Mars could be born blue before the Earth finished forming

Oct. 21 () –

According to new research, Mars may was born as a world blue and covered with water, long before the Earth finished forming.

In a recent study published in Earth and Planetary Science Lettersa team of researchers discovered that the oldest atmosphere on Mars was much denser than today’s and was composed primarily of molecular hydrogen, very different from the thin carbon dioxide atmosphere it retains today.

Although it is the lightest molecule, hydrogen would have had big implications for the early climate of Mars. It turns out that molecular hydrogen is a powerful greenhouse gas.

“It’s a paradox that so many observations suggest liquid water on early Mars, even though water freezes on Mars today, and the ancient sun was 30% darker than today,” he said. it’s a statement Steve Desch, a professor of astrophysics at Arizona State University and one of the team’s scientists. “Greenhouse gases traditionally thought of as 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 strong enough to have allowed the first warm-to-hot water oceans to remain stable on the Martian surface for many millions of years. until the hydrogen was gradually lost to space.

To determine the composition of Mars’ ancient atmosphere, team scientists developed the first evolutionary models that include high-temperature processes associated with the formation of Mars in a molten state and the formation of the first oceans and atmosphere. These models showed that the main gases emerging from the molten rock would be a mixture of molecular hydrogen and water vapour.

The results of the models revealed that water vapor in the Martian atmosphere behaved like water vapor in Earth’s atmosphere today: it condensed in the lower atmosphere as clouds, creating a “drier” upper atmosphere. Molecular hydrogen, by contrast, did not condense anywhere and was the main component of the upper atmosphere of Mars. From there, this light molecule was lost in space.

“This key idea, that water vapor condenses and is retained on early Mars, while molecular hydrogen does not condense and can escape, allows the model to link directly to measurements made by a space mission, specifically the rover Curiosity,” said Kaveh Pahlevan, a research scientist at the SETI Institute and lead author of the study.

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 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 ratio or D/H.

Meteorites from Mars are mostly igneous rocks, basically solidified magmas. They formed when the interior of Mars melted and magma rose to the surface. The dissolved water in these interior samples (derived from the mantle) contains hydrogen with a D/H ratio similar to that of Earth’s oceans, indicating that the two planets started out with very similar D/H ratios. and that its water came from the same source in the early solar system.

In contrast, when Curiosity measured hydrogen isotopes in a 3-billion-year-old clay on the Martian surface, it 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 relative to hydrogen. The only plausible way to have this level of deuterium enrichment is to lose most of the hydrogen gas to space.: Normal hydrogen is lost, but deuterium, being slightly heavier, is not lost as quickly.

Investigation of this comprehensive model shows that if the Martian atmosphere were dense and hydrogen-rich at the time of its formation, then surface waters would naturally be enriched in deuterium by a factor of two to three, relative to the interior, which is precisely what Curiosity observed.

“This is the first model that naturally reproduces these observations.which gives us some confidence that the evolutionary scenario we have described corresponds to the earliest events on Mars,” Pahlevan said.