Effect of the 2018 Martian global dust storm on the CO2 density in the lower nightside thermosphere observed from MAVEN/IUVS Lyman-alpha absorption
Résumé
The planetary upper atmosphere is the region where most of the solar photons in the far and extreme UV are
absorbed and provide heating and ionization of the neutral atmosphere. The use of this absorption during stellar or
solar occultation is a standard method to identify species or derive information on the density and temperature of
the upper atmosphere. The UV emissions of the interplanetary hydrogen, and of the extended planetary hydrogen
coronae can also be absorbed by the planetary upper atmosphere and therefore be used to study the density of
the planetary upper atmosphere. This method was used for example by the Mars Express mission to study the
seasonal variations of the CO2 density in the Martian upper atmosphere.
In June 2018, an intense global dust storm surrounded Mars for a few months, heating the lower atmosphere
and leading to an expansion of the Martian atmosphere of few kilometers in the thermosphere. The Imaging
Ultraviolet Spectrograph (IUVS) on the Mars Atmosphere and Volatile EvolutioN (MAVEN) mission measured
the Lyman-α emission line from the interplanetary hydrogen and from the extended hydrogen corona of Mars at
the limb before and throughout this Planet Encircling Dust Event (PEDE). In the nightside IUVS observations,
the CO2 absorption of the Lyman-α photons is seen in the lower thermosphere near 110 km. An increase in the
altitude of the absorption was observed on 8 June 2018. This altitude shift is attributed to an increase of the CO2
density due heating of the lower atmosphere during the large dust storm at the surface of Mars.
In this presentation we will present these observations and the CO2 density variations, at a given altitude. Results
from this analysis are compared to other observations of the Martian upper atmosphere obtained at the dayside