Nature Geoscience (2024) https://doi.org/10.1038/s41561-024-01457-7
A. Valantinas, N. Thomas, A. Pommerol, O. Karatekin, L. Ruiz Lozano, C. B. Senel, O. Temel, E. Hauber, D. Tirsch, V. T. Bickel, G. Munaretto, M. Pajola, F. Oliva, F. Schmidt, I. Thomas, A. S. McEwen, M. Almeida, M. Read, V. G. Rangarajan, M. R. El-Maarry, C. Re, F. G. Carrozzo, E. D’Aversa, F. Daerden, B. Ristic, M. R. Patel, G. Bellucci, J. J. Lopez-Moreno, A. C. Vandaele & G. Cremonese
The present-day water cycle on Mars has implications for habitability and future human exploration. Water ice clouds and water vapour have been detected above the Tharsis volcanic province, suggesting the active exchange of water between regolith and atmosphere. Here we report observational evidence for extensive transient morning frost deposits on the calderas of the Tharsis volcanoes (Olympus, Arsia and Ascraeus Montes, and Ceraunius Tholus) using high-resolution colour images from the Colour and Stereo Surface Imaging System on board the European Space Agency’s Trace Gas Orbiter. The transient bluish deposits appear on the caldera floor and rim in the morning during the colder Martian seasons but are not present by afternoon. The presence of water frost is supported by spectral observations, as well as independent imagery from the European Space Agency’s Mars Express orbiter. Climate model simulations further suggest that early-morning surface temperatures at the high altitudes of the volcano calderas are sufficiently low to support the daily condensation of water—but not CO2—frost. Given the unlikely seasonal nature of volcanic outgassing, we suggest the observed frost is atmospheric in origin, implying the role of microclimate in local frost formation and a contribution to the broader Mars water cycle.
a, Global view of Mars with white box marking the location of Olympus Mons. b, HRSC wide-angle image of Olympus Mons acquired in the early morning (LST = 7:20, Ls = 346.7°, latitude = 18.2° N, longitude = −133.2° E). The black dashed line indicates the orbit of the TGO corresponding to the images in d and e. The white box highlights the close up in c. c, Zoomed-in view of the Olympus Mons caldera. The white and blue dashed rectangles show the footprints of the CaSSIS and NOMAD-LNO observations, respectively. d, High-resolution (4.5 m pixel–1) CaSSIS colour image of frost on the caldera floor and northern rim of Olympus Mons (LST = 7:11, Ls = 344.1°). Frost is absent on the well-lit steep slopes. The blue rectangle marks the footprint of the one NOMAD-LNO observation that falls within the frost-covered area. e, NOMAD-LNO channel observation of the Olympus Mons caldera. The ice index values indicate the presence of frost over the caldera floor (>µ + 3σ). The coloured areas on the plot indicate the confidence intervals. HRSC image ID: hn889_0000 (b,c). CaSSIS colour image ID: MY36_022332_162_0_NPB (d). NOMAD-LNO observation ID: 20221125_082524 (e). Credit: b, ESA/DLR/FU Berlin; d, ESA/TGO/CaSSIS under a Creative Commons license CC-BY-SA 3.0 IGO.
