With a temperature of about 500 degrees Celsius, the surface of Venus is hostile to life – but the higher temperatures in the planet’s atmosphere are much lower. Could microorganisms colonize this area? My research team has now answered this question with a resounding refusal. According to scientists in the journal Nature Astronomy, there is not enough water for life. Mars offers better prospects. Lakes on the Red Planet have not only provided sparse conditions, but have also been life-friendly for millions of years, a second team also reports in “Nature Astronomy.”
Only recently has the supposed discovery of phosphine gas in the atmosphere of Venus sparked discussions about life on the planet. “However, research on this matter has so far overlooked the role of aquatic activity in ecological livability,” explain John Halsworth of Queen’s University Belfast and colleagues. Biologists use water activity to describe the proportion of unconstrained water, that is, water that is available for life processes. This value can range from 0 to 1, but life is only possible if the water activity is greater than 0.585.
Hallsworth and his team have now analyzed conditions in the highly volatile region of Venus’s atmosphere. It turns out that the value of water activity in this area is less than 0.004 – water is rarely available for life there. According to scientists, this is caused by large amounts of sulfuric acid droplets. This means that there are no microbes there.
The situation is different with Mars: Hallsworth and colleagues have determined a water activity of 0.537 for its thin atmosphere — just below the limit allowed for a life-friendly environment. Since the climate on the Red Planet has changed dramatically during its history, the atmosphere may have been more favorable for life in the past.
This is also supported by the findings of a study by Elizabeth Lusa Adams and colleagues from the University of Vigo in Spain. The team analyzed X-ray measurements taken by the Curiosity rover on sediment deposits in Gale crater. Curiosity has been traveling in this Martian crater since 2012, where there was a lake in the early days of Mars. “Until now, we did not know whether the sediments were formed by the slow process of deposition or by short-term selective floods,” Losa-Adams and colleagues explain.
With the help of X-ray measurements, the researchers were able to examine the crystalline structure of the sediment and learn how it was deposited. Their finding: The sediment must have been deposited in calm waters over a long period of time. So the lake in Gale Crater was not a short-lived body of water, but rather provided life-friendly conditions for a much longer period of time – perhaps up to ten million years. The temperatures should also have been suitable for the emergence of life during this epoch, because the water did not freeze into ice and did not evaporate very quickly. Unlike the atmosphere of Venus, it is possible that life may have arisen in the water-rich environment of the young planet Mars.
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