Geomorphological and mineralogical evidence is consistent with aqueous activity on ancient Mars, yet explaining the presence of substantial liquid water on early Mars remains challenging. Another fluid, liquid CO₂, was probably present during Martian history, at least in the subsurface, and could even have been stable at the surface under a sufficiently dense CO₂-rich early atmosphere. Liquid CO₂ flows have been proposed as an alternative to water to explain morphological features, but it is widely accepted that water is the fluid responsible for mineral alteration. Interestingly, however, experimental research on geologic sequestration on Earth has revealed a surprising degree of chemical reactivity between CO₂ fluid and minerals if the fluid is water-saturated, as it would probably have been on Mars. The resulting alteration products — carbonates, phyllosilicates and possibly sulfates — are consistent with minerals found on Mars today. We therefore propose that the formation of some of the aqueous mineral alteration observed on the Martian surface may have been mediated by liquid CO₂. Further laboratory investigations are needed to test this hypothesis.

地貌学和矿物学证据与古代火星上的水活动一致，但解释早期火星上存在大量液态水仍然具有挑战性。另一种流体，液态 CO₂，可能在火星历史上就存在，至少在地下，甚至可能在足够密集的富含 CO₂ 的早期大气中稳定在地表。液态 CO₂ 流已被提议作为水的替代品来解释形态特征，但人们普遍认为水是导致矿物蚀变的流体。然而，有趣的是，对地球上地质封存的实验研究表明，如果 CO 2 流体是水饱和的，那么 CO₂ 流体和矿物之间的化学反应程度会达到惊人的程度，就像在火星上一样。由此产生的蚀变产物——碳酸盐、层状硅酸盐和可能的硫酸盐——与今天在火星上发现的矿物一致。因此，我们提出，在火星表面观察到的一些含水矿物蚀变的形成可能是由液态 CO₂ 介导的。需要进一步的实验室调查来检验这一假设。