Venus as seen by NASA’s Mariner 10.
Credit: NASA/JPL-Caltech
Although the Venus we know today is unfathomably hot and toxic, some researchers have long suspected that Earth’s neighboring “twin” was once capable of supporting life. As the theory goes, Venus was previously cooler and covered with liquid oceans, making it potentially hospitable to any Earth-like life forms that may have formed or arrived there. But new research out of England has rung the death knell for that particular hope. An analysis of Venus’s atmospheric makeup reveals that the planet has always been devoid of liquid water, making it inhabitable—at least to the type of life we understand.
Questions about Venus’s potentially hospitable past began to arise in the mid-1900s, when Heinz Haber, Carl Sagan, Harold Morowitz, and other scientific heavyweights began to focus on the planet’s early atmospheric and surface conditions. They thought that before Venus’s thick atmosphere produced the runaway greenhouse effect that makes it so brutally hot, the planet’s climate was much like Earth’s. Its temperatures could have been cool enough to support life, but warm enough to maintain vast bodies of liquid water.
To see whether Venus could have once been friendly to life, Tereza Constantinou, a PhD student at the University of Cambridge, led an analysis of the planet’s current atmosphere. In order to have produced the liquid oceans necessary to support Earth-like life, Venus’s sea of magma—which the planet possessed at the beginning of its existence—would have had to cool quickly, allowing water to condense. If this had happened, water would have become trapped in the crystallized magma and stored within the planet’s interior. What’s stored within a planet is ejected when its volcanoes erupt, which means Venus’s volcanic explosions would have spewed water into its atmosphere.
The volcano Idunn Mons on Venus.
Credit: NASA/JPL-Caltech/ESA
Constantinou and her professors used existing atmospheric composition data to see if they could reverse-engineer a planet that once held water oceans. Instead, they found that the planet’s volcanic eruptions were “dry,” or lacking in water. This means Venus’s magma likely cooled slowly, producing steam instead of liquid water and preventing Venus from trapping water within its interior.
This isn’t the first time humans have been disappointed by Venus’s inability to host Earth-like life. When NASA’s Mariner 2 spacecraft swung by Venus in 1962, it recorded temperatures ranging from 300 to 400 degrees Fahrenheit, as well as 20 times the atmospheric pressure found on Earth. Many people grieved the loss of the admittedly romantic yet widespread dream of finding extraterrestrial life on Venus. But Sagan, still an assistant professor at Harvard, took the opportunity to make a point that could still stand today.
“It is more likely that if there is life on Venus, it is probably of a type that we could not now imagine,” Sagan said in the 1963 NASA film The Clouds of Venus.
Though some scientists’ Venus dreams appear to have been dashed yet again, Constantinou made the same point this week that Sagan made more than 60 years ago. “This doesn’t completely rule out any life,” she told The Guardian. “It rules out Earth-like life.”