The frost was detected 13.5 miles above Mars’ surface, making it the first time scientists have observed frozen water so close to the planet’s equator. This finding challenges previous assumptions that frost formation around the Martian equator was impossible due to the planet’s thin atmosphere and intense sunlight.
Perspective view of Olympus Mons from Mars Express, with frost (blue) in the cauldron-like hollow (Image credit: European Space Agency)
“We thought it was impossible for frost to form around Mars’s equator, as the mix of sunshine and thin atmosphere keeps temperatures relatively high at both surface and mountaintop – unlike what we see on Earth, where you might expect to see frosty peaks,” said lead author Adomas Valantinas, who made the discovery as a PhD student at the University of Bern, Switzerland, and is now a postdoctoral researcher at Brown University, USA. “Its existence here is exciting, and hints that there are exceptional processes at play that are allowing frost to form.”
Valantinas and his team spent five years analyzing data from the European Space Agency’s Trace Gas Orbiter (TGO) and Mars Express Orbiter, meticulously studying over 30,000 images of the region. Their research uncovered that during the Martian winter months, a delicate layer of frost, as thin as a human hair and likely only one-hundredth of a millimeter thick, forms on the peaks of Olympus Mons and other volcanoes in the Tharsis region. This frost, although thin, covers a vast area and contains an estimated 150,000 tonnes of water—equivalent to roughly 60 Olympic swimming pools—which briefly transfers between the surface and atmosphere each day during the cold seasons before evaporating under the Martian sun.
The frost’s formation is attributed to unique microclimates created by air circulation around the mountain summits and through the calderas, which are the collapsed craters formed by massive volcanic eruptions millions of years ago. These conditions allow the air to cool enough for frost to form, albeit briefly, in the Martian mornings. The patches of frost appear for a few hours around sunrise before they evaporate in the sunlight, showcasing a fascinating cycle of water activity on Mars.
“What we’re seeing may be a remnant of an ancient climate cycle on modern Mars, where you had precipitation and maybe even snowfall on these volcanoes in the past,” Valantinas said. “The amount of frost represents about 1,50,000 tonnes of water swapping between surface and atmosphere each day during the cold seasons, the equivalent of roughly 60 Olympic swimming pools.”
The presence of frost suggests that water vapor is moving through the Martian atmosphere and condensing in specific regions, challenging the notion that Mars is entirely devoid of active hydrological processes.
“This finding could be crucial for modeling water’s existence on Mars that could aid in future human exploration missions,” Valentinas explained. The study’s authors hope that further research and computer simulations of the frost formation and evaporation processes will shed light on Mars’ water dynamics and inform future exploration strategies.