Millions of space geeks happily responded Monday to a study that showed that the atmosphere in Venus contains phosphine, a chemical byproduct of biological life. But no one would have been more excited or less surprised by the discovery than the late, great Carl Sagan – who said that this day might come more than 50 years ago.
Now best remembered as the presenter of the most watched PBS series ever Cosmos, the author of the book behind the film Contactand the guy who put gold discs of earth music on NASA’s Voyager missions, Sagan actually began studying our two closest planets. He became an astronomer after being inspired as a child by Edgar Rice Burroughs̵
But as Cosmos fans know, Sagan’s star-studded sci-fi hopes never beat his hard-edged science. He shot down an early “proof” of life on Mars. He predicted that the surface of Venus would become insanely hot, even before NASA’s first Venus probe in 1962, which he was working on, confirmed it. And he was the first scientist to see the hellish landscape of Venus as a result of a runaway greenhouse effect – one he knew could show the way to Earth’s climate-changing future.
So it was so much more surprising when Sagan was the co-author of a paper that suggested that we could still one day find a microbial life above our sister planet. “If small amounts of minerals are stirred up to the clouds from the surface, it is in no way difficult to imagine an original biology in the clouds of Venus,” he wrote in Nature in 1967 – two years before NASA landed on the moon. “While the surface of Venus makes the hypothesis of life unlikely, Venus’s clouds are completely different.”
As Sagan pointed out, a high carbon dioxide atmosphere was no obstacle. Up on the 50 km long layer, at the top of Venus’ clouds, the conditions are actually hospitable and almost earth-like. Organisms could thrive in the upper range in the same way that bacteria thrive around overheated, CO2-rich ventilation ducts at Yellowstone. Add sunlight and water vapor to CO2, he said, and you have the recipe for the building blocks of life, photosynthesis.
“Sagan’s work with Venus was formative, though few today remember his influence,” said Darby Dyar, president of NASA’s Venus Exploration Advisory Group. “His idea was prior and still makes sense today: between the hellish surface conditions of today’s Venus and the nearest vacuum in outer space must be a temperate realm where life can live on.”
Just 11 years after Sagan made his prediction, another Venus probe discovered methane in the atmosphere – which could be considered a prediction for the presence of organic matter. Scientists like Sagan were wary of the discovery; no one could prove that methane meant life beyond a reasonable doubt. (We also found it on Mars in 2018 and have not yet explained it). Yet no one ever gave a reasonable alternative to why the methane might be hanging around Venus.
Sagan died in 1996 amid a criminally long dry spell for NASA’s Venus exploration. But his idea lived on. In 2013, we discovered large amounts of microbes in the clouds above the ground. More than 300 varieties to the surprise of the scientist who collects them – microbes are actually less close to lower altitudes. In 2016, NASA models showed that Venus once had oceans for at least 2 billion years. It backed up a theory by planetary expert David Grinspoon, which suggests that microbial life migrated to the clouds when conditions became too harsh for life on the surface a billion years ago.
Call them the original climate refugees.
Science did not stop, even when we only used terrestrial telescopes to do so. We have found evidence of active volcanoes on the surface that would “stir minerals” into the atmosphere, just as Sagan suggested. In 2018, another study of the Venus atmosphere revealed mysterious “dark spots” that scientists speculated could be signs of microbial life – large amounts of it. How much? We need more research to find out. “I came to this paper out of frustration,” co-author Sanjay Limaye told me last year. “We have not been looking for organisms [on Venus]. Why not?”
Why not? As I wrote earlier this year, Venus was unfairly shifted aside for Mars in NASA’s budget priorities. Although Venus is denser and more Earth-like, Mars had a surface we could stand on, which was easier to sell for our 20th-century “space colonization” mindset.
But the more we look at Venus, the more we have to reconsider what exploration looks like.
Quietly, inside and outside NASA, a “Venus community” grew that wanted to explore its clouds and began begging for budget remnants. Its most exciting moment so far came in 2015, when NASA unveiled a concept mission called HAVOC – a Zeppelin, basically that you did not need to fill with helium or hydrogen. Just ordinary old earth air floats on top of Venus’ dense atmosphere. Tear the balloon fabric and the high pressure could actually keep the air from escaping weeks.
As you might expect, the Venus community was in full swing with excitement over the phosphine discovery on Monday. Not least because the NASA administrator had just tweeted the magic words: time to prioritize Venus.
Life on Venus? The discovery of phosphine, a by-product of anaerobic biology, is the most significant development ever in the construction of the matter of life from earth. About 10 years ago, NASA discovered microbial life at 120,000 feet in the Earth’s upper atmosphere. It’s time to prioritize Venus. https://t.co/hm8TOEQ9es
– Jim Bridenstine (@JimBridenstine) September 14, 2020
There is, of course, caution in spades. Phosphine is also found in the large, fighting gas giants Jupiter and Saturn. But to explain why it would be present on a rock as small as Venus if it were not for life, scientists say you will have to propose a geological process that we do not yet know about.
“The intriguing discovery of phosphine in the atmosphere of Venus just reinforces the growing body of evidence that Venus is a probable, perhaps the most likely, other place in our solar system where life may have existed now or in the past,” says NASA’s Dyar. “Venus holds the keys to our understanding of the evolution of rocky planets as home for life.
“This discovery may be the first of many to come as NASA and other countries renew a Venus exploration program.”
Currently, ESA, the Russian Space Agency and NASA have all Venus probe plans in place that could arrive in this decade; the phosphine announcement could very well move launch dates up. If and when the next probes find more evidence of life over the solar system’s most mysterious planet, we are one step closer to confirming Carl Sagan’s legacy as a visionary Venutian genius.