Venus might not have always been Earth’s evil twin. Simulations suggest that before the crushing winds, acidic atmosphere and scorching heat set in, our rocky neighbor may have been capable of supporting life. The range of conditions necessary for such a scenario are limited though, so scientists don’t think that we should expect to find a fossil record there, but the possibility of a habitable Venus has implications for how we search for life-supporting exo-planets in other solar systems.
We’re pretty confident that Venus has gotten hotter over the years. Even though it’s 25 million miles closer to the Sun than Earth, and thus receives twice as much solar energy as us, its current surface temperature of 864° Fahrenheit is thanks to the heat being trapped by the planet’s thick atmosphere. Things probably weren’t so bad a few billion years ago, especially if Venus had the same rotational speed, plus a decently-sized ocean. That combination would have meant that the planet could have had an average temperature of only 51° Fahrenheit 2.9 billion years ago, warming up to a modest 59° after around 2 billion years of warming.
For this more tepid version of Venus to work, the slow rotational speed of the planet would need to be intact the whole time. It takes 243 Earth days for Venus to rotate once, which would let clouds amass on the sunny side of the planet, acting like a big heat shield. The clear skies on the dark side would allow for some much needed venting, keeping temperatures from rising too high. If clouds couldn’t be built up in this way, because the oceans weren’t present, or the planet rotated faster in the past, then this scenario wouldn’t come together.
A new template for temperate planets
These simulations are more than just thought exercises in how atmospheres affect temperatures. Venus is on what’s considered to be the inner boundary of our solar system’s habitable zone, and thus similar planets in other systems may have been overlooked when looking for water-friendly, life-sustaining environments. These findings show how a pleasant ocean could exist on exo-planets at a similar distances from their stars, at least under specific parameters.
Source: Hellish Venus Might Have Been Habitable for Billions of Years by Shannon Hall, Scientific American