Is There Life on Mars and Venus?

You may have heard that the scientific community is buzzing with excitement over the discovery of Gliese 581g, an Earth-sized planet circling the red dwarf star Gliese 581, 20 light-years from Earth in the constellation Libra. Five other planets orbiting this star were already known, but what’s exciting is that the new one is smack in the middle of the star’s habitable zone, making it the best candidate ever discovered for an extrasolar planet with liquid water. And where water flows, is it possible that life follows?

This finding is a major blow to the creationists who insist that Earth must be the only life-supporting planet that exists. As the scientists who discovered Gliese 581g pointed out, finding a habitable planet this easily means that we’ve either been incredibly lucky, or such planets are common.

But I wanted to turn my attention a little closer to home for the moment. You might think, given the effort scientists are putting into finding Earth-like planets beyond the solar system, that we’ve exhausted all possibilities for discovering alien life any closer to home. Surprisingly, not only is that far from the truth, we have evidence which could imply the existence of life dwelling on our very nearest planetary neighbors.

Take Venus. Despite being Earthlike in size and composition, Venus has a surface of crushing pressure and 900-degree temperatures, making it almost certain that no life could survive – on the surface. But the surface isn’t the only environment on the planet where life could conceivably exist. The planetary scientist David Grinspoon, in a daring feat of imagination, hypothesized that free-floating microbial life could exist in Venus’ atmosphere. In the upper reaches of the Venusian atmosphere, the temperature is a far more hospitable 80 degrees, with the same pressure as Earth, and some evidence even suggests the presence of water. It’s possible that life began on Venus’ surface billions of years ago, but as the steadily increasing greenhouse effect turned the surface into an inferno, it escaped into the atmosphere, drifting high above the killing heat.

And this hypothesis isn’t pure speculation. There’s some tantalizing evidence which could indicate the presence of life in Venus’ clouds.

The astrobiologists Dirk Schulze-Makuch and Louis Irwin pointed out that Venus’ atmosphere contains very little carbon monoxide. This is curious, because lightning and ultraviolet radiation should be producing this gas in large amounts. Even more suggestively, Venus’ atmosphere contains significant amounts of three other molecules – hydrogen sulfide, sulfur dioxide, and carbonyl sulfide – which, at least on Earth, are only produced by life or by volcanic activity. Venus does have active volcanoes, but not as many as Earth (since it has no plate tectonics), and it’s not certain whether it’s enough to account for the measured abundances. It’s possible that some as-yet-unknown chemical pathway is breaking down carbon monoxide and producing these other compounds. But it’s also possible that what we see in our spectroscopes is the metabolic signature of Venusian life, drifting in the planet’s clouds and thriving to such an extent as to alter the balance of its atmosphere.

Mars has been explored much more thoroughly than Venus, and it too has given evidence to tantalize us. The two Viking spacecraft which landed on Mars in the 1970s carried experiments designed to test for the presence of life. The most surprising of these was the so-called labeled release experiment, which added water and nutrients to a sample of Martian soil. The nutrients were “tagged” with radioactive carbon-14, and the assumption was that, if there were microbes in the soil, they would metabolize them and release radioactive carbon dioxide gas. And when the experiment was run, the carbon dioxide was indeed detected. Even more excitingly, when the experiment was repeated after heating the soil to sterilizing temperatures, no gas was detected – as if any microorganisms in the soil had been killed off.

However, Viking’s gas chromatograph found no evidence of organic compounds in the soil. That seemed to be the death knell for possible life – until, in 2008, NASA’s Phoenix lander discovered a compound called perchlorate in Martian soil. Perchlorate becomes a strong oxidizing agent when heated, as the gas chromatograph does, and some scientists feel that this would have rapidly broken down any organic molecules and would explain why they didn’t show up in the analysis. The evidence from the Viking experiments is still much-debated and ambiguous, but it certainly doesn’t rule out the possibility of life.

Also, like Venus, Mars has anomalous chemical compounds in its atmosphere: in this case methane, which was detected by the European Space Agency’s Mars Express spacecraft. This molecule would rapidly decompose under Martian conditions, so for it to exist there means that something must be continually replenishing it. As with the anomalous compounds on Venus, it could be released by volcanic activity – except that Mars has no known volcanism, and is believed to be geologically dead. It’s possible that the methane is being produced by a geologic process called serpentinization. But it’s also possible that Mars is home to methanogenic bacteria, producing the gas as a product of their metabolism. Most likely, Martian methanogens would live far below the surface, deep underground where it’s warmer and there may be liquid water – similar to archaea on Earth that live in similar conditions deep within the crust.

The idea of life existing on either or both of these planets shouldn’t be too surprising. Although Venus is a suffocating inferno and Mars a freezing dry desert, both planets had clement pasts with surfaces where liquid water flowed. Both these planets, during the formation of the solar system, presumably received organic molecules from the same source as Earth’s. Depending on your assumptions about how likely abiogenesis is, life could well have started on all three planets at about the same time. We won’t know for sure, of course, until we’ve had a more detailed look – but it’s worth remembering that even the nearest shores of our vast and awesome cosmos may yet contain marvels we haven’t dreamed of.

About Adam Lee

Adam Lee is an atheist writer and speaker living in New York City. His new novel, Broken Ring, is available in paperback and e-book. Read his full bio, or follow him on Twitter.

  • Katie M

    I still remember my reaction when I saw the news about Gliese 581g. I was literally on the brink of tears :)

    Have you seen the recent news about Titan? Scientists replicated its atmospheric conditions in a lab and discovered that the stuff of life was forming. Not only does this point to possible life on Titan, it also seems to suggest that life does not necessarily need liquid to form.

    I’m feeling rather optimistic about the existence of extraterrestrial life :)

  • Darth Cynic
  • Darth Cynic

    Oh dear, I appear to have made a pigs ear out of inserting those links. My apologies and please find them below for any who wish to paste them into their browser.

    The Gliese 581g story.

    http://news.sciencemag.org/sciencenow/2010/10/recently-discovered-habitable-world.html

    An article from Science Daily on Europa.

    http://www.sciencedaily.com/releases/2008/12/081212092056.htm

  • Monty

    I think it’s also worth remembering that there are something like 10^21 estimated planets in the universe. So even if the chance of any particular planet being habitable is one in a billion (it’s likely much higher), and the chance of the conditions being right for abiogenesis at some point in its history (because it only needs to happen once) is also one in a billion, then there are still about a thousand potential life-holding planets in the universe.

  • http://Daylightatheism.org J. James

    Europa is all the buzz among the more hard-core exobiologists. It is the most likely place besides Earth to support life. It seems very similar to the famous “black smokers”, so who knows what wonders it has to behold? Venus, though, just wow… I envision sky-bacteria and insects, being eaten by floating Hydrogen-filled jellyfish…

  • Jim Baerg

    J. James:
    Not necessarily hydrogen filled. A mix of nitrogen & oxygen will lift a balloon in a carbon dioxide atmosphere. So a photosynthesizing lifeform could store oxygen it generates along with nitrogen it extracts from the surrounding ‘air’ (a few % of venus’ atmosphere) to keep it aloft. Any life there would have to be able to thrive under conditions of high acidity though, venus’ clouds are made of sulfuric acid droplets.

  • http://kagerato.net kagerato

    While it would be intriguing to find some other form of simple life out there in the universe, especially to see how it differs fundamentally from life on Earth, I suspect that what most people are interested in is whether there is any other intelligent life. Thus far, the answer to that question has been a resounding no.

    Many hypotheses have been proposed to try to explain why there don’t appear to be any other intelligent lifeforms within range of radio contact. The most common is probably the argument from improbability. That is, suitable planets around suitable stars are relatively rare, and the likelihood of abiogenesis is itself quite small. After that, you have to take into account some kind of evolutionary process, which would not lead to intelligence if it would serve no useful survival purpose in the environment. Finally, you have to run on top of that the possibility of an intelligent civilization exhausting itself before reaching the technical capacity for radio communication.

    It’s also possible that other intelligent life exists, but it’s too distant to be reachable. This explanation only makes sense if our current understanding of physics is correct, and it is genuinely impossible to breach the light-speed barrier. In which case, the further you go out into the universe, the more difficult it is to distinguish a radio message from sheer random noise.

    I don’t count on discovering intelligent life at any time. People are fascinated by groundbreaking and bizarre ideas, no matter how implausible. It’s just part of our curiosity.

  • Alex Weaver

    How long do you suppose it’ll be before the birthers accuse Obama of having been born in Venus’ atmosphere, then?

    Despite being Earthlike in size and composition, Venus has a surface of crushing pressure and 900-degree temperatures, making it almost certain that no life could survive – on the surface.

    I’m not sure this is such an obstacle. The pressure could be an issue, but after all, life manages to survive in California… >.>

  • John Nernoff

    It’s fun speculating on the existence of “life” elsewhere than earth. Unfortunately the life that may be found would overwhelmingly be uninteresting. Why?

    Take the history of life on earth, it being 4.5 billion years old, life after 1 billion years appeared as extremely primitive forms (unicellular, bacteria-like, molds, fungi). It wasn’t until about a half billion years ago (Cambrian) that more complex creatures appeared. But hardly any with communicative intelligence.

    So taking earth as a model of what we might expect in the Goldilocks zone (assuming that zone being the only likely spot in which life can appear), intelligent life (crows, apes, humans, ?dolphins) appeared in only a tiny time and space frame. In the 13.7 billion year old, and vast, universe, encountering a random planet would likely yield up only the odd bacterium, fungus, jellyfish, etc. — utterly dumb creatures.

    Yes, it would be stunning to many theists that “God” would waste his vast alleged powers creating slime molds. But that’s what we’d likely run into. We would not be getting into profound conversations with them. And any organism smarter than us would see us for what we are (chimps with atomic weapons) and more likely than not transporting themselves away as fast as they could.

  • Katie M

    “Unfortunately the life that may be found would overwhelmingly be uninteresting.”

    The mere fact that it would be extraterrestrial would make it EXTREMELY interesting :)

  • javaman

    If we made contact with such sentient being elsewhere, do you think they would have “gods” on their planet also ? If yes ,it would fascinating to hear their “bible” stories. Or would this planet have no “gods” at all, a totally natural atheist planet with the concept of god as an unknown.

  • Ritchie

    Venus has a surface of crushing pressure and 900-degree temperatures, making it almost certain that no life could survive – on the surface… In the upper reaches of the Venusian atmosphere, the temperature is a far more hospitable 80 degrees, with the same pressure as Earth,

    Okay, sorry to be really thick, but what exactly is meant by ‘pressure’ here?

    Venus is (very) roughly the same size as Earth – or slightly smaller, so why would the surface have a different pressure? What causes it? And what would that mean, in practical terms – does whatever gives Venus’ atmosphere a greater pressure than Earth’s also mean it’s atmosphere is somehow denser? Making it harder for airbourne partiles/bacteria to sink to the surface?

  • Yahzi

    I’m afraid I have to agree with the party-poopers. The religious crowd has utterly ignored quasars, black holes, and galactic super-structures; why would they even notice alien slime-molds? I mean, they routinely dismiss dinosaurs. The discovery of non-intelligent alien life (and it will be non-intelligent as Nernoff explains) will have no impact at all on theology.

    For the rest of us, though, it will be terribly fascinating, and I am appropriately excited by this latest news.

  • Boudica

    Cool…will we have to develop a Star Trek-style prime directive to not interfere with the slime molds?

  • Jim Baerg

    Ritchie #12

    There is a lot more gas in Venus’ atmosphere so with almost as much gravity as Earth there is a lot more weight of gas over each unit area. See this for details.

  • Valhar2000

    It’s fun speculating on the existence of “life” elsewhere than earth. Unfortunately the life that may be found would overwhelmingly be uninteresting. Why?

    It might be uninteresting in the sense that even Michael Bay, with his enormous powers, would not be able to make a summer blockbuster out of it*, but for the scientific community it would be the finding of the millenium, at least. If would be life distinct in origin from the life that exists now on Earth (which is, as far as anyone can tell, descended from a single common ancestor), or it would be another descendant of our common ancestor found in another planet, which would be the find of the millenium in and of itself.

    Ask PZ Myers what he would think about finding life elsewhere (though not what he thinks that likelihood of that is), and you will see biological geekery in its purest form.

    * I am, of course, kidding: Michael Bay can add explosions and cheesy dialogue to anything: he’s just that good.

  • http://anexerciseinfutility.blogspot.com Tommykey

    The discovery of non-intelligent alien life (and it will be non-intelligent as Nernoff explains) will have no impact at all on theology.

    IIRC, a year or two ago some official of the Catholic Church said that if there are intelligent beings elsewhere in the universe, then Jesus died on the cross for their sins as well.

  • kennypo65

    There is also the possibility that there is intelligent life nearby(within the 100 light year range), but they are less technologically advanced than we are. They may not have invented radio yet.
    Even if there are more advanced aliens, and even if we one day discover them, the theists will simply modify their beliefs to accomodate them. This is the catch-22 of having beliefs that are not based in reality. One can simply expand the parameters of belief to include Hyper-intelligent squid people from a planet orbiting Vega.

  • Alex Weaver

    There is also the possibility that there is intelligent life nearby(within the 100 light year range), but they are less technologically advanced than we are. They may not have invented radio yet.

    There’s also the bias this comic parodies.

  • http://thesnideatheist.blogspot.com the snide atheist

    No doubt Jesus travelled to many planets during his gig as a hippy cult leader. Of course, there may be some slight differences, like walking on a sea of methane instead of water, but I’m sure aliens throughout the cosmos share the same important parts – like hating homosexuals.

  • Ritchie

    Thanks Jim.

  • http://www.superhappyjen.blogspot.com SuperHappyJen

    But I already knew that there was life on Mars, Santa Claus told me so:

    http://www.youtube.com/watch?v=RmlE7ONKRcQ

  • http://www.daylightatheism.org Ebonmuse

    I hadn’t heard that the data for Gliese 581g had been questioned. Thanks, Darth Cynic, for pointing out that link. Hopefully we’ll get a definitive answer to this question soon. But even if this particular exoplanet turns out to be a mirage, there are a lot more stars out there to look at!

  • Valhar2000

    There is also the possibility that there is intelligent life nearby(within the 100 light year range), but they are less technologically advanced than we are. They may not have invented radio yet.

    From what I understand, they would have to be far more technologically advanced than we are for us to be able to detect with out current technology. They would have to build specialized equipment, far in advanced of what we can do ourselves, and use it specifically to broadcast detectable signals.

    In other words, barring arguments from biologists about the unlikelihood of intelligence evolving, this is one of those cases where absence of evidence is not evidence of absence.

  • http://eternalbookshelf.wordpress.com Sharmin

    Science is so very fascinating. There’s a whole universe out there to explore and so much to learn about it. My Astronomy and Cosmology teacher had mentioned Gilese 581g and the controversy over it as well. Thanks for writing about this.

  • lpetrich

    Fortunately, Gliese 581 g orbits its primary each 36.6 days, meaning that it’ll make 10 orbits/year, plenty for good statistics. Whether its presence is statistically significant or not is another story.

    Gliese 581′s planets, like many other extrasolar ones, were observed by watching the recoil that they cause on their primary stars. This produces a line-of-sight velocity of about

    (m(planet)/m(star))*sqrt(G*m(star)/a(planet))*sin(inclination)

    So the smaller and farther a planet is, the harder it is to detect with this technique.

    But we are getting to a point where we may be able to detect Earth-sized planets before long. If there are big planets, there have to be small planets, but can we see them?

  • Jim Baerg

    BTW there is a good discussion (mostly in the comments) about what conditions could be like on Gleise 581g or other tide locked planets at http://www.rocketpunk-manifesto.com/2010/10/goldilocks-planet.html