Explosive Dry Ice, Not Water, Carves Mysterious Gullies on Mars’s Dunes

Settling a Decade-Long Martian Mystery: The Role of Solid Carbon Dioxide

For years, the strange, winding channels etched into the dunes of Mars have fueled intense scientific debate. These features, known as sinuous gullies, were once considered prime evidence for recent, flowing liquid water on the Red Planet—a tantalizing prospect for the search for extraterrestrial life. However, a definitive new experiment, replicating the harsh Martian environment, has finally settled the mystery: the gullies are carved not by liquid water, but by the explosive sublimation of dry ice.

This finding, published in the journal Scientific Reports, confirms that the geological processes shaping the Martian surface today are dominated by carbon dioxide ice, fundamentally changing how scientists interpret the planet’s dynamic landscapes.

The Mechanism: Pressure Cooker Beneath the Sand

The key to understanding these Martian features lies in the behavior of dry ice, or solid carbon dioxide (CO2), under the planet’s low atmospheric pressure and extreme cold. Unlike on Earth, where water ice melts into liquid, CO2 ice on Mars transitions directly from a solid to a gas—a process called sublimation.

During the Martian winter, vast quantities of dry ice accumulate and become trapped beneath layers of sand and dust on the dunes. As spring arrives, the sun warms the surface layers, heating the dry ice below. Because the CO2 is trapped, the pressure of the rapidly expanding gas builds up dramatically.

Simulating the Martian Spring

To test this hypothesis, researchers conducted a groundbreaking experiment in a vacuum chamber designed to mimic the conditions on Mars. This high-fidelity simulation was performed at the Open University Mars Simulation Chamber in the UK.

The Experimental Setup:

• Researchers placed blocks of dry ice beneath layers of fine sand, replicating the dune structure.
• The chamber was pumped down to the extremely low pressure characteristic of the Martian atmosphere.
• The temperature was carefully controlled to simulate the warming of the Martian spring.

When the dry ice blocks began to sublimate, the gas pressure became too great for the overlying sand to contain. The result was a dramatic, explosive venting of CO2 gas, which carved intricate channels as it escaped.

“The channels we created in the lab, formed by the explosive venting of pressurized CO2 gas, were a near-perfect match for the sinuous gullies observed on Mars,” stated the research team. “This provides compelling evidence that dry ice, not liquid water, is the primary agent responsible for these specific features.”

Implications for Martian Geology and the Search for Life

This discovery has significant implications for planetary science, particularly in interpreting images captured by orbiters like the Mars Reconnaissance Orbiter (MRO) and its high-resolution camera, HiRISE.

For years, the appearance of these gullies—which resemble terrestrial water erosion features—led many scientists to believe they were evidence of recent liquid water activity, possibly even seasonal flows. The new evidence firmly shifts the focus away from liquid water as the cause of these specific dune features.

Distinguishing Martian Processes

While this experiment rules out liquid water as the cause of the sinuous dune gullies, it does not negate the existence of water ice or other forms of water on Mars. Instead, it highlights the unique and powerful geological forces driven by carbon dioxide, which dominates many seasonal processes on the planet.

Key Differences in Erosion:

Understanding which features are caused by CO2 and which might be linked to water is crucial for selecting future landing sites and prioritizing areas for astrobiological investigation.

Key Takeaways

This groundbreaking simulation confirms the power of seasonal CO2 cycles in shaping the Martian surface. Here are the essential points for understanding this discovery:

• Primary Cause: The mysterious sinuous gullies in Martian dunes are created by the explosive sublimation of dry ice (solid CO2).
• Mechanism: Dry ice trapped beneath the sand turns rapidly into gas during spring, building up pressure until it vents violently, carving the channels.
• Evidence: Laboratory experiments replicating the Martian atmosphere produced channels that perfectly match images taken by the MRO HiRISE camera.
• Impact: This finding strongly suggests that these specific dune features are not evidence of recent liquid water activity, focusing the search for water-driven erosion on other geological formations.
• Expertise: The research demonstrates the critical role of high-fidelity simulation chambers in solving planetary mysteries that cannot be fully understood through orbital observation alone.

Conclusion

The resolution of the Martian gully mystery underscores the need for Earth-based simulations to fully grasp the exotic physics governing other worlds. By definitively linking the sinuous dune gullies to the powerful, seasonal cycles of carbon dioxide, scientists can now refine their models of Martian climate and geological activity. This clarity allows the scientific community to focus the search for liquid water—and potential signs of life—on features where CO2 processes have been definitively ruled out, making the overall exploration effort more targeted and efficient.