Mars is known for its dry riverbeds and lake basins, which suggest that liquid once flowed on its surface.
For years, scientists have believed that this liquid was water.
However, a new article in Nature Geoscience presents an intriguing alternative: the liquid could have been carbon dioxide (CO₂).
According to Michael Hecht, lead author of the study and a research scientist at MIT, liquid CO₂ might have been easier to form than water under the conditions of ancient Mars.
“We’re not saying it’s the only explanation, but it’s a possibility worth exploring,” says Hecht.
Why CO₂ could be the key
On Mars today, CO₂ exists as a gas in the atmosphere and as solid ice in polar caps.
However, under specific conditions in the distant past, it might have condensed into a liquid.
While scientists have considered liquid CO₂ as a possible explanation for Mars’ river channels before, most believed the mineral evidence pointed firmly to water.
The new study changes that perspective.
It highlights findings from Earth-based carbon sequestration research, where CO₂ is stored underground as a liquid to combat climate change. These studies reveal that minerals can undergo chemical changes in liquid CO₂—sometimes even faster than in water.
Hecht and his team argue that these CO₂-driven chemical reactions could explain the same types of minerals found on Mars today, including carbonates, phyllosilicates, and sulfates.
How liquid CO₂ could have existed
The paper suggests three ways liquid CO₂ might have been present on early Mars:
- Stable Surface Liquid: CO₂ could have pooled as a liquid under specific temperature and pressure conditions.
- Basal Melting: CO₂ ice might have melted into liquid at its base.
- Subsurface Reservoirs: Liquid CO₂ could have been trapped underground, shaping the surface through eruptions or seepage.
The researchers emphasize that conditions on ancient Mars—cold and with low atmospheric pressure—would have been very different from the laboratory tests on Earth. More experiments are needed to confirm whether similar chemical reactions could happen under Martian conditions.
If liquid CO₂ played a role in shaping Mars, it could change how we understand the planet’s history and the role of water in its development. It might also shift the search for evidence of life, as scientists consider whether life could have thrived in environments dominated by CO₂.
“We can’t say for sure if this theory is true,” says Hecht. “But the possibility is strong enough that we shouldn’t ignore it.”
The study offers a fresh piece of the puzzle in understanding Mars’ mysterious past—one that could lead to surprising discoveries about the Red Planet.
