Venus has long been considered an almost-Earth. It is similar in size, has a dense atmosphere, and more and more studies point at a water-rich past. While this doesn’t imply the planet was habitable, it does suggest that water could be important in the evolution of rocky planets.
In a study published in the Journal of Geophysical Research Planets, researchers constructed detailed simulations of the impact of volatiles like water vapor and carbon dioxide on Earth-like planets. By changing the abundance of molecules as well as their distance from stars, the researchers were able to create a simple agorithm to forecast if a planet develops an ocean or not – and Venus could fit the bill.
Obviously, they don't mean today’s Venus. Venus is now a hellish place, with 90 atmospheres of pressure on its surface and an average temperature of 462°C (864°F). These conditions are the consequence of a dramatic runaway greenhouse effect. However, Venus was a lot different in the past.
According to the study, the properties of ancient Venus appear to be enough to allow for the formation of an ocean. Quite a significant ocean, in fact. To form it, the planet needed to have water vapor weighing about 30 percent of the Earth’s ocean.
The water vapor and carbon dioxide may have been liberated by the rock during a molten phase for the planet. As time passed, more gas escaped the rocks and the planet cooled. The cooling isn’t exactly linear, as the researchers had to take into account the energy a star would give to the planet, but it can be simplified by considering the distance of a planet from the star. That combined with the initial abundance of elements is what makes up the ocean recipe.
Other studies suggest that Venus might have kept an ocean up to 715 million years ago, although that is also based on simulations. We currently don’t have observations strongly supporting this hypothesis.
Venus' cloud cover is too thick for direct imaging and radar observations of its surface are also not helpful since strong volcanic events have reshaped it completely. More work will be necessary to confirm the existence of an ocean. Still, maybe billions of years ago, Venus, Earth, and Mars all looked quite blue with water.
