Researchers from the Department of Geosciences at the University of Chicago have built a new model for the composition of Venus’s atmosphere, suggesting that Venus may have had liquid water in the past. The scientists’ results were published in Proceedings of the National Academy of Sciences.
Water is found throughout our solar system, usually in the form of ice or atmospheric gas, although sometimes in liquid form. All the planets, many moons, from the inner asteroid ring to the Kuiper ice belt to the distant Oort cloud, two light years away, have water.
Venus is a hot, dry, rocky planet, slightly smaller than ours, with only trace amounts of water vapor in a thick CO2 atmosphere, and previous studies have attempted to model its atmospheric past. Depending on how past models were built, completely different climate patterns emerge.
On the one hand, many models argue that Venus may have always been an uninhabitable hot mess with no liquid water on its surface. The ever-increasing amount of CO2 in the atmosphere wrapped the planet in a thick, heavy blanket, resulting in a current atmospheric pressure on the surface 92 times that of Earth, making Venus hotter than Mercury. Even icy comets hitting Venus would not be enough to keep water on the surface.
On the other hand, there are models that suggest that in the early solar system, when solar radiation was 30% less, Venus could have had a moderate surface temperature with a much thinner atmosphere and masses of liquid water on its surface – perhaps oceans – another 700 million years ago, before the runaway greenhouse effect evaporated it.
Researchers from the University of Chicago decided to solve this issue using their own model. They took a unique approach: they first hypothesized that there once was an ocean with a habitable climate by filling in a computer model with many different ocean levels and running those oceans through three different processes of evaporation and removal of oxygen. They ran the model with three different time-dependent starting points a total of 94,080 times, with a scoring system that allowed them to identify runs with results closest to the actual Venusian atmosphere at present.
Out of 94,080 launches, only a few hundred were within range of the actual Venusian atmosphere that we see today, according to a study published in PNAS. Hypothetical habitable epochs on Venus should have ended before 3 billion years ago with a maximum ocean depth of 300 meters over its entire surface (total hydrosphere).
The results show that Venus has been uninhabited for over 70% of its history, four times longer than some previous estimates. If there really was liquid water on the surface of Venus 3 billion years ago, it could also have life on it.
Source: Alexandra O. Warren et al, Narrow range of early habitable Venus scenarios permitted by modeling of oxygen loss and radiogenic argon degassing, Proceedings of the National Academy of Sciences (2023). DOI: 10.1073/pnas.2209751120