Venus

Venus May Have Been Just Like Earth For BIllions Of Years

The temperatures on Venus are hot enough to melt lead, and its winds have been known to blow 60 times faster that the planet rotates. Though it may be hellish today, Venus probably wasn't always such a scorching hot mess. In fact, scientists now believe that Earth's sister planet may have been habitable for billions of years.

Related: The Sun Will One Day Consume Mercury And Venus

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Mild Weather Today, With Volcanoes Later

Venus and Earth are similar in size and density, and about 2.9 billion years ago, they were more similar in climate too. Michael Way of NASA's Goddard Institute for Space Studies and his team made this discovery after they applied the first three-dimensional climate model to an early Venus—a model that uses the same computer simulations used to predict human-caused climate change on our planet. They found that about 2.9 billion years ago, Venus had a cool climate that hovered around 51° F (11° C). Pushing the clock forward to 719 billion years ago, Venus' climate only rose to around 59° F (15° C). The planet was likely able to stay cool and maintain liquid oceans for so long because of clouds, which shielded the planet from incoming sunlight.

Related: The Harsh Conditions of Venus, Earth's Sister Planet

A Runaway Greenhouse Effect

So what happened? Why did Venus's weather change from a fall day in London to summer vacation in Hades? It turns out that although the planet's position close to the sun wasn't a problem early on, the sun eventually got hotter. As stars age, they get denser, which increases their pressure and thereby boosts their temperature. As a result, our own sun shines about 30 percent hotter and brighter than it did at its birth 4.5 billion years ago. The rising heat of the sun gradually drove its water into space, leaving behind carbon dioxide in its wake. Carbon dioxide, as we know too well here on Earth, is a potent greenhouse gas—that is, it captures the planet's heat before it can escape into space, thereby warming the atmosphere. As the planet got hotter, it drove more carbon dioxide out of the surface rocks in a vicious cycle that scientists refer to as a runaway greenhouse effect.

Related: Cow Burps Are Helping To Cause Climate Change

Carbon dioxide levels are rising on our planet, too. While most scientists have historically believed that a runaway greenhouse effect was impossible on Earth because we have water vapor to protect us, a 2013 study says that it might happen more easily than we thought. The good news is that the study authors don't believe human influences are enough to create the right conditions. Still, as Carl Sagan wrote in the book Cosmos, "The surface environment of Venus is a warning: something disastrous can happen to a planet rather like our own."

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