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A Long Term Study of Mars Mesospheric Clouds Seen at Twilight Based on Mars Express VMC Images

M. V. Cardaci, J. Hernández-Bernal, A. Sánchez-Lavega, T. del Río-Gaztelurrutia, R. Hueso, E. Ravanis, A. Cardesín-Moinelo, S. Wood, D. Titov

We present the first systematic study of clouds observed during twilight on Mars. We analyze images obtained by the Visual Monitoring Camera on Mars Express between 2007 and 2020. Using an automated retrieval algorithm, we found 407 cases of clouds observed at twilight, in which the geometry of the observations allows to derive the minimum altitude, revealing that many of these clouds are in the mesosphere (above 40 km and up to 90 km). The majority of these mesospheric clouds were detected in mid latitudes at local autumn and winter, a new trend only hinted at by previous studies. In particular, we find a massive concentration of clouds in the southern mid latitudes between Terra Cimmeria and Aonia, a region where high altitude events have been previously observed. We propose that there is an unknown mechanism in these regions that enhances the probability to host high altitude clouds around the southern winter solstice.

Mars; Mars mesospheric clouds; Mars twilight; VMC; Astrophysics - Earth and Planetary Astrophysics

Geophysical Research Letters
Volume 48, Number 7
2021 March

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Faculdade de Ciências da Universidade de Lisboa Universidade do Porto Faculdade de Ciências e Tecnologia da Universidade de Coimbra
Fundação para a Ciência e a Tecnologia COMPETE 2020 PORTUGAL 2020 União Europeia