Dry river channels and lake beds on Mars have long captured the imagination of scientists and enthusiasts alike, suggesting a bygone era when liquid flowed abundantly across the Martian surface. Conventional wisdom has pointed to water as the primary agent responsible for these geological features. However, recent insights challenge this notion, introducing the possibility that the liquid in question may not have been exclusively water, but rather liquid carbon dioxide (LCO2).
The suggestion that liquid CO2 could have played a role in shaping Mars’s surface is not merely speculative. Emerging research illustrates that, under the atmospheric conditions believed to have existed on ancient Mars, LCO2 may have been more readily available than melted water ice. This perspective opens the door to a reinterpretation of the mineral evidence gathered by orbiters and landers, which has traditionally been interpreted as a definitive indication of water.
Recent studies related to carbon sequestration, a process of capturing and storing atmospheric CO2, reveal that similar mineral transformations can occur in LCO2 as in water. In fact, these reactions can transpire at a faster rate in liquid CO2, indicating that some of the minerals observed on Mars could have formed through processes involving CO2, rather than H2O.
Michael Hecht, a prominent researcher from MIT’s Haystack Observatory and principal investigator for the MOXIE instrument on the Mars Perseverance rover, encapsulates the gravity of the situation succinctly: “Understanding how sufficient liquid water was able to flow on early Mars to explain the morphology and mineralogy we see today is probably the greatest unsettled question of Mars science.” His insights suggest that the geological story of Mars is likely more complex than a simple narrative dominated by water.
Three potential scenarios for the existence of liquid CO2 on Mars are outlined in current research:
- Stable surface liquid: This scenario posits that liquid CO2 could have existed freely on the Martian surface under certain temperature and pressure conditions.
- Basal melting under CO2 ice: This concept suggests that CO2 ice could have melted from beneath, yielding liquid CO2 that helped shape the landscape.
- Subsurface reservoirs: It’s also possible that liquid CO2 formed in underground reservoirs, impacting the mineralization processes observed today.
The plausibility of each of these scenarios hinges on various factors, including the atmospheric CO2 inventory and the thermal state of ancient Mars. Importantly, the conditions studied in carbon sequestration experiments differ significantly from the harsh, cold environment of early Mars, raising questions about the generalizability of those findings. Hecht and his colleagues advocate for more laboratory testing under conditions mimicking the Martian environment to better understand the reactions of LCO2 with Martian minerals.
The implications of these findings extend beyond mere academic curiosity. If liquid CO2 played a significant role in the history of Mars, it could reshape our understanding of the planet’s climate evolution, habitability, and the potential for past life. As Hecht aptly puts it, “What we can say, and we are saying, is that the likelihood is high enough that the possibility should not be ignored.”
This emerging narrative invites a deeper exploration of Mars’s geological past and presents a fascinating opportunity to reconsider how we interpret the landscape we observe today. As research continues, the question of whether ancient Mars was a world dominated by water or a diverse landscape shaped by multiple liquids remains one of the great mysteries of planetary science.
