Scientists have long known that there is more to the rugged red terrain of Mars than meets the eye, and that lakes and rivers once inhabited the parched planet. Some evidence even suggests that the Red Planet still has frozen water at its North Pole. But the newly built model of the evolution of Mars’ atmosphere suggests that Mars was born wet – suggesting that it may have supported life!
Exploring an overlooked chapter in Mars’ early history, this new study reveals that from its inception Mars had a dense atmosphere that allowed warm to hot water for millions of years.
Modeling the early atmosphere of Mars
The model links the evolution of the Martian atmosphere from a molten Martian origin to the formation of the first oceans and atmospheres. According to her, the water vapor in the Martian atmosphere is concentrated in the lower atmosphere, similar to what is currently on Earth, while the upper atmosphere of Mars was “dry” because it condenses in the form of clouds at lower altitudes in the atmosphere. On the other hand, molecular hydrogen (H2) did not condense and was carried into the upper atmosphere of Mars, where it was subsequently lost to space.
This finding that water vapor condensed and held on early Mars, while the molecular hydrogen neither condensed nor escaped, allows the model to relate directly to measurements made by the Curiosity probe. The Mars Science Laboratory (MSL) Rover The Curiosity Environmental Monitoring Station (REMS-H) moisture monitor measures daily minimum mixing rates of water vapor.
“This finding is important because H2 is known to be a potent greenhouse gas in dense environments. This dense atmosphere would have produced a strong greenhouse effect, allowing warm to very hot water oceans to settle on Mars for millions of years until H2 is lost. For this reason, we conclude that — at some time before Earth itself formed — Mars was born wet, said Kaveh Pahlifan, a research scientist at the SETI Institute.
Evidence of life on Mars
Meanwhile, the model looks at the deuterium (heavy hydrogen) and hydrogen (D/H) ratio of various Martian samples, such as meteorites and Curiosity samples. Mars meteorites are mostly igneous rocks that formed when magma erupted from the depths of Mars’ crust into the planet’s outer layers. And this D/H ratio in these inner igneous rocks (derived from the mantle) is comparable to that found in Earth’s oceans, which means that the two planets had identical D/H ratios in the early solar system and that their water originated from the same source!
What limits this model, however, is that the D/H ratio of a 3-billion-year-old clay analyzed by Curiosity on Mars is three times higher than that of the oceans on Earth. This indicates that Mars’ surface water reservoir had too concentrated deuterium relative 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 atmosphere of Mars must have been extremely dense (more than 1,000 times the density of the contemporary atmosphere), and composed largely of molecular hydrogen (H2).
According to tests dating back to the mid-20th century, prebiotic chemicals associated with early life can emerge quickly in such H2-rich atmospheres, although not so readily in H2-poor (or more “oxidizing”) atmospheres. In conclusion, Mars was likely a life-forming site and was at least as hospitable, if not more promising, than early Earth.
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