The first history of Mars shows that the red planet was born wet

Earth and Planetary Science Letters reports that Mars’ rich atmosphere has allowed warm to warm waters for millions of years. To achieve this, astronomers built the first model in the history of the Martian atmosphere that links the fused origin of Mars to the formation of the first oceans and the atmosphere.

This model indicates that, as on Earth, the water vapor in the Martian atmosphere was concentrated in the lower atmosphere and that the upper atmosphere of Mars was “dry” because the water vapor condensed as clouds at lower altitudes. Molecular hydrogen (H2), on the other hand, did not condense.

Instead, it moved into Mars’ upper atmosphere and was lost in space. This discovery – that water vapor condensed and was retained on early Mars – allows the model to be linked directly to measurements from spacecraft, most notably the Mars Science Laboratory’s Curiosity rover.

The researchers think they modeled a neglected period in the early history of Mars, just after the planet was formed. Kaveh Pahlevan, a researcher at the SETI Institute, said: “To explain the data, the early Martian atmosphere had to be very dense (more than ~ 1000 times denser than the modern atmosphere) and composed mainly of molecular hydrogen (H2). . ”

This finding is significant as it is well known that H2 is a potent greenhouse gas in rather dense environments. The very first oceans with warm to warm water would have been able to remain stable on the Martian surface for millions of years until H2 was progressively lost to space thanks to the high greenhouse effect of this atmosphere.

The very first oceans with warm to warm water would have been able to remain stable on the Martian surface for millions of years until H2 was progressively lost to space thanks to the high greenhouse effect of this atmosphere.

The model is limited by the deuterium-hydrogen (D / H) ratio of several Martian samples, such as meteorites and those analyzed by Curiosity. Deuterium is a heavy form of hydrogen. Mars meteorites are mainly igneous rocks, having been created when magma rose from deep within the Martian crust to the outer layers of the planet.

The deuterium-hydrogen ratio of the dissolved water in these internal igneous rocks (derived from the mantle) is comparable to that of the oceans on Earth, suggesting that the two planets initially had identical D / H ratios and that their water came from the same source in the first Solar System.

On the other hand, Curiosity measured the D / H ratio of the 3 billion-year-old clay on the surface of Mars and found that it is about three times that of the oceans on Earth.

It appears that the hydrosphere, Mars’ surface water reservoir, had significantly concentrated deuterium in relation to hydrogen when these ancient clays formed. This amount of enrichment (or concentration) of deuterium can only be achieved by preferentially losing the lightest H isotope into space.

The model also demonstrates that if the Martian atmosphere was rich in H2 during its origin (and over 1000 times the density today), surface waters would naturally be enriched in deuterium by a factor of 2-3x compared to the interior, reproducing the results.

Unlike molecular hydrogen (H2), which preferentially absorbs normal hydrogen and escapes from the upper atmosphere, deuterium prefers partitioning in the water molecule.

“This is the first published model that naturally reproduces this data, giving us some confidence that the atmospheric evolutionary scenario we described corresponds to the first events on Mars,” Pahlevan added.

H2-rich atmospheres play a crucial role in the SETI Institute’s research for extraterrestrial life, aside from human interest in early habitats on planets.

Early life-bound prebiotic molecules can form rapidly in H2-rich atmospheres, according to experiments dating back to the mid-20th century, but not as easily in H2-poor (or more “oxidizing”) atmospheres.

The bottom line is that the first Mars was a heated counterpart to the current Titan and a site for the birth of life that was at least as favorable as early Earth, if not more promising.

Source: doi.org/10.1016/j.epsl.2022.117772

Image credit: Getty

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