The clouds of Venus join the shortlist for potential signs of life in our solar system

This image of Venus was created using data that NASA's Mariner 10 spacecraft collected on Feb. 7 and 8, 1974, shortly after the spacecraft's closest approach to Venus on Feb. 5.
This image of Venus was created using data that NASA's Mariner 10 spacecraft collected on Feb. 7 and 8, 1974, shortly after the spacecraft's closest approach to Venus on Feb. 5. (Image credit: NASA/JPL-Caltech)

Venus isn't the only world beyond Earth where scientists have gotten a possible whiff of life.

Researchers announced today (Sept. 14) that they've spotted in Venus' air the fingerprint of phosphine, a stinky gas that here on Earth is produced only by microbes and humans, as far as we can tell. 

The new find is not a detection of alien life. But it does suggest that something intriguing and mysterious may be occurring in Venus' clouds, an environment that astrobiologists have flagged as potentially habitable for microbial life.

Related: Strange chemical Venus clouds defies explanation. A sign of life?
6 most likely places for alien life in the solar system

Intriguing and mysterious things are happening on other potentially life-supporting worlds as well. For example, NASA's Mars rover Curiosity has rolled through several plumes of methane inside the Red Planet's Gale Crater and determined that background concentrations of the gas vary on a seasonal basis.

This is potentially exciting stuff, given that the vast majority of the methane in Earth's atmosphere is generated by living organisms. In addition, ultraviolet radiation from the sun breaks methane down in Mars' air within a few hundred years, so the stuff Curiosity is sniffing must have been emitted relatively recently. 

But methane can be produced abiotically as well — for instance, by chemical reactions involving hot water and certain kinds of rock. And it's possible that the Gale Crater surges were caused by "burps" of methane that has been locked underground for millions or billions of years, scientists say. In short, Mars methane is far from a convincing biosignature at the moment; we don't know nearly enough to make such a monumental call.

There's also astrobiological action farther out in the solar system. Take the Saturn moon Enceladus, which harbors an ocean of liquid water beneath its icy shell. NASA's Cassini spacecraft identified complex organic compounds — the carbon-containing building blocks of life as we know it — in the plume of water vapor wafting from Enceladus' south polar region.

Organics are not proof of life by themselves. The molecules are widespread throughout the solar system; they've been found in meteorites and in the tails of comets. But Enceladus' plume is generated by geysers blasting material from the moon's subsurface sea into space. 

So, Cassini's observations show that potential chemical precursors to life — and perhaps even signs of life itself — are floating in this possibly habitable environment, which also likely features an energy source that organisms could tap into.

Cassini also spotted complex organics in the air of another Saturn satellite: Titan, the second-largest moon in the solar system. Scientists think Titan hosts two potentially life-supporting environments — a buried ocean of liquid water, and frigid surface seas of liquid methane and ethane. (If life does swim in Titan's hydrocarbon seas, it would be very different than that of Earth, which requires liquid water.)

These hints and clues may be building toward some very big discoveries in the not-too-distant future. NASA's recently launched Mars 2020 rover Perseverance, for example, will hunt for signs of ancient life after touching down inside the Red Planet's Jezero Crater in February 2021. Perseverance will also collect and cache several dozen samples that NASA and the European Space Agency will bring to Earth, possibly as early as 2031.

NASA is also developing a Titan mission called Dragonfly, which will land a rotorcraft on the big moon in 2034. Dragonfly will study Titan's complex chemistry, assess the moon's habitability and search for possible biosignatures, among other tasks.

We could see a Venus life hunt in the next few years as well. California-based company Rocket Lab aims to launch a private mission to Earth's hellishly hot sister planet in 2023. The plan involves dropping small, instrument-laden probes through the Venusian atmosphere to look for signs of life inthe planet's sulfuric-acid clouds.

So it's not crazy to think that we could soon get an answer to that biggest of queries: Are we alone?

"We're the first generation that could actually address this question, other than in a philosophical way," Seth Shostak, a senior astronomer at the SETI (Search for Extraterrestrial Intelligence) Institute in Mountain View, California, told "And that is special."

Mike Wall is the author of "Out There" (Grand Central Publishing, 2018; illustrated by Karl Tate), a book about the search for alien life. Follow him on Twitter @michaeldwall. Follow us on Twitter @Spacedotcom or Facebook.

Join our Space Forums to keep talking space on the latest missions, night sky and more! And if you have a news tip, correction or comment, let us know at:

Mike Wall
Senior Space Writer

Michael Wall is a Senior Space Writer with and joined the team in 2010. He primarily covers exoplanets, spaceflight and military space, but has been known to dabble in the space art beat. His book about the search for alien life, "Out There," was published on Nov. 13, 2018. Before becoming a science writer, Michael worked as a herpetologist and wildlife biologist. He has a Ph.D. in evolutionary biology from the University of Sydney, Australia, a bachelor's degree from the University of Arizona, and a graduate certificate in science writing from the University of California, Santa Cruz. To find out what his latest project is, you can follow Michael on Twitter.

  • rod
    "So it's not crazy to think that we could soon get an answer to that biggest of queries: Are we alone?"

    My observation. While the search for life in the universe continues, including here in our solar system, *verified* life is yet to be shown in science (other than on Earth). Wait and see. Yet if life can only be shown here on Earth, including a fossil record, the answer to the question is - we are it, at least for biological life :)
  • Ken Fabian
    The leap from "Phosphine on Earth comes from biological processes" to "Therefore Phosphine on Venus must come from biological processes" is a huge one and not well grounded. Far more likely IMO that there are unknown non-biological processes at work.
  • Carl Swart
    Ken Fabian said:
    The leap from "Phosphine on Earth comes from biological processes" to "Therefore Phosphine on Venus must come from biological processes" is a huge one and not well grounded. Far more likely IMO that there are unknown non-biological processes at work.

    Certainly agree with your point. In fact, it is too huge to deduce any such conclusions, in my view.

    Strangely, it's a hydride covalently bonded with a pnictogen (in this case, obviously, phosphorus). Rather nasty little chemical. Certainly in aerobic settings, so any adventurous would-be explorers might think twice if they want to take their chances with a particle, 20 parts per billion, that might spontaneously explode and would certainly inhibit breathing and which in Venus' atmosphere would probably be about the most hospitable substance there (not even to mention the ground, which is even less friendly).Colonization certainly seems far-fetched.

    And yet, still, that it is there. Phosphine would not last very long in the acidic soup that is Venus' sky. Sulfuric acid and sunlight--both fairly ample things, clearly, would not allow it to exist long at all. So for there to be a presence enough to detect, continuously, it must have some source.

    The amount the team has detected, though it seems small, is orders of magnitude more than conventional other sources could be leaving. I share your skepticism of jumping to "biological processes" (as I have no idea how... or more importantly where---anything biological might sustain itself in such a hostile environment. But that leaves us with: what process is causing it, and continuously?

    It is such a stumping question that, aside from the question of life on Venus, is an extraordinary discovery.
  • Wally Mayo
    I believe there may be a small chance that they will find the remains of microbial life 50–65 km above the surface of Venus, not because I believe there is a possibility of indigenous life in the upper atmosphere of Venus. You see, there is scientific evidence establishing that diatoms and other microorganisms are wafted up into Earth’s upper stratosphere and beyond 25–100 km above Earth’s surface. Geology 41, no. 11 (November 2013): 1187–90, doi:10.1130/G24829.1; Milton Wainwright et al., “Isolation of a Diatom Frustule Fragment from the Lower Stratosphere (22–27 Km)-Evidence for a Cosmic Origin,” Journal of Cosmology 2013, volume 22 (August 9, 2013): 10183–10188. ]From there, passing dust particles will transport a few of these microorganisms to the upper atmosphere of Venus. Another transport route would be large meteoroids bombarding Earth with sufficient force to export Earth rocks and soil into interplanetary space. For example, astronomers have calculated that meteoroids have deposited about 20,000 kg of Earth material on average on every 100 square km of the Moon’s surface.
    So, it is inevitable that the remains of Earth life have been transported to Venus’s upper atmosphere by natural means.
    Earth was hostile enough 3.83 billion years ago to, against incredible odds, to have life emerge. Elsewhere, we can just starting with habitable zones: water, UV, planetary electric field, planet rotation rate/tidal locking, planet rotation axis tilt, astrosphere stellar magnetic wind, then the galactic habitable zones inc. co-rotation zone (just inside of), far from super novae, staying near plane of rotation, far from any large galaxy, and much more. The math is insanely against it.
    So, sorry, just color me as a skeptic.
  • Carl Swart
    Wally, respectfully they considered the possibility. It nowhere near explains the amount of PH3 discovered. I believe you are right about the probability, but unless there is something missing here, earthborne traces are not the cause (they have found ~10*8 times as much!)

    Data Figure:
    Full narrative:
  • jpdemers
    Admin said:
    Venus isn't the only world beyond Earth where scientists have gotten a possible whiff of life.

    The astronomers who did the measurements are just as skeptical as any of us are - they explicitly say that it's the result of a previously unknown process, which could be organic or inorganic. The latter, of course, is far more likely.
    Given the critical role of metalloenzymes in life as we know it - even in the simplest forms of life - I find it especially hard to imagine life in the clouds, where metals are surely scarce.
  • stevelee
    `Well, as it turns out, the air in Venus suggests that it could be somewhat hospitable. Read up and discuss over at this thread. `

    No it doesn't.... it suggests that there was once life there.
    I wonder if Mars and Venus had evolved life at the same time.
    I'm fairly certain venus can't support it above ground anymore. No matter what gases you find.
    We all want to find the kinda life we can relate to, the visible, breeding kind.
    something that isn't simply a tree, or a planet.
    But getting all excited and expecting actual living organisms.. I'd say the Galilean moons are a better bet.
    Or, as i've been saying for decades.. goto mars and dig very deep.
  • OliverClosehuf
    As an average nobody, I'm not worried about the question "are we alone?". Someone has to be first and there is no evidence an average schmo like me can access that would prove that isn't us.

    I'm more concerned with how we can terraform Venus and get some use out of it before the Sun grows too hot for mankind to make use of it. If there is something already living there, well , should have evolved faster.

    There's got to be some kind of baking soda asteroids out there we can strap an engine on and slam them into Venus to help neutralize the acidic atmosphere. Send some bacteria that eats acid and poops oxygen. Maybe people wanting to test their solar sails could park several in orbit around Venus and create a constant eclipse, help cool things down. It's a big lab we can practice climate control on and end up with prime real estate :-), Well, our great great great great....... great grand kids anyway.
  • RamanarayananSp
    For life to be in space, to sustain it Life force to be present. One of the main reason for Earth to have life is its position with respect to Sun.

    Also the thinking facility is very essential for Life. Each organ in our body functions because of its latent Intelligence.

    The observation reveals that looking from Earth the Sun and our Moon appear almost the same Angular size.

    The reason for this is the ratio of the distance from Earth to the diameter of the object (Sun and Moon respectively) is almost 107 to 110.

    Our search in the Space for this unique coincidence can be a factor to determine life in a planet.

    This may be a wild guess based on observation and perspective...
  • Kamal Ibrahim
    Assuming there is a kind of life on Venus in such harsh environment, could mean that the environment was once within the perfect levels for some kind of microbial life . Then it shifted to a more severe environment in a long slow process that might had enabled some of the microorganisms to gradually adapt to the new extreme environment.