The researchers also determined that a similar story could also have played out on Earth if things had been a little different.
Venus, our closest planetary neighbor, is called Earth’s twin because of the similarity in size and density of the two planets. Otherwise, the planets are radically different.
While Earth is a natural hub for life, Venus is a lifeless planet with a toxic carbon dioxide atmosphere 90 times thicker than ours, clouds of sulfuric acid, and surface temperatures. reaching 864 degrees Fahrenheit (462 degrees Celsius) – hot enough to melt lead.
To understand how these two rocky planets evolved so differently, a team of astrophysicists decided to try and simulate the beginning, when the planets in our solar system formed 4.5 billion years ago.
They used climate models – similar to those researchers use to simulate climate change on Earth – to go back in time to young Venus and Earth.
When Earth and Venus were furnaces
Over 4 billion years ago, the Earth and Venus were very hot and covered with magma.
Oceans can only form when temperatures are cold enough for water to condense and fall as rain for thousands of years. This is how the Earth’s global ocean formed over tens of millions of years. Venus, on the other hand, remained warm.
Back then, our sun was about 25% weaker than it is today. But that wouldn’t have been enough to help Venus cool off, as it is the second closest planet to the sun. The researchers wondered if clouds could have played a role in helping Venus cool.
Their climate model determined that clouds contributed to it, but in an unexpected way. They regrouped on the night side of Venus where they could not have protected the day side of the planet from the sun. Although Venus is not locked in relation to the sun, where one side of the planet still faces the star, its speed of rotation is extremely slow.
Rather than shielding Venus from the heat, the clouds on the night side contributed to a greenhouse effect that trapped heat in the planet’s dense atmosphere and kept temperatures high. With such constant and trapped heat, Venus would have been too hot for the rain to fall. Instead, water could only exist in its gaseous form, water vapor, in the atmosphere.
“The associated high temperatures meant that any water would have been present in vapor form, like in a gigantic pressure cooker,” said Martin Turbet, lead author of the study, a researcher in the Department of Astronomy at the Faculty of Science and Technology. ‘University of Geneva. member of the National Center of Competence in Research PlanetS, Switzerland, in a press release.
Why the Earth could have followed the same path
Things could have turned out the same for Earth if our planet had been slightly closer to the sun or if the sun was as bright then as it is now.
Because the sun was weaker billions of years ago, the Earth was able to cool enough from its molten state for water to form and create our global ocean. The weak young sun “was a key ingredient in forming the first oceans on Earth,” Turbet wrote in an email.
“It’s a complete reversal in the way we look at what has long been called the ‘young pale sun paradox’,” said Emeline Bolmont, co-author of the study and professor at the University of Geneva, in a press release. “It has always been considered a major obstacle to the appearance of life on Earth. But it turns out that for the young and very hot Earth, this weak Sun could in fact be an unexpected opportunity.”
Previously, scientists believed that if solar radiation was weaker billions of years ago, the Earth would have turned into a snowball. Instead, the opposite was true.
The results show the variety of ways rocky planets evolved in our solar system.
The terrestrial ocean has existed for almost 4 billion years. There is evidence that Mars was covered with rivers and lakes between 3.5 and 3.8 billion years ago. And now, it seems less likely that Venus was ever able to withstand liquid water on its surface.
Beyond our solar system
The new research could also be applied to exoplanets (planets outside our solar system).
“Our results have strong implications for exoplanets, as they suggest that a large portion of the exoplanets that were thought to be capable of having surface oceans of liquid water are probably now parched because they never managed to condense and thus form their first oceans, ”he added. said Turbet.
Future missions to Venus can help test the theory put forward by Turbet and his team.
“Our results are based on theoretical models and are an important part of answering this question,” he said. “But observations are needed to definitively settle the question! Hopefully future EnVision, VERITAS and DAVINCI + space missions will give us a definitive answer.”
These NASA and European Space Agency missions, slated to launch at the end of the decade, will help scientists understand the oldest surface features of Venus called tesserae, which “may contain evidence of past traces. of the presence (or absence) of liquid water on the surface of Venus, ”Turbet said.