Astrophysicists led by the UNIGE and the NCCR PlanetS have traced the past of Venus to find out if Earth’s sister planet ever had oceans.
The planet Venus can be seen as Earth’s evil twin brother. At first glance, it is similar in mass and size to our home planet, is also largely made up of rocky material, contains some water, and has an atmosphere. But a closer look reveals striking differences between them: Venus’ thick CO2 atmosphere, extreme surface temperature and pressure, and sulfuric acid. pickles clouds are indeed a stark contrast to the conditions necessary for life on Earth. However, this may not always have been the case.
Previous studies have suggested that Venus may have been a much more hospitable place in the past, with its own oceans of liquid water. A team of astrophysicists led by the University of Geneva (UNIGE) and the National Center of Competence in Research (NCCR) PlanetS, Switzerland, examined whether our planet’s twin brother indeed had milder periods. The results, published in the journal Nature, suggest that this is not the case.
Venus has recently become an important research topic for astrophysicists. ESA and NASA have decided this year to send no less than three space exploration missions over the next ten years to the second closest planet to the sun. One of the main questions these missions aim to answer is whether Venus ever hosted early oceans. Astrophysicists led by Martin Turbet, researcher in the Astronomy Department of the Faculty of Science at UNIGE and a member of the NCCR PlanetS, have attempted to answer this question with the tools available on Earth.
“We simulated the climate of Earth and Venus at the beginning of their evolution, more than four billion years ago, when the planets’ surfaces were still molten,” explains Martin Turbet. “Due to the high temperatures involved, there might have been water in the form of steam, like in a giant pressure cooker.”
Using advanced three-dimensional models of the atmosphere, similar to those scientists use to simulate Earth’s current climate and future evolution, the team studied how the two planets’ atmospheres would evolve over time and whether oceans could form in the process.
“Thanks to our simulations, we were able to show that climatic conditions did not allow water vapor to condense in the atmosphere of Venus,” says Martin Turbet. This means that temperatures never got low enough for the water in the atmosphere to form raindrops that could fall on the surface. Instead, water remained in the atmosphere as a gas and oceans never formed. “One of the main reasons for this is the clouds that preferentially form on the night side of the planet. These clouds create a very powerful greenhouse effect that prevented Venus from cooling as quickly as previously thought,” the Geneva researcher continues.
Small differences with serious consequences
Surprisingly, the astrophysicists’ simulations also reveal that Earth could have easily suffered the same fate as Venus. If the Earth had been just a little closer to the sun, or if the sun had shone as brightly as it does today in its ‘youth’, our home planet would look very different today. It is probably the relatively weak radiation from the young sun that cooled the Earth enough to condense the water that makes up our oceans. For Emeline Bolmont, professor at UNIGE, member of PlaneS and co-author of the study, “This is a complete turning point in the way we look at what has long been called the ‘Faint Young Sun paradox’. It has always been considered a great obstacle to the appearance of life on Earth!” The argument was that if the sun’s radiation was much weaker than it is now, it would have turned the Earth into an ice ball hostile to life. “But it turns out that for the young, very hot Earth, this faint sun was actually an unexpected opportunity,” the researcher continues.
“Our results are based on theoretical models and are an important building block in answering the question of Venus’ history,” said study co-author David Ehrenreich, professor in UNIGE’s Department of Astronomy and member of the NCCR PlanetS. “But we won’t be able to make a final decision on our computers. The observations from the three future space missions from Venus will be essential to confirm – or disprove our work.” These prospects delight Emeline Bolmont, for whom “these fascinating questions can be answered by the new Center for Life in the Universe, which has just been established within the Faculty of Science at UNIGE.”
Reference: “Day-night cloud asymmetry prevents early oceans on Venus, but not on Earth” by Martin Turbet, Emeline Bolmont, Guillaume Chaverot, David Ehrenreich, Jérémy Leconte and Emmanuel Marcq, October 13, 2021, Nature.