Mars could have been warm and wet while Earth was still a glowing ball of molten rock

Since the 1970s, continued exploration of Mars has shown that the planet had an extremely interesting history. While conditions there are not livable today, scientists know that Mars was once a much warmer, wetter place, with flowing water on its surface. Mars may have been a “pale blue dot” covered in oceans while Earth was still a sphere of slowly cooling molten rock, according to new research led by the University of Arizona (UoA). This discovery could enable new research into a previously overlooked period in the geological history of Mars and the formation and evolution of the solar system.

The team was led by Kaveh Pahlevan, a research scientist 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, Regents’ Professor at SESE and ASU School of Molecular Sciences (SMS).

The paper 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 robotic orbiters, landers, and rovers, scientists have determined that about 4.2 to 3.7 billion years ago, Mars began to move from a warmer, wetter planet to the extremely cold one and dry environment that we see there today. However, unanswered questions remain about how long liquid water flowed on the surface of Mars and whether it was intermittent or constant.

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primordial atmosphere of Mars

To answer this question, astronomers have tried to reconstruct what the atmosphere of Mars looked like billions of years ago. A popular method used by Mars missions is to collect samples and analyze them for their deuterium to hydrogen (D/H or D/H) ratio ²H/¹H) or the number of deuterium atoms in a sample divided by the number of normal hydrogen atoms. This method allows scientists to measure the prevalence over time of molecular hydrogen (H) in the Martian atmosphere, which is a potent greenhouse gas. As Prof. Desch said in an ASU press release:

“It is paradoxical that so many observations point to liquid water on early Mars, even though the water on present-day Mars is frozen and the ancient Sun was 30% dimmer than it is today. Traditionally considered greenhouse gases like CO2 would freeze on early Mars. Hydrogen in the atmosphere is an unexpected way to stabilize liquid water.”

For their study, the team developed the first model of primordial atmospheric evolution on Mars, which included high-temperature processes associated with different geological periods. These included the formation of Mars, the time 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 escaping from the molten rock were a mixture of molecular hydrogen and water vapor, and that Mars’ earliest atmosphere was much denser than it is today.

Their model also showed that water vapor in the Martian atmosphere behaved much like it does in Earth’s atmosphere today. Essentially, it would condense as clouds in the lower atmosphere while very little is retained in the upper atmosphere. Meanwhile, the 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 may have had warm-water (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. like dr Pahlvan explained:

“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, specifically the Mars Science Laboratory’s Curiosity rover.” 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.”

impact on life

The results agree with the clay samples obtained from NASA Curious Rover revealed something about the Hesperian era (c. 3.7 – 2.9 billion years ago) and corroborated what previous studies of Martian meteorites had shown. Martian meteors are composed largely of igneous (ie, volcanic) rock that formed inside Mars and was expelled by magma rising to the surface. These meteors contain dissolved water inside and have been found to have similar D/H ratios to Earth’s oceans. This shows that Earth and Mars drew their water from the same source during the early solar system.

In addition, those of Dr. Studies conducted by Pahlevan and his colleagues show that if the original Martian atmosphere were dense and hydrogen-rich, the surface water would have been naturally enriched in deuterium by a factor of two to three compared to the interior. This is what the clay samples from the Hesperian era have preserved curiosity showed what corresponds to 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 time Mars formed (about 4.5 billion years ago) and the Hesperian era.

As a heavier element, deuterium was lost more slowly, leading to the observed enrichment in surface water. These findings could also have implications for the ongoing search for evidence of past life on Mars (which may still exist underground today). These include the Stanley Miller experiments of the mid-20th century, which showed that prebiotic molecules form more easily in hydrogen-rich “reducing” atmospheres than in “oxidizing” atmospheres – like those on Earth and Mars today.

In recent years, planetary scientists have also shown that atmospheric hydrogen can play a crucial role in habitability and expand a planet’s habitable zone. These results suggest that ancient Mars had an environment as amenable to early life as Earth. Perhaps even more so, since 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.

Further reading: ASU