Detection of Mesospheric CO₂ Ice Clouds on Mars in Southern Summer

Abstract

This paper reports the first detections of two high‐altitude nighttime CO2 clouds on Mars during southern summer (Ls=264° and Ls=330°) with stellar occultation measurements by the Imaging Ultraviolet Spectrograph on board the Mars Atmosphere and Volatile Evolution spacecraft. Interpretation of the transmission spectra with Mie theory indicates particle radii of ∼90–110 nm assuming a monodisperse distribution. The altitude profile of extinction indicates that the cloud layers are confined horizontally to sizes less than ∼500–700 km. Examination of the CO2 density and temperature profiles reveals strong wave‐like perturbations. Supersaturated temperatures occur at the maximum negative extent of these wave‐like perturbations, which are organized in longitude with a dominant m=3 zonal harmonic. This suggests that tides are important in the formation of CO2 clouds.

First Detection and Thermal Characterization of Terminator CO2Ice Clouds With ExoMars/NOMAD

“…The first nighttime CO 2 ice clouds were observed at altitudes 80–110 km, at low to mid S latitudes and L S = 134–137° using UV stellar occultations by SPICAM on board Mars Express (MEx) (Montmessin et al., 2006). This is also the first case of simultaneous identification of CO 2 ice absorption and atmospheric temperature (also in Jiang et al., 2019), which unambiguously classified the observed absorption as CO 2 ice as opposed to water ice.…”

Troposphere-to-mesosphere microphysics of carbon dioxide ice clouds in a Mars Global Climate Model

“…Other climatologies have been published after these first discoveries: the Compact Reconnaissance Imaging Spectrometer for Mars (CRISM) instrument on MRO distinguished CO 2 ice clouds from water ice clouds by the absence of water ice absorption signatures (Vincendon et al, 2011) and the MCS instrument mapped high-altitude detached layers without definitive composition identification (Sefton-Nash et al, 2013). The latest additions to the climatologies come from the Imaging Ultraviolet Spectrograph (IUVS) instrument on the MAVEN mission that observed mesospheric detached layers at limb (Stevens et al, 2017) and two putative CO 2 ice clouds in stellar occultation (Jiang et al, 2019), from the Planetary Fourier Spectrometer (PFS) on MEX that measures the same 4.26 m CO 2 ice scattering peak as OMEGA (Aoki et al, 2018), and from CRISM/MRO limb profiles providing composition of mesospheric aerosols as well (Clancy et al, 2019).…”

Aerosols and Tides in the Martian Tropics During Southern Hemisphere Spring Equinox From Mars Climate Sounder Data

“…Thermal tides have also been detected in the thermosphere, with analysis of accelerometer data from the aerobraking phases of Mars Global Surveyor and Mars Odyssey revealing m = 2–3 patterns in density at altitudes of 100–160 km (Keating et al., 1998; Wang et al., 2006; Withers et al., 2003). More recently, Mars Atmosphere and Volatile EvolutioN (MAVEN) measurements have been used to detect m = 1–3 structures at altitudes of up to 190 km (England et al., 2016; Jiang et al., 2019; Lo et al., 2015; Stevens et al., 2017). MGS Radio Science measurements have revealed tidal effects up to altitudes of 200 km (Bougher et al., 2004; Cahoy et al., 2006), while Mars Reconnaissance Orbiter (MRO) radio tracking data have revealed m = 1–2 patterns in density in the exosphere, at ∼250 km (Mazarico et al., 2008).…”