For decades, the Red Planet has fascinated scientists and dreamers alike. Its dusty red plains, colossal volcanoes, and canyon systems tell stories of a world that was once dynamic and possibly habitable. Yet despite countless robotic missions and analyses of Martian soil and rock, no direct evidence of life has yet been found. What scientists have uncovered, however, are tantalizing surface features that suggest an active and ever-changing landscape — features that might even hold clues about Mars’ ancient past.
One such mystery involves the strange gullies etched into the sides of Martian dunes. These small, narrow channels resemble miniature riverbeds and canyons, hinting at processes once thought to require liquid water. But in a planet where the surface pressure and temperature make water unstable, another explanation was needed. Enter Earth scientist Dr. Lonneke Roelofs from Utrecht University, whose groundbreaking research has revealed that frozen carbon dioxide (CO₂ ice) — not water — may be responsible for carving these enigmatic formations.
Her findings, published in Geophysical Research Letters, provide the first direct experimental evidence showing that CO₂ ice blocks can dig channels into Martian sand without any help from liquid water or wind. The implications of this discovery are profound — not only does it help solve a long-standing Martian mystery, but it also redefines how scientists think about the geological forces that shape cold, dry planets.
The Long-Standing Puzzle of Martian Gullies
Since the early 2000s, high-resolution images from spacecraft such as NASA’s Mars Reconnaissance Orbiter have shown dune slopes covered in thin, meandering channels. Some gullies appeared to form during the Martian winter or spring, puzzling scientists who expected water-related activity to occur only during warmer seasons. Early theories suggested that seasonal melting of subsurface ice might cause short-lived flows of salty water. Others proposed dry landslides or dust avalanches.
But many researchers noticed something unusual — the gullies were often found in regions where CO₂ frost accumulates during the frigid Martian winter. These clues hinted that carbon dioxide, not water, might be the main sculptor. Still, there was no direct proof of how this process could actually occur in nature.
Dr. Roelofs took up the challenge of testing this idea under controlled conditions. Through a combination of laboratory experiments and simulated Martian environments, she and her team set out to replicate the natural processes occurring on Mars — and what they discovered was astonishing.
Watching CO₂ Ice Create Gullies in the Lab
In her laboratory experiments, Roelofs demonstrated that blocks of frozen CO₂ can move and carve trenches in sand on their own — all through a fascinating physical process known as sublimation. Sublimation is when a solid turns directly into a gas without first becoming a liquid. On Mars, where atmospheric pressure is less than 1% of Earth’s, CO₂ ice behaves in dramatic ways.
During the Martian winter, temperatures can drop to nearly –120°C, causing carbon dioxide from the atmosphere to freeze and accumulate as a layer of frost or ice over dunes and crater slopes. When spring returns, sunlight warms the sand beneath the ice. The underside of each CO₂ block begins to sublimate rapidly, turning into gas.
Because gas expands much more than solid ice, pressure builds up beneath the block, causing it to “hover” slightly and even blast sand outward in all directions. “It felt like I was watching the sandworms in the film Dune,” Roelofs remarked, describing how the CO₂ blocks seemed to move like living creatures.
As the sublimation continues, the ice block slowly slides downhill, carving a deep, narrow trench bordered by ridges of displaced sand. Once all the CO₂ has vaporized, what remains is a long gully, nearly identical to those observed on Mars.
This discovery marks the first time scientists have directly observed the mechanism responsible for these unique landforms — a process that does not occur naturally anywhere on Earth.
Simulating Mars on Earth
To ensure her findings accurately represented real Martian conditions, Roelofs collaborated with master’s student Simone Visschers and traveled to the Open University in Milton Keynes, England. There, they used a specialized Mars chamber, a facility capable of mimicking the planet’s extremely thin atmosphere, low pressure, and cold temperatures.
With financial support from the British Society of Geomorphology, the researchers conducted a series of experiments. They simulated dune slopes at different angles and released blocks of CO₂ ice from the top. After numerous trials, they found the perfect combination of slope and temperature conditions that caused the ice to begin moving and digging — just as seen in satellite images from Mars.
“The CO₂ ice block began to dig into the slope and move downwards just like a burrowing mole or the sandworms from Dune. It looked very strange!” said Roelofs. Their data confirmed that sublimation-driven movement could indeed reproduce Martian gully patterns — a remarkable demonstration of extraterrestrial geology in action.
From Ice Blocks to Gully Networks
So how do these CO₂ ice blocks form in the first place? According to Roelofs, during winter in Mars’ southern hemisphere, thick layers of CO₂ ice accumulate on the dunes — sometimes reaching up to 70 centimeters thick. When spring arrives, most of the ice sublimates, but patches on the shaded sides of dunes remain longer.
As the temperature rises, these remaining patches break off into large chunks, which then tumble downhill under the influence of gravity and sublimation pressure. As they move, they sculpt deep gullies into the sand. When they finally come to rest at the base of the slope, the remaining ice completely vaporizes, leaving behind only hollow depressions and ridged channels.
Through these repeating seasonal cycles, entire dune fields become covered with intricate gully systems — evidence of active landscape formation happening today on Mars.
Why This Discovery Matters
Dr. Roelofs’ research provides a crucial piece of the Martian puzzle. It shows that complex geological features can form in the complete absence of water, expanding scientists’ understanding of how other cold and dry worlds in our solar system — such as Pluto or Triton — might also evolve.
Moreover, her work challenges the long-standing assumption that gully-like features on Mars must have been created by flowing liquid water, a key requirement for life as we know it. While her findings make it less likely that these particular gullies are evidence of past biology, they highlight how active and dynamic the planet still is today.
For Roelofs, the fascination with Mars goes beyond geology. “Mars is our nearest neighbour. It is the only rocky planet close to the ‘green zone’ of our solar system,” she explains. This “green zone,” or habitable zone, is the region around the Sun where temperatures could allow for liquid water — and possibly life.
Studying how Mars’ surface evolves helps scientists not only understand that planet’s history but also gain new insights into Earth’s own geological processes. “By studying other planets, we step outside our usual frameworks,” says Roelofs. “It allows us to ask slightly different questions — and sometimes, that leads to new insights about our own world.”
A Window Into Mars’ Past and Future
The Red Planet remains a world of riddles. It may never have had seas or forests like Earth, but its ever-changing surface tells a story of frost, dust, and frozen air dancing in the thin sunlight. The gullies that once seemed to whisper of ancient rivers now speak of a different kind of beauty — one sculpted by physics rather than biology. Dr. Roelofs’ CO₂ ice experiments remind us that life isn’t the only thing that shapes worlds. Even on a planet where the air is too thin to breathe and the cold too bitter to endure, natural processes continue to sculpt landscapes in astonishing ways. Whether or not Mars ever hosted life, it remains a planet very much alive — geologically speaking. As missions like ExoMars and Mars Sample Return continue to explore the planet’s surface, discoveries like Roelofs’ bring us one step closer to understanding Mars not as a dead world, but as a dynamic and evolving one — a place where even ice can move mountains.
Story Source: Utrecht University.
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