With Venus, discoveries are often combined in the conditions. Contrary to a scenario proposed a few years ago, the planet we want to call the “twin” of the Earth has never been able to meet oceans, according to astrophysicist and climatologist Martin Turbet, of the University’s Astronomical Observatory. of Geneva, associated with a team of scientists from her university and from the astrophysics laboratories of Bordeaux and Latmos, specialized in the sphere. “We have probably underestimated the difficulty needed to make oceans appear on planets like Earth or Venus or even exoplanets,” he said. Here are some benchmarks to understand what we are talking about, and what such a statement means.
What do we know about Venus?
Not much, and that’s the problem. Thanks to probes and reconnaissance, we now know that Mars protected large water bodies. But on Venus, the colossal pressure and infernal temperature of more than 470 degrees Celsius that reigned there soon got the better of the rare probes that landed there. Hidden by thick clouds of sulfuric acid droplets, the surface of Venus remains largely a mystery. However, a landmark 2016 study questioned whether Venus could have been habitable, assuming that its cloud cap would have long protected hypothetical aquatic life. A scenario completely in doubt by this new study published in Nature.
Why does the ocean hypothesis no longer hold true?
“Before we ask how an ocean can be stable on the surface of Venus, we need to ask how it could be formed,” says Martin Turbet. We must therefore investigate how, a few billion years ago, we went from a “very young, very hot” planet, where all the available water was “in the atmosphere in the form of vapor”, to a planet, where by condensation by cooling, steam could have formed oceans. His team used a sophisticated climate model, taking into account cloud formation and atmospheric circulation. Its conclusions are definitive.
The sun heated the water vapor in the atmosphere of Venus to too high a temperature to form clouds by condensation. Clouds that, by protecting the sunny side of the planet, could have cooled their atmosphere to cause the condensation of their water vapor and thus form oceans. Increasing conditions, the air masses heated by the sun, on the ‘day’ side, have moved to the night side of the planet. There they formed clouds at high altitudes, causing a greenhouse effect that prevented the cooling of Venus’ atmosphere.
How did the earth escape this sad fate?
Because, “when the sun was younger, four billion years ago, it was 25 to 30% less bright compared to today,” Martin Turbet explains. The heat with which it flooded our planet was then low enough to allow condensation of water vapor and the formation of oceans. Venus, much closer to the Sun, at that time had an insulation of about double, too high to make such a phenomenon possible. A sun just a little warmer a few billion years ago would have prevented the appearance of oceans and probably life.
What does that change in our knowledge of Venus?
The climate model thus developed will be used for the study of exoplanets, which belong to other solar systems. Meanwhile, for Venus, it complicates the scenario of an appearance of life. A study released last year reported the discovery, in the clouds, of a gas that may have been linked to living things. They imagined that an evaporation of the oceans on the planet would have migrated some form of life into these clouds. Several studies refuted these observations, for another, last June, considered any form of life in these clouds impossible, due to lack of enough water to support it.