Effect of the 2018 Martian Global Dust Storm on the CO₂ Density in the Lower Nightside Thermosphere Observed From MAVEN/IUVS Lyman‐Alpha Absorption

Abstract

The MAVEN/Imaging Ultraviolet Spectrograph (IUVS) instrument measures Lyman-α emissions from interplanetary and Martian hydrogen at the limb and through the extended corona of Mars. In June 2018, a global dust storm (GDS) surrounded Mars for a few months, heating the lower atmosphere and leading to an expansion of the Martian atmosphere. Nightside IUVS observations before and throughout this GDS showed the altitude of CO 2 absorption of Lyman-α photons in the thermosphere to increase by 4.5±1.0 km on 8 June 2018. This shift is attributed to an increase of the CO 2 density by a factor 1.9±0.2 at 110 km due to the heating of the lower atmosphere. These nightside observations, not previously used to study dust storms, in an altitude range not sampled by other instruments, are consistent with dayside MAVEN observations and allow for more comprehensive determination of the global changes produced by the GDS on the Martian thermosphere.

Species‐dependent Response of the Martian Ionosphere to the 2018 Global Dust Event

“…The response of the Martian upper atmosphere during the same GDS has also been reported by Chaufray et al. (2020) using the MAVEN Imaging Ultraviolet Spectrograph (Gröller et al., 2015, 2018) observations, revealing an increase in CO 2 density by a factor of ∼ 2 at 110 km due to the heating of the lower atmosphere. Important consequences of the dust storms also include the rise of the mesospheric and thermospheric water content (e.g., Heavens et al., 2011; Stone et al., 2020; Vandaele et al., 2019; Z. Wu et al., 2020), the enhancement of hydrogen escape (e.g., Chaffin et al., 2014; Heavens et al., 2018), as well as the elevation of the exobase altitude (e.g., Fu et al., 2020).…”

“…Over the same period, an opposite trend of density variation is observed for most species such as CO 2 , N 2 , CO, and Ar, with their densities maximized near L s ≈ 175°, consistent with the known diurnal variation of the Martian thermosphere (e.g., González-Galindo et al, 2009). Superposed on the above trends is a remarkable change in neutral density starting at L s ≈ 190°, nearly coincident with the onset of the 2018 GDS (e.g., Chaufray et al, 2020). This is manifested as a clear density enhancement for all species except for O and He as two exceptions whose density variations instead display a pronounced reduction during the GDS.…”

“…Superposed on the above trends is a remarkable change in neutral density starting at L s ≈ 190°, nearly coincident with the onset of the 2018 GDS (e.g., Chaufray et al., 2020). This is manifested as a clear density enhancement for all species except for O and He as two exceptions whose density variations instead display a pronounced reduction during the GDS.…”

Studies of the 2018/Mars Year 34 Planet‐Encircling Dust Storm

“…In the upper atmosphere, MAVEN was able to also measure how the bulk composition of the atmosphere changed in response to the storm. As stated above, the thermosphere warmed and expanded during the storm, leading to higher atmospheric densities (Chaufray et al., 2020). In conjunction, CO 2 and Ar densities increased in the thermosphere, but surprisingly, atomic O density decreased by 20% (Elrod et al., 2020).…”

“…Heating and expansion of the neutral martian atmosphere was also observed. This was manifested in a near‐doubling of CO 2 density on the planet's nightside at thermospheric altitudes (110 km) seen by MAVEN (Chaufray et al., 2020). MAVEN observed a near 20 K temperature increase in the thermosphere, while also seeing cooling at equatorial latitudes near the start of the storm due to adiabatic cooling in strong upward motion (Jain et al., 2020).…”