Mars liquid may not be all water new findings reveal

The dry riverbeds and desolate lake beds of Mars hint at a time when liquid flowed across its surface, with many scientists believing this liquid was simply water. However, a recent Perspectives article in Nature Geoscience challenges this assumption.

The authors argue that under the ancient Martian conditions, liquid carbon dioxide (CO₂) may have been just as viable a candidate as water. Given the atmosphere’s properties at the time, CO₂ might have more readily transitioned into a liquid state compared to melting ice.

Although the idea of liquid CO₂ (LCO₂) contributing to Martian landscape formation has been proposed before, mineral evidence has often pointed exclusively towards the presence of water. However, this new research highlights findings from carbon sequestration studies, which show that LCO₂ can lead to similar, if not quicker, mineral alterations as water.

Leading the study is Michael Hecht, the principal investigator of the MOXIE instrument on NASA’s Mars Rover Perseverance. Hecht, a research scientist at MIT’s Haystack Observatory, states, “One of the biggest unresolved questions in Mars science is understanding how liquid water could have flowed in sufficient quantities to shape the planet’s current morphology and mineralogy.” He emphasizes that there may not be a singular answer and that their proposal could be an integral piece of the overall picture.

In their paper, the team evaluates how their hypothesis aligns with what is known about Martian atmospheric composition and its effects on surface mineralogy. They closely examine recent research related to carbon sequestration, concluding that “LCO₂–mineral reactions are consistent with the primary alteration products observed on Mars: carbonates, phyllosilicates, and sulfates.”

The authors stress that the possibility of LCO₂ existing on Mars doesn’t exclude the potential presence of liquid water; rather, it suggests a more complex scenario where either liquid form—water, CO₂, or a combination of both—could account for the geological and mineralogical features we observe today.

They propose three credible scenarios for the existence of liquid CO₂ on the Martian surface: stable liquid, melting beneath CO₂ ice, and subsurface reservoirs. The feasibility of each scenario is contingent upon the levels of atmospheric CO₂ and the temperature conditions prevalent at the time.

It’s essential to note that the conditions studied in sequestration experiments—where liquid CO₂ is maintained above room temperature at high pressures—differ significantly from the frigid, low-pressure environment of early Mars. Thus, the authors advocate for further laboratory work under conditions that more accurately reflect Mars’ ancient climate to verify if the same reactions can occur.

Hecht concludes, “It’s challenging to ascertain how plausible our hypothesis about early Mars is. Nonetheless, the potential for such conditions is significant enough that it merits serious consideration.”