Representational Image

(ESA/Hubble, M. Kornmesser)

Scientists have long known that there’s more to Mars’ rugged red terrain than meets the eye, and that lakes and rivers once populated the otherwise dry planet. Some evidence even indicates that the Red Planet still has frozen water at its northern pole. But a newly constructed model on the evolution of the Martian atmosphere indicates that Mars was born wet — suggesting that it could have perhaps supported life!

Exploring an overlooked chapter in Mars’ early history, this new study has revealed that at its inception, Mars possessed a dense atmosphere that allowed warm-to-hot waters to exist for millions of years.

Modelling Mars’ early atmosphere

The model connects the development of the Martian atmosphere from Mars’ molten origin to the formation of the first oceans and atmosphere. According to it, the water vapour in the Martian atmosphere was concentrated in the lower atmosphere, similar to how it is currently on Earth, while the upper atmosphere of Mars was “dry” because it condensed out as clouds at lower altitudes in the atmosphere. Molecular hydrogen (H2), on the other hand, did not condense and was taken to Mars’ upper atmosphere, where it was then lost to space.

This finding that water vapour condensed and was kept on early Mars, whereas molecular hydrogen did not condense and escaped, allows the model to be directly linked to the measurements made by the Curiosity rover. The Mars Science Laboratory (MSL) Rover Environmental Monitoring Station humidity instrument (REMS-H) onboard the Curiosity rover measures daily minimum water vapour mixing ratios.

“This finding is significant because H2 is known to be a strong greenhouse gas in dense environments. This dense atmosphere would have produced a strong greenhouse effect, allowing very early warm-to-hot water oceans to be stable on the Martian surface for millions of years until the H2 was gradually lost to space. For this reason, we infer that—at a time before the Earth itself had formed—Mars was born wet,” said Kaveh Pahlevan, SETI Institute research scientist.

Evidence for life on Mars

Meanwhile, the model looks into the deuterium (heavy hydrogen) and hydrogen ratio (D/H) of various Martian samples, such as meteorites and Curiosity samples. Mars meteorites are mostly igneous rocks that formed when magma erupted from deep inside the Martian crust to the planet’s outer layers. And this D/H ratio in these inner (mantle-derived) igneous rocks is comparable to that of Earth’s oceans, implying that the two planets had identical D/H ratios in the early Solar System and that their water originated from the same source!

But what limits this model is that the D/H ratio of 3-billion-year-old clay analysed by the Curiosity on the surface of Mars is about three times higher than that of the oceans on Earth. This indicates that Mars’ surface water reservoir had significantly concentrated deuterium in relation to hydrogen by the time these ancient clays formed.

The only process known to produce this level of deuterium concentration is the preferential loss of the lighter H isotope to space. What this means is that the original Martian atmosphere must have been exceedingly dense (more than 1000x as dense as the contemporary atmosphere), largely consisting of molecular hydrogen (H2).

According to tests dating back to the mid-twentieth century, prebiotic chemicals associated with the beginning of life can arise swiftly in such H2-rich atmospheres, although not as readily in H2-poor (or more “oxidising”) atmospheres. In conclusion, Mars was very likely a site for the formation of life and was at least as hospitable as, if not more promising, than early Earth.

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