Introduction

Recent explorations of Mars have unveiled dry river channels and ancient lake beds, suggesting that liquid once flowed on the planet's surface, leading many scientists to firmly conclude that this liquid was nothing other than water. However, a thought-provoking new paper from researchers published in *Nature Geoscience* proposes an alternative theory: that some minerals on Mars may have formed from liquid carbon dioxide (CO₂) instead.

Research Insights

The study, led by Michael Hecht, the principal investigator of the MOXIE (Mars Oxygen In-Situ Resource Utilization Experiment) instrument aboard NASA's Perseverance rover, suggests that liquid CO₂ could have been more prevalent under the conditions of ancient Mars than previously thought. Hecht, a research scientist at MIT's Haystack Observatory, emphasizes that unraveling the mystery of liquid presence on early Mars is one of the most critical unresolved questions in Martian science. He states, “There is likely no one right answer, and we are merely suggesting another possible piece of the puzzle.”

Comparison with Water Theories

While prior theories concentrated on water as the main liquid, Hecht and his colleagues highlight a growing body of research indicating that liquid CO₂ can result in mineral changes similar to those caused by water—and sometimes even more swiftly. This is significant in light of recent studies on carbon sequestration on Earth, where liquefied CO₂ stored deep underground undergoes mineral alteration.

Supporting Scenarios

The authors discuss three scenarios that could support the existence of liquid CO₂ on the Martian surface: stable surface liquid, basal melting beneath CO₂ ice, and subsurface reservoirs. The feasibility of each scenario rests on the concentration of CO₂ at that time, as well as the surface temperature conditions.

Mineral Evidence and Future Research

One compelling argument for liquid CO₂ is that the presence of carbonates, phyllosilicates, and sulfates—minerals altered through liquid interactions—could also align with CO₂ reactions. The research team stresses that the interactions between liquid CO₂ and Martian minerals warrant further experimental validation under more authentic conditions that mimic early Mars’ atmosphere, which was significantly colder and of lower pressure.

Conclusion and Implications

Hecht cautions, “It's difficult to say how likely it is that this speculation about early Mars is actually true. However, we argue that the possibility is compelling enough that it cannot be casually dismissed.” As Mars continues to capture the attention of scientists and space enthusiasts alike, these findings could revolutionize our understanding of the planet's geological history. If liquid CO₂ did play a significant role in shaping Mars as we know it today, what other secrets does the red planet hold? The exploration for answers is just beginning!