Impact of meteoric smoke particles on mesospheric water ice clouds on Mars

The thermal structure and water cycle in the lower atmosphere of Mars are thought to be controlled by dust particles supplied from the surface, acting as cloud condensation nuclei (CCN) for water ice clouds. However, the presence of water ice clouds in the mesosphere (Bernal et al., 2021) suggests that additional CCN sources may be required. Meteoric smoke particles (MSPs) are thought to be these sources, which are composed of carbonates formed by the reaction of atmospheric molecules with metal atoms ablated from meteoroids as they enter the atmosphere (Plane et al., 2018).

Due to their small size and difficulty in observing them, the distribution and function of MSPs as CCN remain unclear. Previous model studies have investigated cloud formation associated with MSPs (Hartwick et al., 2019). However, due to computational constraints in the GCM, these studies assumed that MSPs are supplied only from the upper boundary of the model, located at approximately 60 km altitude. As a result, they could not explicitly represent the 60–100 km altitude region, where meteoric metal ablation and subsequent chemical reactions responsible for MSP formation are expected to occur.

Here we focus on meteoric Mg species commonly observed in the Martian atmosphere (Crismani et al., 2023) and investigate their role in mesospheric cloud formation using two 1-D models: a photochemical model, PROTEUS (Nakamura et al., 2023), to evaluate the formation process of MSPs, and a cloud microphysics model, SPECK (Karyu et al., 2025), to track the evolution of the particle size distribution.

Clouds formed when CCN was supplied according to the altitude distribution of carbonates calculated by PROTEUS, but no clouds formed when CCN was supplied only from the upper boundary at an altitude of 200 km. This implies that nm-sized MSPs are not subject to sedimentation effects and that it is important to track the chemical reactions involved in the formation of MSPs.

These results support MSPs as effective condensation nuclei for Martian mesospheric water ice clouds and provide a quantitative link between meteoric metal chemistry and cloud microphysics.