New Study Explains Mars’ Earth-Like Gullies Without Liquid Water

Mysterious formations on Mars that resemble Earth’s water-carved gullies may actually be shaped by entirely different mechanisms. Recent investigations suggest that seasonal carbon dioxide frost, which behaves temporarily like a flowing fluid, is responsible for creating these features rather than liquid water.

Mars’ gullies have intrigued scientists for years due to their resemblance to channels and sediment deposits formed by water on Earth. This similarity sparked questions about whether liquid water still influences Martian surface changes today.

Images from orbiting spacecraft have even shown that some gullies undergo changes over time. However, Mars’ thin atmosphere and frigid temperatures challenge the idea that surface liquid water is stable or widespread.

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Apolline Leclef and her team from the Institut d’Astrophysique Spatiale at Université Paris-Saclay investigated a region of deep polar depressions near Mars’ south pole called Sisyphi Cavi. Their findings, published on the arXiv preprint archive, point to carbon dioxide frost as the agent driving these seasonal landscape transformations.

Water Not Responsible for Martian Gullies

To decipher the origin of these landforms, the researchers examined data from NASA’s Mars Reconnaissance Orbiter (MRO) and the European Space Agency’s Mars Express missions. They studied spectral data captured by the Compact Reconnaissance Imaging Spectrometer for Mars (CRISM) on MRO and the OMEGA spectrometer onboard Mars Express.

The team did not find spectral signs of liquid water in active gully regions, specifically searching for the characteristic water absorption at 1.5 micrometers during the spring season when carbon dioxide frost disappears. These markers were absent, ruling out liquid water as the gully-formation agent.

Minerals such as salts and clays were identified nearby but were located mostly on elevated terrain and crater edges, disconnected from the gullies themselves. This pushed researchers to consider seasonal carbon dioxide ice processes as the key factor influencing these dynamic features.

Martian Geysers Don’t Explain the Gullies

Initially, scientists hypothesized that Martian gullies might be linked to jets of carbon dioxide gas erupting beneath dry ice layers, akin to geysers. Unlike terrestrial geysers powered by heat and liquid water underground, these Martian geysers are driven by sunlight sublimating CO2 ice and releasing pressurized gas under transparent ice.

During winter, dry ice blankets parts of Mars. When spring arrives, sunlight warms the dark ground below, causing trapped CO2 to gasify. The pressure forces cracks and shoots out dark sand and soil, forming dark spots captured by orbiters.

However, the timing of these geysers peaks near the spring equinox, whereas gully activity tends to occur later in mid to late spring. This temporal mismatch led researchers to explore alternative mechanisms involving carbon dioxide frost.

A Novel Mechanism for Erosion

The most likely explanation proposed is carbon dioxide frost fluidization. Gas escaping through the frozen surface creates a slippery layer beneath ice and sediment, allowing them to glide downhill more easily.

This process is comparable to how an air hockey puck glides on a cushion of air. Similarly, dry ice mixed with soil could rapidly flow down slopes, cutting channels and depositing sediments that appear similar to water erosion structures on Earth.

The team concludes that this CO2-based seasonal mechanism sufficiently accounts for the observed erosion on Mars, negating the need to invoke liquid water. Together, the planet’s frost cycles, sunlight exposure, and thin atmosphere collaborate to mold these distinctive gullies.

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