With a surface hot enough to melt lead and with clouds of sulphuric acid above it, it is a planet often called Earth’s “evil twin” – similar in size, yet worlds apart.
Some scientists have long believed it was once much more hospitable, home to cooler temperatures and oceans of liquid water. But now researchers have dealt a blow to the idea that Venus ever hosted life as we know it.
Scientists say an analysis of the planet’s atmosphere has revealed the interior of Venus is dry, suggesting it has never had the oceans of liquid water traditionally thought necessary for life to begin.
“This doesn’t completely rule out any life. It rules out Earth-like life,” said Tereza Constantinou, first author of the research from the University of Cambridge.
The question of whether Venus has ever been habitable – and might yet host life in its acidic clouds – has long been a hot topic among scientists. Some believe the planet was once much more like Earth but then underwent a runaway greenhouse effect. Others believe Venus has always been inhospitable.
Constantinou noted that early in the formation of Venus, the planet was covered in a vast sea of magma. If this cooled quickly, water would have condensed and formed water oceans. However, this process would also have trapped water in the magma as it crystallised, meaning the interior of the planet would be water-rich. As a result, water would be ejected when volcanoes erupt.
“If you look at any photos of volcanism on Earth, you see kind of these large billowing clouds coming out. Most of that is water,” she said.
But if the magma cooled slowly, water would have ended up as steam in the atmosphere. Crucially, in this scenario, water would not be trapped inside the interior of the planet.
Writing in the journal Nature Astronomy, Constantinou and colleagues report how they studied the chemistry of the planet’s atmosphere to shed light on the water content of its interior.
The team said the unchanging nature of Venus’s atmosphere meant the rate at which substances were lost must equal the rate at which they were replaced, with the latter driven by volcanic activity.
However, when the team analysed the ratios of substances being replenished in the Venusian atmosphere, they found very little water was being added; in other words, volcanic eruptions were “dry”.
“The scarcity of water in volcanic emissions reflects an equally dry Venusian interior,” said Constantinou.
The team said the findings were not consistent with Venus having had surface oceans of water in its past, and hence a climate traditionally considered habitable.
The team’s conclusion could soon be tested: later this decade, Nasa is due to launch the DaVinci mission to carry out flybys of Venus and drop a probe to its surface.
Constantinou said resolving the question could help astronomers narrow down their search for habitable planets beyond our solar system. “[Earth and Venus] provide this natural laboratory really close to us for studying how habitability, or the lack of it, evolves,” she said.
