169-9100
Hoboken
NJ
[en] Mars ; dayglow ; ultraviolet ; carbon dioxide ; photochemistry ; quantum yield
[en] The O(1S) metastable atoms can radiatively relax by emitting airglow at 557.7 and 297.2 nm. The
latter one has been observed with the Imaging Ultraviolet Spectrograph onboard the Mars Atmosphere and Volatile Evolution Mars orbiter since 2014. Limb profiles of the 297.2-nm dayglow have been collected near periapsis with a spatial resolution of 5 km or less. They show a double-peak structure that was previously predicted but never observed during earlier Mars missions. The production of both 297.2-nm layers is dominated by photodissociation of CO2. Their altitude and brightness is variable with season and latitude, reflecting changes in the total column of CO2 present in the lower thermosphere. Since the lower emission peak near 85 km is solely produced by photodissociation, its peak is an indicator of the unit optical depth pressure level and the overlying CO2 column density. Its intensity is directly controlled by the Lyman-α solar flux reaching the Martian upper atmosphere. We take advantage of the Lyman-α flux measurements of the solar Extreme Ultraviolet Monitor instrument onboard Mars Atmosphere and Volatile Evolution to model
the observed OI 297.2-nm limb profiles. For this, we combine photodissociation sources with chemical processes and photoelectron impact excitation. To determine the relative importance of the excitation processes, we apply the model to the atmospheric structure measured by the Viking 1 lander before applying it to a model atmosphere. We find very good agreement with the lower peak structure and intensity if the CO2 density provided by the Mars Climate Database is scaled down by a factor between 0.50 and 0.66. We also determine that the previously uncertain quantum yield for production of O(1S) atoms by photodissociation of CO2 at Lyman-α wavelength is about 8%.
Space sciences, Technologies and Astrophysics Research - STAR
PRODEX - BELSPO
Researchers ; Professionals
http://hdl.handle.net/2268/230297
10.1029/2018JE005709
We analyze the altitude distribution of the oxygen emission at 297.2 nm observed in the Martian dayside atmosphere with the Imaging Ultraviolet Spectrograph onboard the Mars Atmosphere and Volatile Evolution orbiter. This emission is mostly produced by the interaction of solar ultraviolet radiation with the CO2-dominated atmosphere above 60 km. We show that this emission has two intensity peaks. The altitude of the lower one is entirely controlled by the amount of carbon dioxide crossed by the bright solar Lyman-alpha line. We determine what fraction of CO2 dissociation leads to the 297.2-nm emission and derive a relationship between the altitude of the maximum brightness and its pressure level. Comparisons with the predictions of the Mars Climate Model indicate that this model overestimates the amount of carbon dioxide in the 65–85-km region by a factor of about 2. Global monitoring
and accurate modeling of the atmospheric pressure in this region of the atmosphere and its seasonal and
latitudinal variations are important to understand the large-scale dynamics and for future space missions.
Our results provide a method to constrain the Martian atmospheric structure in a region that is largely
unexplored by other experimental methods.

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