Characterisation of deposited dust particles on Mars insight lander Instrument Context Camera (ICC) lens

The ubiquitous dust in the Martian environment plays a key role in its weather and climate: it must be taken into account in the interpretation of remote sensing data and observations, and could pose a potential risk to surface equipment and operations. In this study, we use observations retrieved by the Instrument Context Camera (ICC) onboard the InSight lander to evaluate the accumulation of dust on the camera lens and estimate the size of the deposited dust particles. Dust contamination is revealed as mottled pattern image artefacts on ICC observations. These were detected using a template matching blob detection algorithm and modelled with a first-order optical model to simulate their size and optical density as a function of the particle diameter. The results show a deep decay in the first 70 sols (LS = 295–337°, MY34) during which dust particles deposited at landing were mostly removed. The subsequent gradual decrease and stable behaviour in the number of detected particles is only interrupted by accumulation and removal periods around sols 160 (LS ∼ 23°, MY35) and 800–1100 (LS = 9–150°, MY36). The estimated particle sizes follow a similar trend, with deposited particles due to wind-driven forces (average diameter < 50 μm) being smaller than the ones deposited by other forces during landing, with particles of up to 220 μm of diameter. The results of this study provide an additional source of information for evaluating aeolian dust processes in Mars, with quantitative results on dust accumulation and removal activity, and may contribute to a better determination of dust entrainment threshold models by constraining susceptible dust particle sizes.