Early morning frost has been detected on some of the largest mountains in the solar system—the colossal Martian volcanoes near the planet’s equator, which rise up to three times the height of Mount Everest. This frost, which forms overnight during colder months, is thinner than a human hair and appears in the summit craters and on sections of the rims of these volcanic giants. It then evaporates a few hours after sunrise.
Despite its exceptional thinness, this frosty layer covers an enormous area. Scientists have calculated that in the colder Martian seasons, about 150,000 tonnes of water, equivalent to 60 Olympic swimming pools, condense daily on the summits of these towering mountains. Adomas Valantinas, a planetary scientist at the University of Berne in Switzerland and Brown University in the US, emphasized the significance of this discovery, stating, “It’s the first time we’ve discovered water frost on the volcano summits and the first time we’ve discovered water frost in the equatorial regions of Mars.”
Previous missions have provided evidence of frozen and liquid water on Mars, particularly at the polar regions. The landscape patterns suggest that Mars was once a much wetter and potentially habitable world, with vast lakes and meandering rivers. The frost-tipped volcanoes may offer a glimpse into a past Martian climate, indicating atmospheric processes from millions of years ago.
Valantinas and his colleagues discovered the frost using high-resolution color images taken by the European Space Agency’s Trace Gas Orbiter (TGO) during the early morning hours on Mars. They confirmed the presence of frost using a spectrometer on TGO and additional images from the Mars Express orbiter. The frost, appearing as a bluish hue on the caldera floors, is absent from well-lit slopes.
The Tharsis region on Mars is a vast volcanic plateau near the planet’s equator, home to numerous large volcanoes, including Pavonis Mons and Olympus Mons. The latter, nearly 16 miles tall, is almost three times the height of Everest and covers an area the size of France. Given the high daytime temperatures and the thin Martian atmosphere, scientists previously thought it unlikely for frost to form on these volcanic peaks.
However, in a study published in Nature Geoscience, researchers describe how Martian winds may transport moist air up the mountainsides into the calderas, where it condenses and settles as frost. Modeling suggests that this frost is composed of water ice, as the peaks are not cold enough for carbon dioxide frost to form.
John Bridges, a professor of planetary sciences at the University of Leicester, highlighted the ongoing success of the TGO mission and its Colour and Stereo Surface Imaging System (CaSSIS) camera. Understanding Mars’s present-day water cycle, both in the atmosphere and near the surface, will be crucial for future exploration missions, including human missions where water will be an essential in situ resource.
The discovery of early morning frost on Martian volcanoes not only enriches our understanding of Mars’s current climate but also provides insights into its climatic history, which could inform future explorations and the search for life on the red planet.