Let’s be honest: There’s really no good place for humans in the Solar System that isn’t Earth. But that doesn’t mean that all bad places were created equal; And Venus is about as inaccessible as a temperate-zone rocky exoplanet can get.
In recent years, there has been increasing evidence to suggest that this was not always the case. That, at one time, in its wild, wayward youth, Venus may have been habitable with a beautiful climate and even liquid oceans.
Well, maybe we should forget all that. Earth’s so-called sister planet never cooled enough to allow the condensation of water into liquid, according to new research modeling the climates of Venus and Earth in its early years.
Once a poisonous hell-planet, always a poisonous hell-planet, it seems.
Venus is similar to Earth in many ways. It is a similar size and composition, and once, when the Sun was younger and cooler, its climate should have been more temperate.
Now, it is anything but temperate. The sky of Venus is filled with thick clouds of sulfuric acid, and its atmospheric pressure at altitude 0 is about 100 times greater than that of Earth. If that weren’t bad enough, this lander is melting hot, with an average surface temperature of 471 °C (880 °F).
But because of the resemblance between the two planets, scientists think Venus may be a sign of what Earth’s future holds, as the Sun’s luminosity continues to increase.
This is especially relevant if Venus was once again Earth-like with liquid oceans, and previous research has found evidence that this could have been the case, especially when the Sun is about 30 percent dimmer than today (and so it was cold).
This faint, young Sun, however, presents a paradox: At those temperatures, Earth should have been a frozen ice ball, yet we have evidence that liquid water was present relatively earlier.
A team of ice researchers by astronomer Martin Turbet of the University of Geneva in Switzerland has now not only shown that Venus was never Earth-like, but found a resolution for the faint, young Sun paradox.
“We simulated the climates of Earth and Venus at the beginning of their evolution, 4 billion years ago, when the planet’s surface was still molten,” Turbett said. “The associated high temperature meant that any water would exist as steam, as in a giant pressure cooker.”
For this steam to condense into clouds and rain on the surface, Venus must have cooled for several thousand years. This could have happened only if clouds formed to block solar radiation from the surface of Venus.
The team’s climate modeling has shown that clouds may form on the child of Venus – but only on the cold night side of the planet. Not only does this block solar radiation from reaching the day side, but it also makes the planet warmer by producing a powerful greenhouse effect on the night side.
This would mean that water vapor could never have condensed in the atmosphere, let alone enough to rain down on the planet to fill entire oceans for millennia. This validates the notion of a “Steam Venus” that was first proposed in 2013 using simple modeling.
Interestingly, however, the team’s work showed that there could have been a “Steam Earth” even with a weaker Sun. In fact, if solar radiation was more powerful, Earth could end up like Venus.
Instead of freezing a liquid Earth, research has shown that the faint young Sun may have allowed our steamy planet to cool enough that water could condense into a liquid.
Exactly how Earth and Venus ended up on such different evolutionary paths is far from confirmed, and is a mystery planetary scientists would love to solve. Even if it has no implications for our future, it could help us find other habitable worlds, out there in the wider Milky Way.
“Our results are based on theoretical models and are an important building-block in answering the question of the history of Venus,” said astronomer David Ehrenreich of the University of Geneva.
“But we won’t be able to rule the matter definitively on our computers. Observations from three future Venusian space missions will be necessary to confirm or refute our work.”
research has been published in Nature.