Everyone Is Searching for Life on Mars. Why They Should Be Looking on Venus Instead

Venus is hell. But life may exist there, researchers say

An ultraviolet image of Venus, with a colorful band around its south polar vortex.
An ultraviolet image of Venus, with a colorful band around its south polar vortex. Credit: JAXA / ISAS / DARTS / Damia Bouic
Oded Carmeli
Oded Carmeli
Oded Carmeli
Oded Carmeli

“In the summer of 2016, I went on a scientific expedition in the Ladakh region in northern India,” recalls Sanjay Limaye, a senior planetary scientist at the University of Wisconsin-Madison. “Many Israelis travel in Ladakh, a very high region in the foothills of the Himalayas. My purpose was to examine whether there is life in the acidic springs there – but all the springs we examined turned out to be completely nonacidic. In short, it wasn’t a very exciting trip for me. On the last day, however, we arrived at the salt lake of Tso Kar, not far from the capital, Leh, at an elevation of perhaps 5,000 meters above sea level.

“While we were walking along the shore, I noticed the powdery remnants of desulfurizing bacteria on the leaf of a weed,” said Limaye, in a recent phone conversation with Haaretz. “Suddenly a gust of wind simply carried the powder – together with the bacteria, of course – into the air. For me it was a eureka moment. I remember thinking: Could something like this happen on Venus, too? Is it possible that life existed and developed on Venus, and afterward wandered into the clouds and stayed there?”

When we think of extraterrestrial life in our own solar system, most of us think of Mars. More serious geeks have their eye on the subterranean oceans on the ice moons of Jupiter’s Europa, or Enceladus of Saturn. True fantasists may even hope to find methane-based life in the lakes of the latter planet’s largest moon, Titan. Venus, however, is probably the last place we think of in this context. David Bowie doesn’t have a song about life on Venus and Elon Musk has no ambitions to found a city of a million people there. But while the good people on Earth are focused on Mars, mysterious particles are cruising among the clouds of Venus. At times, they multiply and densify into huge symmetrical strips that cast their shadow across half the planet, reacting to and even altering their surroundings. And Sanjay Limaye and others think these particles could be alive.

For years, Venus, planet of love and beauty, was considered Earth’s “twin sister.” Second closest to the sun and the planet nearest to Earth, it also most closely resembles our world in size, mass, composition and distance from the sun – a distance that makes possible the existence of liquid water on the surface. On paper, at least, Venus sounds like a terrific destination for space tourism, settlement and the search for life. In fact, people used to dream of Venus as a world filled with rain forests, jungles, swamps – all inhabited by exotic alien beings.

Venus may be dotted with Pompeiis, and we have no way to know about them. Fossils or cities would be concealed under a layer of lava and buried under a toxic layer of clouds.

Those dreams were shattered once and for all on October 18, 1967, when the Soviet spacecraft Venera 4 became the first human-made object to rip through Venus’ cloud blanket. The Soviets knew that Venus is hotter than Earth – in 1964, Mariner 2 accurately measured Venus’ surface temperature and told us it was inhospitable. They also knew that the atmosphere there is far denser, because through the telescope Venus looks like a sealed, static sphere. It’s always cloudy on Venus. The skies never clear up.

Accordingly, before its mission, Venera 4 was tested in extreme conditions, until its engineers were certain it would withstand the pressure and the heat. Then the probe entered Venus and opened its parachutes. At 52 kilometers above the surface, Venera 4 measured an atmospheric pressure similar to that of Earth and a temperature of 33 degrees Celsius – like summertime in Tel Aviv. Twenty-six kilometers later, the pressure had soared to 22 Earth atmospheres and the temperature to 263 degrees. The spacecraft went up in flames.

The Soviets did not despair, however, continuing their efforts throughout the next 18 years. They built an armored Venera 5, more durable than its predecessor. That didn’t help; it melted at 320 degrees. Venera 6 was even better armored, and for safety’s sake it entered Venus from its dark side, like a thief in the night. It too was burned alive.

Venera 7 was fortified like a tank. It looked more like a poyke pot than a spacecraft. And it succeeded in landing on the planet and dispatching signals for 23 minutes. Venera 8 survived for 50 minutes. It didn’t have a camera, but it was able to prove that visibility on Venus resembles that on Earth on a cloudy day – leading its engineers to conclude that it was worthwhile to send a camera. Venera 9 entered Venus encased in a special pressure chamber, insulated and cooled, which protected the lander long enough – 53 minutes – for it to send the first photograph ever from the surface of another world. The blurred black-and-white image looks like an engraving from an antique edition of Dante’s “Inferno.” Venera 10 lasted 65 minutes; Venera 11 functioned for 95 minutes and took a lightning bolt; Venera 12, 110 minutes. Venera 13 still holds the world record: 127 minutes on Venus and the first – and last – color photos of the surface. And that’s it. Since 1985, no spacecraft has landed on Venus. No country has even dared to try.

Images of the surface of Venus, taken by the Soviet spacecraft Venera 13 in 1982. The data the brave Venera probes sent horrified the denizens of Earth: Venus is hell. USSR Academy of Sciences/Brown University
Images of the surface of Venus, taken by the Soviet spacecraft Venera 13 in 1982. Credit: USSR Academy of Sciences/Brown University

The data the brave Venera probes managed to send horrified the denizens of Earth: Venus is not a twin sister – it’s hell. The planet that is closest to and most resembles our own is also the hottest planet in the solar system – far hotter than Mercury, the closest to the sun. The temperature on Venus is 462 degrees Celsius, hot enough to melt lead. And that’s not an average: Day or night, summer or winter, at its north pole or the equator, the temperature on Venus is almost always 462 degrees.

Besides the weather, there is the air. The atmospheric pressure on Venus is 91 times that of Earth; standing on its surface would be as bone-crushing as diving one kilometer into the depths of the sea. It also has occasional sulfuric acid rain. Not to worry, however: That precipitation, too, evaporates before reaching the surface.

Welcome to hell

How did Venus get to be such a terrible place? In two words (and three atoms): carbon dioxide. In contrast to the thin air that we breathe, comprised of 78 percent nitrogen, 21 percent oxygen and only 0.04 percent carbon dioxide – on Venus that primary greenhouse gas constitutes 96 percent of the atmosphere. Both planets have a similar quantity of carbon dioxide, but on Earth most of it is trapped in subterranean silicate rocks, whereas on Venus most of it was released into the atmosphere and caused a chain reaction known as the “runaway greenhouse effect”: First, carbon dioxide is released from the ground, traps the planet’s thermal emissions and heats up the world. The high temperature vaporizes some of the bodies of water on the surface, such that the water vapor, also a greenhouse gas, rises into the atmosphere, which again raises the temperature. In the third, and final, stage, all the oceans begin to boil and their vapors escape into space after being broken down by the extra heat into hydrogen and oxygen. The process of plate tectonics, which spreads at the ocean floor, stops for good, so there is no possibility of rocks that could reabsorb the carbon dioxide being exposed.

And yes, that is exactly what happens when we burn such fossil fuels as petroleum and coal, and emit carbon dioxide. Just to be clear, Earth is absolutely not expected to turn into Venus anytime soon, but the average temperature on our planet has already risen by one full degree since the Industrial Revolution, and is expected to rise by another two degrees by the end of the century. Anyone who still doubts that the release of carbon dioxide from the bowels of the earth heats planets, is invited to visit Venus and see for himself. In fact, that experiment has already been conducted, and the results are unequivocal.

But Venus was not always a hothouse. “Earth and Venus may have started their lives, about 4.5 billion years ago, with similar atmospheres – carbon dioxide and water vapor,” says physicist Michael Way, of NASA’s Goddard Institute for Space Studies, at Columbia University in New York. “In the 100 million years that followed, Earth absorbed the carbon dioxide in the soil, the temperature dropped and the water vapor thickened into rain clouds, which filled the oceans. We have evidence that a similar process occurred on primeval Venus. The interesting question is how long Venus succeeded in preserving its water before it dried up. Was it long enough for life to develop?”

In September, Dr. Way stunned participants in the annual European Planetary Science Congress, in Geneva. Venus, he declared, might have been a blue planet for three billion years – more than enough time to allow life as we know it to develop. In fact, Venus could have been a warm and watery world to this day, were it not for an event, or a series of events, that released vast quantities of carbon dioxide from the ground 715 million years ago – a mere twinkling of time in cosmic terms.

Basing themselves on the proportion of deuterium (an isotope of hydrogen) to hydrogen in Venus’ atmosphere, Way and his colleagues calculated that water once covered most of the planet, at depths varying from four meters to 525 meters. Using Rocke-3D, the Goddard Center’s advanced climate simulation program, they ran five computerized models that hypothesized different levels of oceans covering the planet. In all five scenarios, the scientists found that Venus was capable of maintaining stable temperatures of between 20 and 50 degrees Celsius for billions of years, and could even have preceded Earth as the first habitable planet.

Venus’ cloud layer possesses all the conditions needed for life: energy from the sun, water vapor, and such nutrients as carbon, phosphorous, sulfur, chloride, oxygen.

“It is quite possible that Venus maintained the conditions for life before Earth did,” Way notes, in a conversation with Haaretz. “The first geological period in the history of our planet is called ‘Hadean’ – after the [Greek] god of the underworld, Hades – but today we entertain the opposite hypothesis: that primeval Earth was able to cool down very fast, and we don’t find life there during its first billion years precisely because it was frozen. In all the advanced models, scientists find it difficult to postulate a hot Earth during the genesis of our solar system, when the intensity of the sun was three-quarters of what it is now. My idea was that with Venus there was no need to consider that primeval cold period, because the planet is closer to the sun. No special atmospheric conditions are needed to sustain a warm environment. Take Earth’s atmosphere today, place it on Venus 4.2 billion years ago, even 4.3 billion, and you’ll get marvelous weather.”

So what happened to the once-tropical planet? Way and his colleagues hypothesize that an apocalyptic volcanic eruption occurred 700 million years ago, melting the rocks on Venus and freeing the gas stored in them. It wasn’t so much a volcano as bursts of lava from huge cracks in the land and oceans that created what’s known as a “large igneous province.” For example, a similar super-eruption created the Siberian Traps region in Russia, and is responsible for the Permian-Triassic extinction 252 million years ago – the deadliest extinction in Earth’s history.

The difference is that Venus never recovered from that massive eruption. Carbon dioxide covered the sky, while the magma (the molten or semi-molten material from which igneous rocks are formed) hardened and covered the surface, which did not allow the rocks to reabsorb the greenhouse gas. The evidence for this theory? Venus is literally covered in it. In contrast to the wizened face of Earth, the moon or Mars, 85 percent of Venus’ surface is perfectly smooth, unscarred by craters.

According to Michael Way, of NASA, “Extensive basalt-leveling events dissolve the silicate rocks and release vast quantities of carbon dioxide into the atmosphere. We see events like this in Earth’s history, in which the average temperature rose by five to 10 degrees. Now imagine three successive eruptions like that, and you’ll get a rise of 20, 30 or 40 degrees. The results will be grave. Earth was pummeled like that, but with gaps of hundreds of millions of years, and was able to recover. Venus seems to have simply been unlucky. It took one especially powerful blow 700 million years ago, or a few blows in succession, and it never got up again.”

A computerized visualization of land-ocean patterns on Venus.
A computerized visualization of land-ocean patterns on Venus. Credit: NASA

That idea is no less than stunning. If life did exist on Venus, it enjoyed an evolutionary grace period of billions of years. Compared to the evolutionary time axis of our world – that’s enough time to divide, multiply, breathe oxygen, proliferate cells and create complex, spectacular organisms, whose images would be preserved in fossils. And if life on Venus emerged before life on Earth, or faster, it is possible that even real civilizations of beings were horrified by the sight of their planet’s surface being overturned. Venus may be dotted with Pompeiis, and we have no way to know about their existence. Fossils or cities – all would be concealed under a layer of lava, which is buried below a thick, seething, toxic layer of clouds.

“It’s possible that there were complex forms of life on Venus and we will never know about it,” Way says. “Well, I need to be careful with the word ‘never.’ Certainly not in my lifetime or in my children’s lifetime. NASA has a program called HOTTech for developing electronic systems that can withstand high temperatures, but it’s still in its fledgling state. A great many years will go by before we are able to send rovers that will excavate sedimentary rocks and look for fossils on Venus, like we’re doing on Mars.”

The color of Venus

If all this sounds totally fantastical, well, we haven’t yet come to the true anomaly: color. Even though Venus is the brightest object in our night skies (apart from the moon, of course), amateur astronomers like me generally don’t bother aiming their telescopes at the planet. The so-called Morning Star (or Evening Star, depending on the season) is a boring, monotonous yellowish-white. Yet, a world possessing such a dense atmosphere should reflect the sun’s light across all wavelengths. Venus should not be yellowish-white: It should simply be white.

Why, then, doesn’t Venus seem to have the right color? As far back as the early 20th century, astronomers used ground-based telescopes to photograph Venus in the ultraviolet – meaning those wavelengths of electromagnetic radiation too short to be visible to the human eye – and discovered tiny particles scattered across the entire spectrum and absorbing most of the ultraviolet light and blue color visible to the eye. In the professional jargon, which comes up with words even when there’s nothing to say, these particles are called “unknown absorbers.” Furthermore, instead of being well-mixed, these absorbers form symmetrical atmospheric waves known as “dark patches.”

'Is it possible that life existed and developed on Venus, and afterward wandered into the clouds and stayed there?'

Of course, not everything that is unidentified is alive. Concluding that they are alien beings should be the last resort, once all the physical and chemical possibilities have been exhausted. Indeed, for a century, scientists have been talking about inorganic alternatives such as allotropes of sulfur or molecules of iron chloride, yet no known material has been found that absorbs electromagnetic radiation exactly as Venus’ absorbing particles do. The fact is, all matter absorbs light and refracts light in a slightly different way, and the light-absorbing particles detected in the clouds of Venus act in a way that recalls above all the microorganisms that live in Earth’s clouds. They are even the same size.

“Almost every cloud on Earth contains bacteria,” explains Sanjay Limaye, who in 2018 co-authored an article in the periodical Astrobiology about “Venus’ Spectral Signatures and the Potential for Life in the Clouds.” He adds, “Some bacteria remain in the air for a long time, others are washed away quite quickly by rain. We have to understand that Venus’ cloud layer possesses all the conditions needed for life: energy from the sun, water vapor, and such nutrients as carbon, phosphorous, sulfur, chloride, oxygen. It all exists, but in meager supply. The beauty of our hypothesis is that the colonies arise only when the environment has sufficient humidity and nutrients. When the stock is depleted, the bacteria disappear. What can we compare this to? The blooming of algae in the oceans.”

That idea itself isn’t new. In 1963, astronomer Carl Sagan suggested that colonies of bacteria are responsible for the absorption we see of UV and visible light in Venus’ atmosphere. In 1967, he and the biophysicist Harold Morowitz published an article in the periodical Nature titled, “Life in the Clouds of Venus?”. “While the surface conditions of Venus make the hypothesis of life there implausible, the clouds of Venus are a different story altogether,” the two wrote, adding, “water, carbon dioxide and sunlight – the prerequisites for photosynthesis – are plentiful in the vicinity of the clouds.”

The innovation in this realm lies in the research of a postdoctoral researcher at the Technical University of Berlin, Yeon Joo Lee. She and colleagues, among them Limaye, compared images of Venus taken by the Japanese space probe Akatsuki, which has been orbiting the planet since 2015, with archival images from the European Space Agency’s Venus Express exploration mission, NASA’s Messenger spacecraft and the Hubble Space Telescope.

Lee’s research shows that between 2006 and 2017, the albedo of Venus – that is, the sunlight reflected back from the planet – diminished by half before returning to its regular level of illumination. The dramatic plunge in albedo was seen at exactly the wavelengths that are absorbed by the unknown absorbers. So it seems that it doubled itself and then was sliced in half within a decade.

“The unknown absorbers successfully control the reflectivity of light in short waves,” Lee explains. “The darkening of these wavelengths signifies multiplication of the absorbers. Planets don’t just dim by half within a decade, and it was hard to persuade colleagues about the decadal changes in the Venus albedo. Many people, including Sanjay [Limaye], suspected that the changes were due to instrumental aging, but not the nature of Venus. That is also the major reason why I compared the four different instruments.”

“Yeon Joo’s study is critical,” Limaye says. “She succeeded in persuading me that even if we take into account the sun’s natural cyclicality, Venus dimmed significantly – and significantly more than Earth. And in the same way that the blooming of microalgae influences the albedo here, bacterial growth in the clouds of Venus might be the reason for the dimming and brightening. In the case of Venus, the thickness of the clouds causes the albedo to be very high in the majority of the wavelengths. Venus cannot become brighter, but it can definitely become darker with the addition of dark matter.

“What is that dark matter?” he continues. “Well, it’s not distributed equally, although it is scattered across the whole atmosphere. On the illuminated side it also organizes in patches, in dark strips, and it’s clear that it reacts in some way to the sun’s cyclicality – but we aren’t able to say whether it’s a chemical reaction or a biological one. We aren’t able to say if it’s life.”

An ultraviolet image of Venus. Researchers suggest the dark parts are bacteria floating in the clouds.
An ultraviolet image of Venus. Researchers suggest the dark parts are bacteria floating in the clouds.

Chemical or biological, the result was dramatic: The weather on Venus changed.

Lee: “This is the first time someone has shown that the climate on Venus is changing in the present, too. The changes in ultraviolet absorption are extreme enough to affect the whole of climate’s dynamics, from the temperature to the wind velocity – a longtime scientific mystery in its own right. At the edge of the Venus cloud layer, the winds blow at dizzying speeds. When the absorbers multiplied, between 2007 and 2012, the wind velocity increased from 80 to 90 meters a second to 110 meters a second.”

Are we then witnessing microscopic life that is able to adapt its environment to its needs? “If it is life,” Way says, “then it looks as though it did a good job adapting to its harsh environment. On Earth, life fills every ecological niche, but it had billions of years of evolution to learn how to fill them. If life on Venus had a similar span of time to fill all the niches there, then yes, it’s possible that forms of life developed especially to survive in extreme environments such as clouds.”

But there is another possibility. The truth is that the clouds of Venus are the only place in the solar system where we human beings could hang out without a spacesuit – assuming there are comfortable temperatures of 30 degrees, gravity almost identical to that on Earth and protection against the sun’s dangerous radiation. Humans would still need an oxygen tank, of course, but bacteria don’t need oxygen. Indeed, there are bacteria on Earth that could live very pleasurably on the clouds of Venus. And maybe that’s exactly what they’re doing.

“We know for certain about intensive exchanges of rocks between planets,” Way notes. “We find meteorites from Mars on Earth, and we believe that there are meteorites that originated on Earth on Mars. We have found meteorites from Earth on the moon and from the moon on Earth. There is no reason to suppose that there are no meteorites from Earth and from Mars on the surface of Venus. There are microorganisms that could survive that journey and inseminate the atmosphere of Venus. Maybe we will look for life on Venus and find ourselves again.”

Generally, there’s something terribly frustrating in writing about the possibility of life on Venus. After all, if there is life or the vestige of life on Mars, it’s hiding under some rock. We can’t see it. But there are pictures of mysterious particles in Venus’ atmosphere that could be microscopic life. All that needs to be done to ascertain that is to dispatch a weather balloon to the dark patches to swallow up a few unknown absorbers, and determine whether they are biological or not.

But that is not going to happen anytime soon. No fewer than eight robots are today studying Mars – from the ground, from the air and from space – and they will be joined by four more in 2020. And Venus? There’s no mission there scheduled for the coming years.

When I speak with Limaye and Way, it turns out that they are both in Moscow for a workshop about Venera-D – a plan by the Russian Space Agency to launch a lander and orbiter to Venus. But the two scientists both make it clear that this is just talk.

“We are in the stage of disseminating ideas,” Way says. “In recent years NASA has shown little interest in Venus and the Russians have been unwilling to commit the necessary resources. Venus is still a world that is completely enveloped in mystery, where there is a great deal we don’t know. From the point of view of a scientist, this has an advantage and a disadvantage. The disadvantage: We have very little data that will limit our theories and models. The advantage: We have very little data that will limit our theories and models.”