Venus could always have been too hot for liquid water, emerges from a new model of its climate development. The results contradict earlier assessments, according to which the young Venus might once have owned seas. According to the new simulations, the cloud formation caused persistent steam boiler temperatures on the planet. The researchers admit that the data from planned space missions will only be able to clarify whether the Venus Oceans never actually existed, or whether they did.
It is the sister of earth and shares basic characteristics with our home planet: Venus also consists largely of rock material and has an atmosphere. Nevertheless, Earth and Venus differ like heaven and hell: The thick CO2 atmosphere of Venus causes extreme surface temperatures and high pressure. In addition, our neighbor is wrapped in caustic clouds of sulfuric acid. But Venus may not have always been as hostile to life as it is today. Earlier studies and climate models came to the conclusion that there might once have been conditions on Venus that allowed water vapor to condense and thus water to form on the surface. To test this hypothesis, the researchers led by Martin Turbet from the University of Geneva have now developed complex climate models again.
Climate history re-simulated
“We simulated the climate of Earth and Venus from the very beginning of their development – more than four billion years ago – when the surfaces of both planets were still molten,” explains Turbet. “The associated high temperatures meant that any water would have been in the form of steam, like in a gigantic pressure cooker.” With the help of complex three-dimensional models of the atmosphere, similar to those that scientists use to simulate the earth’s climate, the scientists then simulated how themselves the atmospheres of the two planets evolved over time and the extent to which oceans could have formed.
As they explain, a fundamental condition must have been met for the formation of seas: The temperature of the Venusian atmosphere should have dropped so far that water condensed and rained down for millennia – as happened on Earth. However, the researchers’ simulations showed that although the sun shone 30 percent less than it does today, this would not have been enough to lower the temperature of the young planet enough to meet this requirement. Otherwise, a corresponding temperature reduction could only have occurred if the surface of Venus had been shielded from solar radiation by clouds, say the scientists.
Clouds: warming instead of shielding?
However, according to the simulations, this was exactly the case – on the contrary: According to this, the clouds formed preferentially on the night side of Venus, where they could not shield the surface from solar radiation. Instead, they acted like a warm blanket there: the clouds helped maintain the high temperatures by creating a greenhouse effect that trapped the warmth in the planet’s dense atmosphere. “Ultimately, our simulations show that the climatic conditions did not allow water vapor to condense in the Venusian atmosphere,” summarizes Turbet. Instead, the water remained in the atmosphere as a gas and no oceans formed.
As the astrophysicists further report, their simulations also show that the earth could have suffered almost the same fate as Venus. If our planet were just a little closer to the sun or if it had shone as brightly in its youth as it does today, our home planet would look very different today. At that time it was probably only the relatively weak radiation that enabled the earth to cool down to such an extent that water condensed early on. “Possibly the weak sun was an opportunity for the young, very hot earth,” says Turbet. In the case of Venus, however, this level may never have occurred.
In conclusion, however, the co-author David Ehrenreich from the University of Geneva points out: “Although our results are important building blocks in answering the question about the history of Venus, they are based on theoretical models”. “The questions cannot be definitively answered with the help of computers,” says the scientist. But this year ESA and NASA decided to send three space missions to Venus over the next ten years. One of the most important goals is to use geological features to draw conclusions about whether the planet has ever hosted oceans or not. “Perhaps the observation data from these planned Venus space missions will confirm our results – or refute them,” says Ehrenreich.
Source: University of Geneva, CNRS, specialist article: Nature, doi: 10.1038 / s41586-021-03873-w