Due to its size, Venus is called Earth's twin, but that’s where the similarities end. Venus is a hellish world of lead-melting temperatures, crushing atmospheric pressures, and acid clouds. Astronomers have wondered if the planets may have been similar in the past. A new study suggests that this is unlikely.
In a paper published in Nature, astronomers suggest that Venus never got cool enough to form oceans. Venus and Earth were literally worlds apart from the very beginning. The team of researchers used sophisticated climate simulations to work this out.
The models started with a planet with a molten surface, like Earth and Venus billions of years ago, which allowed scientists to follow its evolution, such as the formation of clouds on the planet's nightside. Earth did eventually cool down and turn into the world we know. On Venus, on the other hand, the water remained as steam in the atmosphere never raining down on the planet.
“Thanks to our simulations, we were able to show that the climatic conditions did not allow water vapor to condense in the atmosphere of Venus,” lead author Dr Martin Turbet from the University of Geneva (UNIGE), stated. “One of the main reasons for this is the clouds that form preferentially on the night side of the planet. These clouds cause a very powerful greenhouse effect that prevented Venus from cooling as quickly as previously thought.”
The study also explains how Earth stayed warm during its formative years. The Sun was a lot weaker in the past, something that had researchers wondering why our planet wasn’t just a frozen rock. The clouds actually helped; a hotter Sun would have turned Earth into something like Venus.
“This is a complete reversal in the way we look at what has long been called the ‘Faint Young Sun paradox'. It has always been considered as a major obstacle to the appearance of life on Earth,” Emeline Bolmont, professor at UNIGE and co-author of the study, added.
While the simulation is a compelling explanation for why the two planets differ so much, this is not the final word on the matter. More data is needed to understand the full history of Venus. Luckily, there are three missions going back there in the next decade: two from NASA and one from the European Space Agency. Possibly four since the UAE threw its hat in the ring.
“Our results are based on theoretical models and are an important building-block in answering the question of the history of Venus,” explained co-author David Ehrenreich, professor at UNIGE. “But we will not be able to rule on the matter definitively on our computers. The observations of the three future Venusian space missions will be essential to confirm – or refute – our work.”