Did Venus Once Host Oceans? Scientists Provide Answers

WASHINGTON—Earth is a world dominated by oceans, with water encompassing approximately 71 percent of its surface. Venus, our nearest neighbor in the solar system, is often referred to as Earth’s twin due to their comparable size and rocky structure. Despite its current barren and scorched landscape, could Venus have once been a planet adorned with oceans?

The answer is no, based on recent research that analyzed the water content within the planet’s interior—a crucial factor for determining if Venus ever had oceans—by examining its atmospheric chemical makeup. The study established that Venus has a notably dry interior, aligning with the theory that the planet became arid after an early period in its history when its surface was dominated by molten rock—magma—and has since remained desolate.

Water is deemed a vital element for sustaining life, thus suggesting that Venus was never capable of harboring life forms. Furthermore, these findings do not bolster a previous theory that Venus might possess a hidden reservoir of water beneath its surface, remnants of a former ocean.

Volcanic activity serves as a means of uncovering insights into the interiors of rocky planets by releasing gases into their atmospheres. As magma travels from a layer within the planet known as the mantle to the surface, it brings forth gases from deeper layers of the interior.

On Earth, volcanic gases are primarily composed of over 60 percent water vapor, indicating a water-rich interior. In contrast, researchers found that gases released during volcanic eruptions on Venus contain no more than 6 percent water vapor, a sign of a dehydrated interior.

“We propose that a habitable past would mean Venus’ present interior is rich in water, whereas a dry history would correlate with a dry present-day interior,” stated Tereza Constantinou, a PhD student at the University of Cambridge’s Institute of Astronomy and the lead author of the study published on Monday in the journal Nature Astronomy.

“The chemical composition of the atmosphere indicates that volcanic activity on Venus emits very little water, suggesting that the planet’s interior—the source of such volcanism—is equally parched. This aligns with the notion that Venus has had a consistently dry surface and has never supported life,” Constantinou further explained.

Venus is the second planet from the sun, with Earth being the third.

“Two distinct narratives regarding water on Venus have been proposed: one suggesting that Venus enjoyed a temperate climate with liquid surface water for billions of years, and the other positing that an early hot Venus never formed surface water,” Constantinou elaborated.

With a diameter of approximately 7,500 miles, Venus is slightly smaller than Earth, which measures about 7,900 miles across.

“Venus and Earth are often referred to as sister planets due to their similarities in mass, size, density, and proximity to the sun. Yet, their evolutionary trajectories have diverged significantly,” Constantinou stated.

“Currently, Venus exhibits extreme surface conditions compared to Earth, characterized by an atmospheric pressure 90 times that of our planet, surface temperatures reaching around 465°C (869°F), and a corrosive atmosphere filled with sulfuric acid clouds. These stark differences present unique challenges in understanding Venus as more than just Earth’s counterpart,” Constantinou remarked.

The narrative has been quite different for Mars, the fourth planet from the sun.

Evidence from its surface indicates Mars once harbored an ocean of liquid water billions of years ago, a feature absent on Venus. Research published in August, leveraging seismic data collected by NASA’s InSight lander, suggests that Mars may store a significant amount of liquid water deep within its crust, enough to cover its entire surface if brought to the surface.

Although Venus has been less extensively studied than Mars, new exploration endeavors are on the horizon. NASA plans to launch the DAVINCI mission in the 2030s, which will investigate Venus from its clouds to its surface via both flybys and a descent probe. Similarly, the European Space Agency’s EnVision mission is scheduled to perform radar mapping and atmospheric analysis in the same decade.

“Venus serves as a natural laboratory for exploring how habitability—or the absence thereof—develops over time,” concluded Constantinou.

By Will Dunham