An interaction that is absent in the Earth's atmosphere, but typical of the ancient Martian, may provide an answer to the question of the mysteriously high temperature on Mars in the past.
Scientists from the United States have analyzed the reasons for the paradoxically warm climate on ancient Mars in the era of the existence of open reservoirs there. According to their calculations, all previous work did not take into account the importance of the interaction of carbon dioxide and methane with each other. This unaccounted factor in Martian conditions could give a greenhouse effect much greater than previously assumed. The new work also shows that modern ideas about the outer border of the habitable zone were wrong: planets with atmospheres of the same type as ancient Mars can be habitable, even if this is impossible according to modern views. A related article was published in Geophysical Research Letters.
In recent years, evidence has emerged that ancient Mars had liquid water and possibly full oceans, even 4 billion years ago, when the Sun was nearly 30 percent dimmer today. Mars, both then and now, receives from the Sun 2.5 times less light than the Earth. This means that 4 billion years ago he received 3.5 times less heat from our star.
Simple calculations show that if the Earth is heated at least twice weaker, there will be no liquid water on it at all. And even if Mars in ancient times had a carbon dioxide atmosphere hundreds of times denser than today, it would still be too cold for open bodies of water.
The authors of the new work note that this means that all existing models of ancient Mars do not radically take into account something. Researchers have performed calculations of how the collisions of carbon dioxide and methane molecules change the probability of their absorption of photons. According to their data, it turned out that the probability of blocking photons in this case is many times higher than in atmospheres consisting only of carbon dioxide or only methane.
Any realistic calculations of the gas shell of Mars in ancient times are based on atmospheric pressure no higher than 1.5-2 units of the modern earth pressure. A denser atmosphere with weaker Martian gravity would be difficult to contain. The two-gas atmosphere retains heat much better than previously thought possible for such a moderate pressure range. Until now, no one has taken into account this possibility simply because in the Earth's atmosphere both methane and carbon dioxide are contained in very small quantities and the interaction between their molecules is unlikely here.
The model, where carbon dioxide is 90 percent, and methane and its decay products are 5–10 percent, rather quickly showed the authors of the work that the greenhouse effect in this scenario is much stronger than previously thought. He could heat Mars to zero degrees Celsius, even with the weak sunlight that fell then on the Red Planet.
The researchers note that a similar interaction between carbon dioxide and methane can heat the planet to high temperatures, which are now considered to be outside the habitable zone. So, today Mars is located on the outer border of the habitable zone. But 4 billion years ago, it seems to have been far beyond its borders. New work shows that the farthest inhabited planetary orbit may be 12-13 percent farther from the star than previously thought. Accordingly, many exoplanets, today regarded as too cold for life, are potentially quite suitable for life - at least for anaerobic one.
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