Oceans on Venus May Never Have Existed

Despite the hopes of both astronomers and sci-fi fans alike, Venus may never have been habitable to life. This is the conclusion of a new study out of the University of Cambridge, which has been published in the journal Nature Astronomy. The surface of Venus is currently a sweltering furnace, with average temperatures of 867 degrees F, an atmosphere made of mostly CO₂, and a surface pressure about 92 times that of Earth's. Yet the planet has been long theorized to have been habitable many millions of years ago, with oceans of liquid water. According to the researchers, however, Venus's atmosphere is simply too dry: It doesn't contain enough water for there have been oceans that slowly evaporated as the planet warmed.

The two pervading theories for Venus' history include the planet having always been as hot as it is today, meaning that water never existed in liquid form on its surface, or alternatively, Venus having slowly heated up due to the greenhouse effect over many years, evaporating any water away. "Both of those theories are based on climate models, but we wanted to take a different approach based on observations of Venus' current atmospheric chemistry," study co-author Tereza Constantinou, a PhD student at Cambridge's Institute of Astronomy, said in a statement. The researchers describe in the paper how they calculated the rate of destruction of water, carbon dioxide and carbonyl sulphide in the atmosphere of Venus. These gases must be replenished by gases released from volcanism in order to keep the atmospheric composition stable. Therefore, the gases released by volcanoes on Venus are 6 percent water at most, unlike on Earth, where volcanic outgassing is mostly water vapor. This implies that the magma within Venus' volcanoes is also low in water content. "To keep the Venusian atmosphere stable, then any chemicals being removed from the atmosphere should also be getting restored to it, since the planet's interior and exterior are in constant chemical communication with one another," Constantinou said. Previous research has also found that unlike Mars and Earth, which have clear signs of past erosion by liquid water, Venus's surface has no evidence of landscape carving. Life as we know it requires liquid water to survive, which is why its presence is used by astronomers as a yardstick for the potential existence of extraterrestrial life. "We won't know for sure whether Venus can or did support life until we send probes at the end of this decade," said Constantinou. "But given it likely never had oceans, it is hard to imagine Venus ever having supported Earth-like life, which requires liquid water." Several spacecraft have successfully landed on the surface of Venus, but only a handful survived more than a few minutes due to the planet's extreme conditions. The Soviet Union's Venera spacecraft were the only probes to transmit data from the surface. Venus is technically in our star's Goldilocks Zone, which is the range of distances from a star where conditions might be "just right" for liquid water to exist on the surface of a planet. Therefore, the discovery that Venus may never have had liquid water at all has implications for the search for potential extraterrestrial life out in the cosmos. "Even though it's the closest planet to us, Venus is important for exoplanet science, because it gives us a unique opportunity to explore a planet that evolved very differently to ours, right at the edge of the habitable zone," said Constantinou. We will hopefully be able to find out more about Venus' history when NASA's DAVINCI mission arrives at the end of the decade. "If Venus was habitable in the past, it would mean other planets we have already found might also be habitable," said Constantinou. "Instruments like the James Webb Space Telescope are best at studying the atmospheres of planets close to their host star, like Venus. But if Venus was never habitable, then it makes Venus-like planets elsewhere less likely candidates for habitable conditions or life. "We would have loved to find that Venus was once a planet much closer to our own, so it's kind of sad in a way to find out that it wasn't, but ultimately it's more useful to focus the search on planets that are mostly likely to be able to support life—at least life as we know it." Do you have a tip on a science story that Newsweek should be covering? Do you have a question about Venus? Let us know via science@newsweek.com.

References

Constantinou, T., Shorttle, O., & Rimmer, P. B. (2024). A dry Venusian interior constrained by atmospheric chemistry. Nature. https://doi.org/10.1038/s41550-024-02414-5