Since the 1970s, continued exploration of Mars has revealed that the planet has had a most interesting history. Although conditions there are not suitable for life today, scientists know that Mars was once a much warmer and wetter place, with water flowing over its surface. According to new research from the University of Arizona (UoA), Mars could have been a “pale blue dot” covered in oceans while Earth was still a slowly cooling ball of molten rock. This discovery could allow new research on a hitherto unknown period of the geological history of Mars and on the formation and evolution of the solar system.
The team was led by Kaveh Pahlevan, a researcher at ASU’s School of Earth & Space Exploration (SESE) and the Carl Sagan Center SETI Institute. He was joined by Laura Schaefer, assistant professor of geological sciences at Stanford University; Linda T. Elkins-Tanton, professor of planetary sciences and director of SESE at ASU; SESE professor of astrophysics Steven J. Desch and ASU-SESE; and Peter R. Buseck, full professor at SESE and ASU School of Molecular Sciences (SMS).
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The article describing their findings, titled “A primordial atmospheric origin of hydrospheric deuterium enrichment on Mars”, appeared in the October 1 issue of the Earth and Planetary Science Letters. Based on multiple lines of evidence obtained from orbiters, landers and robotic rovers, scientists have established that around 4.2 to 3.7 billion years ago, Mars began to transition from a warmer and more humid planet with the extremely cold and dry environment that we see there today. However, there remain unanswered questions about how long liquid water flowed on the surface of Mars and whether it was intermittent or constant.
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Mars Primordial Atmosphere
To answer this question, astronomers have attempted to reconstruct the atmosphere of Mars billions of years ago. A popular method used by Mars missions is to collect samples and analyze them for their deuterium-hydrogen ratios (D/H or 2H/1H), or the number of deuterium atoms in a sample divided by the number of normal hydrogen atoms. This method allows scientists to assess the prevalence of molecular hydrogen (H) in the Martian atmosphere over time, which is a potent greenhouse gas. As Professor Desch said in an ASU press release:
“It’s a paradox that so many observations suggest liquid water in early Mars, even though water is freezing on today’s Mars, and the ancient sun was 30% dimmer than today. today. The greenhouse gases traditionally thought of as CO2 would freeze on an early Mars. Hydrogen in the atmosphere is an unexpected way to stabilize liquid water.
For the purposes of their study, the team developed the first model of primordial atmospheric evolution on Mars that included high-temperature processes associated with different geological periods. This included the formation of Mars, when its surface was covered by an ocean of magma, and the formation of the first oceans and atmosphere. These models showed that the main gases emerging from the molten rock were a mixture of molecular hydrogen and water vapor and that Mars’ early atmosphere was much denser than it is today.
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Their model also showed that water vapor in the Martian atmosphere behaved similarly to how it behaves in Earth’s atmosphere today. Essentially, it would condense in the lower atmosphere as clouds, while very little was retained in the upper atmosphere. During this time, molecular hydrogen (the main component of the atmosphere) did not condense and was slowly lost to space. They further calculated that the molecular hydrogen content of the atmosphere would have a significant greenhouse effect, to the point that Mars could have had warm (or even hot) water oceans.
These oceans were stable and would have remained on the surface of Mars for many eons before atmospheric hydrogen was gradually lost to space. As Dr. Pahlevan explained:
“This key idea – that water vapor condenses and is retained on early Mars whereas molecular hydrogen does not condense and can escape – allows the model to be directly linked to measurements made by spacecraft. , in particular the Mars Science Laboratory’s Curiosity rover. This is the first model that naturally reproduces these observations, giving us some confidence that the evolutionary scenario we have described corresponds to the first events on Mars.
Implications for life
The results are consistent with clay samples obtained by NASA Curiosity Rover revealed about the Hesperian era (about 3.7 to 2.9 billion years ago) and reinforced what previous studies of Martian meteorites had shown. Martian meteors are composed largely of igneous (i.e. volcanic) rock that formed inside Mars and was ejected by magma rising to the surface. These meteors contain dissolved water inside and have D/H ratios similar to those of Earth’s oceans. This shows that Earth and Mars drew their water from the same source at the start of the solar system.
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Additionally, research by Dr. Pahlevan and his colleagues has shown that if the primordial Martian atmosphere was dense and hydrogen-rich, surface waters would have been naturally enriched in deuterium by a factor of two to three relative to the atmosphere. inside. This is what the clay samples from the Hesperian period obtained by Curiosity shown, which was a D/H value about three times that of Earth’s oceans. The only explanation is that molecular hydrogen was lost to space between the period when Mars was still forming (about 4.5 billion years ago) and the Hesperian era.
As the heaviest element, deuterium was lost at a slower rate, leading to the observed levels of enrichment in surface waters. These findings could also have implications in the ongoing search for evidence of past life on Mars (which may still exist underground today). These include the Stanley-Miller experiments from the mid-twentieth century, which showed that prebiotic molecules form more easily in “reducing” hydrogen-rich atmospheres than in “oxidizing” atmospheres – such as those in the Earth and Mars today.
In recent years, planetary scientists have also shown that atmospheric hydrogen can play a critical role in habitability and extend a planet’s habitable zone. These findings suggest that ancient Mars had an environment just as conducive to early life as Earth. Perhaps even more, since the Earth only fully formed after the massive impact that formed the Moon (Theia) 4.5 billion years ago. While the Earth-Moon system was still covered in molten magma, Mars had a dense atmosphere, warm temperatures, and a surface covered in blue oceans.
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