Science and Tech

Not all the liquid on Mars was necessarily water

Under the lower pressure conditions characteristic of early Mars, water would float in the LCO2.

Under the lower pressure conditions characteristic of early Mars, water would float in the LCO2. – TODD SCHAEF/EARL MATTSON

Dec. 5 () –

Water is only one of two liquids possible under the conditions believed to have existed on ancient Mars, a new study published in the journal warns. Nature Geoscience.

The other is liquid carbon dioxide (CO2), and it may actually be easier for CO2 in the atmosphere to condense into liquid under these conditions than for water ice to melt.

Although others have suggested that liquid CO2 (LCO2) could be the source of some of the river channels observed on Mars, the mineral evidence seems to point exclusively to water. However, the new article cites recent studies on carbon sequestration, the process of burying liquefied CO2 recovered from the Earth’s atmosphere deep in underground cavernswhich show that similar mineral alteration can occur in liquid CO2 and water, sometimes even more rapidly.

The new article, published in Nature Goescienceis led by Michael Hecht, principal investigator of the MOXIE instrument aboard NASA’s Perseverance rover on Mars. Hecht, a research scientist at MIT’s Haystack Observatory and former associate director, says in a statement: “Understanding how enough liquid water could have flowed on early Mars to explain the morphology and mineralogy we see today is probably the biggest unresolved question in Mars science. There is likely no single correct answer, and we are simply suggesting another possible piece of the puzzle.”

In the paper, the authors discuss the compatibility of their proposal with current knowledge of Martian atmospheric content and the implications for Martian surface mineralogy. They also explore the latest research on carbon sequestration and conclude that ““LCO2-mineral reactions are consistent with the predominant alteration products of Mars: carbonates, phyllosilicates and sulfates.”

The argument for the likely existence of liquid CO2 on the Martian surface is not an all-or-nothing scenario; Liquid CO2, liquid water, or a combination of these may have given rise to geomorphological and mineralogical evidence for the existence of a liquid Mars.

Three plausible cases of liquid CO2 on the Martian surface are proposed and analyzed: stable liquid on the surface, basal melt under CO2 ice, and underground deposits. The probability of each of them depends on the actual CO2 inventory at that time, as well as surface temperature conditions.

The authors recognize that the sequestration conditions tested, in which liquid CO2 is above room temperature at pressures of tens of atmospheres, are very different from the cold and relatively low pressure conditions that could have produced liquid CO2 in early Mars. They call for more laboratory research to be carried out under more realistic conditions to see if the same chemical reactions occur.

Hecht explains: “It’s hard to say how likely it is that this speculation about early Mars is actually true. What we can say, and are saying, is that the probability is high enough that it shouldn’t be ignored.”

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