A group of astronomers has discovered that Venus has never been capable of supporting life, putting to rest long-held theories suggesting that our nearest planetary neighbor may have once resembled Earth more closely.
A group of astronomers has discovered that Venus has never been capable of supporting life, putting to rest long-held theories suggesting that our nearest planetary neighbor may have once resembled Earth more closely.
Researchers from the University of Cambridge investigated the chemical makeup of Venus’s atmosphere. They concluded that the planet’s interior is currently too dry to have ever contained enough water for oceans to form on its surface. Hence, Venus has likely been an extremely hot and inhospitable world throughout its entire history.
The findings, published in the journal Nature Astronomy, have significant implications for understanding what makes Earth unique, as well as for the quest to find life on planets beyond our Solar System. While many exoplanets share characteristics with Venus, this study indicates that astronomers should concentrate their efforts on worlds that are more akin to Earth.
From afar, Venus and Earth appear to be almost twin-like: they are similar in size and both are rocky planets. However, up close, Venus resembles a hostile counterpart, enveloped in thick clouds of sulfuric acid, with surface temperatures averaging around 500°C.
Despite these harsh conditions, astronomers have for years been exploring the possibility that Venus might have once had liquid oceans capable of supporting life, or that some undiscovered form of ‘aerial’ life currently thrives in its dense clouds.
“We won’t know for certain whether Venus can or did support life until we send probes later this decade,” said the study’s lead author, Tereza Constantinou, a PhD student at Cambridge’s Institute of Astronomy. “But since it likely never had oceans, it’s hard to envision Venus ever supporting life as we know it, which depends on liquid water.”
When looking for life elsewhere in our galaxy, astronomers typically target planets situated in the habitable zone around their stars, where temperatures would allow for the existence of liquid water on the surface. Venus serves as a crucial benchmark for defining where this habitable zone exists around a star.
“Even though it’s the closest planet to us, Venus plays a key role in the study of exoplanets because it offers a unique chance to examine a planet that developed in a fundamentally different way from ours, right at the edge of the habitable zone,” Constantinou remarked.
There are two main theories regarding how conditions on Venus may have changed since its formation 4.6 billion years ago. The first suggests that Venus once had a temperate environment that could support liquid water, but a runaway greenhouse effect, fueled by extensive volcanic activity, caused the planet to overheat. The second theory posits that Venus originated as a hot planet, never allowing liquid water to condense on its surface.
“Both theories are rooted in climate models, but we aimed to take a fresh approach by analyzing observations of Venus’s present atmospheric chemistry,” explained Constantinou. “To maintain a stable atmosphere on Venus, any chemicals lost must also be replenished, as the planet’s interior and exterior are in constant chemical exchange.”
The team assessed the current rate at which water, carbon dioxide, and carbonyl sulfide molecules are being destroyed in Venus’s atmosphere—these must be replenished by volcanic gases to keep the atmosphere balanced.
Volcanism provides insights into the interiors of rocky planets like Venus by releasing gases from deeper layers as magma travels from the mantle to the surface.
On Earth, volcanic eruptions primarily release steam, owing to our planet’s water-rich interior. In contrast, analysis of the volcanic gases expected to sustain Venus’s atmosphere revealed that water constitutes at most six percent of those gases. These arid eruptions indicate that Venus’s interior, which generates the magma and volcanic gases, is also lacking in water.
By the end of this decade, NASA’s DAVINCI mission is set to further investigate whether Venus has always been a dry and unwelcoming planet through a series of flybys and a probe intended for the surface. The outcomes could refine astronomers’ search for potentially habitable planets orbiting stars in the galaxy.
“If Venus was indeed habitable in its past, it would suggest that some of the planets we’ve discovered might also have the potential for habitability,” said Constantinou. “Instruments like the James Webb Space Telescope excel at studying the atmospheres of planets close to their stars, such as Venus. However, if Venus proved to be uninhabitable, it would reduce the likelihood that Venus-like planets elsewhere are suitable for life.”
“While we would have been thrilled to discover that Venus was once similar to Earth, it’s somewhat disappointing to learn it wasn’t. However, it ultimately directs our efforts toward planets that are more likely to support life as we understand it.”
The study received partial funding from the Science and Technology Facilities Council (STFC), which is part of UK Research and Innovation (UKRI).
