Mars may have been born a blue and water-covered world long before Earth was even complete, according to new research. The discovery could give scientists a window into an overlooked chapter in Mars’ history.
In a recent study published in Earth and Planetary Science Letters, a team of researchers, including several from Arizona State University, found that Mars’ earliest atmosphere was much denser than it is today and composed mostly of molecular hydrogen, quite unlike the tenuous carbon dioxide atmosphere , which it preserves today.
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Despite being the lightest molecule, hydrogen would have had major implications for Mars’ earliest climate. As it turns out, molecular hydrogen is a powerful greenhouse gas.
“It is paradoxical that so many observations point to liquid water on early Mars, even though water is freezing on present-day Mars and the ancient Sun was 30% dimmer than it is today,” said Steve Desch, professor of astrophysics at the School of Earth and ASU Space Research and one of the team scientists. “Traditionally viewed greenhouse gases like CO2 would freeze on early Mars. (Hydrogen) in the atmosphere is an unexpected way to stabilize liquid water.”
According to the team’s calculations, molecular hydrogen is a greenhouse gas potent enough to keep very early oceans of warm to hot water stable on the surface of Mars for many millions of years, until the hydrogen was gradually lost to space.
A different kind of atmosphere
To determine the composition of the ancient atmosphere on Mars, the team’s scientists developed the first evolutionary models, which include high-temperature processes associated with the formation of Mars in a molten state and the formation of the first oceans and atmospheres. These models showed that the main gases escaping from the molten rock would be a mixture of molecular hydrogen and water vapor.
The results of the models showed that water vapor in the Martian atmosphere behaved like water vapor in Earth’s atmosphere today: it condensed as clouds in the lower atmosphere and created a ‘drier’ upper atmosphere. Molecular hydrogen, on the other hand, did not condense anywhere and was the main component of the upper Martian atmosphere. From there, this light molecule was lost into space.
“This important finding – that water vapor is condensed and retained on early Mars, while molecular hydrogen does not condense and cannot escape – allows the model to be directly linked to measurements from spacecraft, particularly the Mars Science Laboratory’s Curiosity rover,” said Kaveh Pahlevan, research fellow at the SETI Institute and lead author of the study.
Hydrogen from Mars, then and now
The new model has enabled new interpretations of deuterium-to-hydrogen (D/H) data from Mars samples analyzed in laboratories on Earth and by NASA rovers on Mars.
Hydrogen atoms in molecules can be either normal hydrogen (a nucleus with one proton) or “heavy” hydrogen called deuterium (a nucleus with one proton and one neutron). The number of deuterium atoms in a sample divided by the number of normal hydrogen atoms is called the deuterium-to-hydrogen or D/H ratio.
Meteorites from Mars are mostly magmatic rocks, essentially solidified lavas. They formed when the interior of Mars melted and magma rose to the surface. The water dissolved in these inner (derived from the mantle) samples contains hydrogen with a D/H ratio similar to that of Earth’s oceans, suggesting that the two planets started out and watered out with very similar D/H ratios same source came from the early solar system.
In contrast, when the Mars Science Laboratory measured the isotopes of hydrogen in an ancient 3-billion-year-old clay on the surface of Mars, they found a D/H ratio value about three times that of Earth’s oceans. Therefore, the hydrosphere of Mars — the reservoir of surface water that reacted with rocks to form these clays — must have had a high concentration of deuterium compared to hydrogen. The only plausible way to achieve this level of deuterium enrichment is to lose most of the hydrogen gas to space: regular hydrogen is lost, but deuterium, which is slightly heavier, is not lost as quickly.
The research from this comprehensive model shows that if the Martian atmosphere were dense and hydrogen-rich at the time of its formation, the surface water would be naturally enriched in deuterium by a factor of two to three compared to the interior, exactly what the Mars Science Laboratory observes Has.
“This is the first model to naturally reproduce these observations, giving us some confidence that the evolutionary scenario we have described corresponds to the earliest events on Mars,” Pahlevan said.
A boost for life on early Mars?
Hydrogen atmospheres can even be favorable for the emergence of life. The Stanley Miller experiments of the mid-20th century showed that prebiotic molecules involved in the origin of life form easily in such hydrogen-rich, “reducing” atmospheres, but not so easily in hydrogen-poor, “oxidizing” ones ” Atmospheres. Atmospheres like those of today’s Earth or Mars.
The team’s research suggests that early Mars was at least as promising a place for life to emerge as early Earth, if not more so, long before Earth existed. The earth as we know it only formed after the moon-forming impact, after tens of millions of years of evolution of the solar system. Long before that, Mars may have had a dense, hydrogen-rich atmosphere, mild temperatures, and a surface covered with blue oceans.
In addition to Desch and Pahlevan, the publication’s authors include Lindy Elkins-Tanton and Peter Buseck, both affiliated with ASU’s School of Earth and Space Exploration (Buseck is also affiliated with ASU’s School of Molecular Sciences), and Laura Schaefer, affiliated with the Department of Geological Sciences at Stanford University.
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