Planetary scientists have spotted patches of water frost atop the Tharsis volcanoes on Mars, the tallest volcanic mountains in the solar system, according to a new study published in Nature Geoscience. The discovery, made by an international team of researchers, marks the first time frost has been detected near the planet’s equator, challenging existing understanding of Mars’ climate dynamics.
Adomas Valantinas, a postdoctoral fellow at Brown University who led the work as a Ph.D. student at the University of Bern, explained, “We thought it was improbable for frost to form around Mars’ equator, as the mix of sunshine and thin atmosphere keeps temperatures during the day relatively high at both the surface and mountaintop — unlike what we see on Earth, where you might expect to see frosty peaks. 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.”
Thin but Vast Frost Deposits
The frost, present for only a few hours after sunrise before evaporating, is incredibly thin—likely only one-hundredth of a millimeter thick or about the width of a human hair. Despite its thinness, the frost is quite vast, constituting at least 150,000 tons of water that swaps between the surface and atmosphere each day during the cold seasons, equivalent to roughly 60 Olympic-size swimming pools.
The Tharsis region, where the frost was found, hosts numerous volcanoes that tower above the surrounding plains at heights ranging from one to two times that of Earth’s Mount Everest. The frost sits in the calderas of the volcanoes, large hollows at their summits created during past eruptions. The researchers propose that the way the air circulates above these mountains creates a unique microclimate that allows the thin patches of frost to form.
Unlocking Mars’ Remaining Secrets
The researchers believe that modeling how the frosts form could allow scientists to reveal more of Mars’ remaining secrets, including understanding where water exists and how it moves, as well as understanding the planet’s complex atmospheric dynamics, which is essential for future exploration and the search for possible signs of life.
The frost was detected using high-resolution color images from the Colour and Stereo Surface Imaging System (CaSSIS) onboard the European Space Agency’s Trace Gas Orbiter. The findings were then validated using independent observations from the High Resolution Stereo Camera onboard the ESA’s Mars Express orbiter and by the Nadir and Occultation for Mars Discovery spectrometer onboard the Trace Gas Orbiter.
Valantinas, who started analyzing the images in 2018, filtered the images based on where and when they were acquired, like the time of day and the season. This meticulous approach helped isolate spectral signatures indicative of water frost and where it formed on the Martian surface.
As Valantinas transitions to his role at Brown, he plans to continue his exploration of Martian mysteries while pivoting to astrobiology. Working in the lab of Brown planetary scientist Jack Mustard, he’ll work toward characterizing ancient hydrothermal environments that could have supported microbial life. Samples from these environments may one day be brought back to Earth by the NASA-lead Mars Sample Return mission.
“This notion of a second genesis, of life beyond Earth, has always fascinated me,” Valantinas said.