Venus Chemistry & Climate Through Time

The past climate history of Venus remains a major unanswered question. Today, Venus is a hot, desiccated world with a thick atmosphere of 92 bar CO2. However, when it entered the runaway greenhouse state remains uncertain. Some previous works expect a runaway greenhouse immediately, and others have shown a 1 bar atmosphere could have hosted more temperature climates.

We have developed a comprehensive model of photochemistry, SO2 dissolution in water clouds, and climate to demonstrate that sulfuric acid hazes could have cooled early Venus.

SO2 dissolves in water droplets, but the majority of it reaches the stratosphere. There it becomes oxidized to sulfuric acid, which may condense to form hazes. These hazes are reflective (bright) and scatter incident sunlight away, cooling the climate.

We find atmospheres of 6-12% water vapor to have the brightest hazes. In this regime, the surface is cooled by the haze. Our model expects rain to reach the surface in these climates. A thin film of acidic liquid water may have been possible. However, too much water would gobble up the SO2 and prevent haze from forming, so there are important feedbacks regulating the SO2 chemistry and climate.

Venus likely hosted a steamier atmosphere at the time of the magma ocean, which would have been in a runaway greenhouse. As it lost its water, the climate may have transitioned to this cooler regime for a brief period of its history. As the world continued to lose its water, haze formation slowed and the climate likely transitioned into a runaway greenhouse again. The cartoon on the right shows this evolution track. The white contours are the stable greenhouse limits our model finds.

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