https://doi.org/10.1029/2021GL095895

Giuliano Liuzzi, Geronimo L. Villanueva, Loïc Trompet,Matteo M. J. Crismani,Arianna Piccialli,Shohei Aoki,Miguel Angel Lopez-Valverde,Aurélien Stolzenbach,Frank Daerden,Lori Neary,Michael D. Smith,Manish R. Patel,Stephen R. Lewis,R. Todd Clancy,Ian R. Thomas,Bojan Ristic,Giancarlo Bellucci,Jose-Juan Lopez-Moreno, Ann Carine Vandaele

We present observations of terminator CO₂ ice clouds events in three groups: Equatorial dawn, Equatorial dusk (both between 20°S and 20°N) and Southern midlatitudes at dawn (45°S and 55°S east of Hellas Basin) with ESA ExoMars Trace Gas Orbiter's Nadir and Occultation for MArs Discovery instrument. CO₂ ice abundance is retrieved simultaneously with water ice, dust, and particle sizes, and rotational temperature and CO₂ column profiles in 16 of 26 cases. Small particles (<0.5 μm) prevail at dusk, while water ice likely provides most source nuclei at dawn. Clouds east of Hellas are found to be dominantly nucleated on surface-lifted dust. CO₂ ice is sometimes detected in unsaturated air together with dust nuclei at dawn, suggesting ongoing sublimation. Depending on latitude and local time, the interplay between particle precipitation and the lifetime of temperature minima (i.e., cold pockets) determines CO₂ ice properties.

(a) Summary of the detections in the Equatorial region at dusk, dawn (b) and in the Hellas region at dawn (c). The plots report only the cases in which temperature (and CO₂ saturation ratio, contours) is retrieved together with the properties of dust (orange dots), CO₂ ice (white) and water ice (blue).