New clues to Mars' early atmosphere suggest a wet planet capable of supporting life

New clues to Mars’ early atmosphere suggest a wet planet capable of supporting life

A 3D rendering of a wet blue planet. Credit: Planet Volumes/Anode on Unsplash

New research published in Earth and Planetary Science Letters suggests that Mars was born humid, with a dense atmosphere allowing warm to warm oceans for millions of years. To reach this conclusion, the researchers developed the first model of the evolution of the Martian atmosphere which links the high temperatures associated with the formation of Mars in the molten state to the formation of the first oceans and the atmosphere. .

This model shows that, as on modern Earth, water vapor in the Martian atmosphere was concentrated in the lower atmosphere and that Mars’ upper atmosphere was “dry” because the water vapor condensed as clouds at lower levels of the atmosphere. Molecular hydrogen (H2), on the other hand, did not condense and was transported to the upper atmosphere of Mars, where it was lost to space. This conclusion – that water vapor condensed and was retained in early Mars while molecular hydrogen did not condense and escaped – allows the model to be directly related to measurements made by spacecraft, in particular the Mars Science Laboratory’s Curiosity rover.

“We believe we modeled an overlooked chapter in Mars’ earliest history just after the planet was formed. To explain the data, the primordial Martian atmosphere must have been very dense (more than ~1000 times denser than the planet). modern atmosphere) and composed mainly of molecular hydrogen (H2),” said Kaveh Pahlevan, a researcher at the SETI Institute.

“This finding is significant because H2 is known to be a potent greenhouse gas in dense environments. This dense atmosphere would have produced a strong greenhouse effect, allowing the very first warm to warm water oceans to be stable on the surface of Mars for millions of years until the H2 slowly got lost in space. For this reason, we infer that, at a time before the formation of the Earth itself, Mars was born wet.”

The data binding the model are the deuterium to hydrogen (D/H) ratio (deuterium is the heavy isotope of hydrogen) of different Martian samples, including Martian meteorites and those analyzed by Curiosity. Mars meteorites are mostly igneous rocks – they formed when the interior of Mars melted and magma rose to the surface. The dissolved water in these inner igneous samples (derived from the mantle) has a deuterium to hydrogen ratio similar to that of Earth’s oceans, indicating that the two planets started out with similar D/H ratios and that their water came from from the same source. in the early solar system.

In contrast, Curiosity measured the D/H ratio of 3 billion-year-old ancient clay on the Martian surface and found that this value is about 3 times that of Earth’s oceans. Apparently, at the time these ancient clays formed, the reservoir of surface water on Mars – the hydrosphere – had a substantial concentration of deuterium relative to hydrogen. The only process known to produce this level of deuterium concentration (or “enrichment”) is the preferential loss of the lighter H isotope to space.

The model further shows that if the Martian atmosphere were H2-rich at the time of its formation (and more than ~1000x as dense as today), then the surface waters would be naturally enriched in deuterium by a factor of 2 to 3x compared to the interior, reproducing the observations. Deuterium prefers to partition into the water molecule over molecular hydrogen (H2), which preferentially takes ordinary hydrogen and escapes through the top of the atmosphere.

“This is the first published model that naturally replicates this data, giving us some confidence that the atmospheric evolution scenario we described matches early events on Mars,” Pahlevan said.

Aside from curiosity about early environments on planets, H2Rich atmospheres are important in the SETI Institute’s search for life beyond Earth. Experiments dating back to the mid-twentieth century show that prebiotic molecules involved in the origin of life readily form in such H2-rich atmospheres but not so easily in H2– poor (or more “oxidizing”) atmospheres. The implication is that early Mars was a hot version of modern Titan and a site at least as promising for the origin of life as early Earth was, if not more promising.


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More information:
Kaveh Pahlevan et al, A primordial atmospheric origin of hydrospheric deuterium enrichment on Mars, Earth and Planetary Science Letters (2022). DOI: 10.1016/j.epsl.2022.117772

Provided by the SETI Institute

Quote: New Clues to Mars’ Early Atmosphere Suggest Wet Planet Capable of Supporting Life (September 21, 2022) Retrieved September 22, 2022 from https://phys.org/news/2022-09-clues-early-atmosphere -mars-planet.html

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