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Oxygen Discovery Could Complicate Search for Alien Life

Scientists did not expect to find molecular oxygen at Comet 67P/Churyumov-Gerasimenko.
Scientists did not expect to find molecular oxygen at Comet 67P/Churyumov-Gerasimenko.

The strange, duck-shaped comet that ESA’s Rosetta spacecraft has been orbiting for more than a year just got a bit stranger: Like plants on Earth, the comet is blowing molecular oxygen, O2, into the space around it. Molecular oxygen is thought to be rare in the cosmos – or at least exceptionally tricky to detect.

“It is the most surprising discovery we have made so far,” says Rosetta team member Kathrin Altwegg of the University of Bern. The team first spotted the oxygen about a year ago and took its time ruling out sources other than the comet itself. “The first time we saw it,” Altwegg says, “I think we all went a little bit into denial because it is not expected to be found in a comet.”

Of course, molecular oxygen is common on Earth, having first been pumped out in enormous quantities by photosynthetic blue-green algae about 2.5 billion years ago. Until now, though, astronomers have only spotted gaseous O2 in a handful of other places, including two distant molecular clouds. The new observations, reported today in Nature, not only force a reconsideration of the very early solar system, they also throw a bit of a curveball at scientists hoping to identify the signatures of life on other worlds.

“The finding is definitely a wake up call for exoplanets and the search for life,” says Sara Seager of MIT. “O2 is the most prominent gas on our biosignature gas list.”

Back to the Beginning

Comets are icy, space-traveling time capsules. Unlike planets, where internal ovens have more or less cooked and rearranged the planet’s ingredients, a comet’s original building blocks are preserved. So, scientists can use the icy dirtballs to peer back in time, all the way to the beginning of the solar system when small bits of frozen debris were colliding and forming comets. As the thinking goes, the molecules trapped in a comet reflect the composition of the dusty primordial nebula that swirled around the very young sun.

Out there, far beyond the orbit of Neptune, temperatures were obviously quite cold. But until now, no one thought it was cold enough or placid enough for two oxygen atoms to meet, link up, and stay together.

“All the models say it shouldn’t be there,” says study author Andre Bieler of the University of Michigan in Ann Arbor.

And while molecular oxygen only accounts for a small percentage of the total amount of stuff escaping from the comet – about 3.8 percent, relative to water – finding it at 67P is still enough to make scientists reconsider the composition and temperature of that primordial dust cloud. “This ice hasn’t been heated up enough to be reprocessed,” Bieler says.

Gassy molecular oxygen has only been observed around two other stars, suggesting that it’s a rare component of the interstellar medium. Perhaps, scientists now say, that result reflects the difficulty of detecting O2 remotely.

“When we find new molecules in comets, they’ve nearly always been found in the interstellar medium,”says Mike A’hearn of the University of Maryland, College Park. But, he adds, “the abundance [in 67P] is low enough that it’s unlikely we would have ever seen it in remote sensing.”

O2 and the Search for Little Green Microbes

Here’s what the problem could be for scientists hunting for the signatures of life on exoplanets: No one thinks there are exhaling microbes on 67P. Yet molecular oxygen, as Seager says, is at the top of the list of gases that could indicate the presence of extraterrestrial life. And if it is naturally common in the cosmos, then O2 might need to be reconsidered as a potential biosignature.

On the other hand, high levels of O2 in a planet’s atmosphere could still reflect the presence of life.

“The O2 lifetime is so short in atmospheres it won’t be present for long unless it is continually produced,” Seager says, noting that there are many ways to produce molecular oxygen that don’t necessarily involve life. “The comet shows us there are situations we hadn’t considered, and this will happen over and over again.”

35 thoughts on “Oxygen Discovery Could Complicate Search for Alien Life

  1. It goes to show all of us (the layman) that we know very little about the Universe. It seems to be that before we attempt to go to Mars, that we should do more studies about what’s beyond our planet and that can be shared with ALL of us on earth so that we all learn at the same pace.

    1. Going to Mars *is* a way to study what’s beyond our planet. A scientist in the field for a few days is worth a 100 robotic missions, with respect to science returned. Not sure what you’re implying about us all learning at the same pace. Do you mean we should all have PhDs so that we learn what scientists are doing. Makes no sense.

    1. I, for one, appreciate your empirically simple/eloquent statement which does, in every sense, stay on subject, that is, “To know, we as a collective &, hopefully, collaborative community should realize we really don’t know. And in this ‘WAY’, may the magic of belief and believing become open paths, not only to new roads, but, check-it-out, to new maps?!?” Heck, I’m not one to normally get on a soap box, but I really do appreciate the sentiment I interpret through your words, because as I’ve perused latter posts, from others, on this subject, I have been overcome with sadness and dismay due to adversity & conflict which emanate from such extreme superfluous base lines of thought such as syntax, perceived gender trait(s) of contributing scientists, and misperception of previous theoretical statement as common-majority-accepted-proven-fact. Now come-on naysayers, give at least some quarter to those of whom are exploring new frontiers and then having to come back to US and communicate their findings. Not only are they sharing new and unstudied data, they are sharing discovery which challenges our very construct of reality. I think I can speak for Mohammad.S.Qurashi and myself when I say, “Relax a bit and enjoy the ride. Please, do not get caught-up in the chaotic muck and myer of judicial factual accountability. These concepts are way to much in flux, and to get our itty-bitty-brains around the infinitely vast probability of possibility; we are going to have to let-go-and-let-it-all-hang-loose!

  2. Ms. Drake,
    “Icy dirt balls”? I’ve looked at photos of the comet and I see little or no ice. While I do see dirt, I also see solid rock. What process is it that turns “small bit of frozen debris” into solid rock? Or into the shape of the comet, complete with voids? That theory is hard to swallow given the photographic evidence. Surely there are better theories that would support the visual evidence?

    1. Everybody can read in Wikipedia that comets are popularly described as “dirty snowballs”. I guess that scientists from ESA planned Philae spacecraft landing on comet 67P/Churyumov–Gerasimenko based on that assumption. The landing failed. Philae’s harpoon anchors couldn’t secure and stabilize the lander on the surface of the comet. The comet surface was a rock as you pointed out, not dirty snow. Philae bounced twice and ended in partial shade. If scientists responsible for 1 bln euro project made such mistake – why do you expect Ms. Drake to be correct?

      ND: Hi, Jozef. One quick thing: Please try and be respectful in your comments — to me, to the scientists, and to other commenters. Now, regarding “icy dirtball”: Wikipedia might call comets “dirty snowballs,” but Wikipedia isn’t necessarily the most accurate resource out there. It’s a good start, but the scientific literature is a much richer place to search. There has, in fact, been a debate among scientists for a little while (check out this paper from 1989) about whether “dirty snowball” or “icy dirtball” is a more accurate term. Recent observations from Comet 9P/Tempel 1, as well as 67P, suggest that comets might contain more dust than ice — making “icy dirtball” a more accurate description. That’s not the entire reason I used that term, though. I try and avoid cliches and overused descriptions, and “dirty snowball” falls into both of those categories.

      1. Hi Nadia (ND), I did not mean disrespect to you or other commenters. Scientific literature suggests that there is a difference between women and men – how they express their opinions. Women are more sensitive to social factors, men are more straightforward. I am sorry that I do not have a habit to respect people who attach a label “scientist” to themselves and I do not believe in everything what they say or write.

        I respect people like C Gould who think logically and who point discrepancies between facts like photos and cliche phrases repeated after “scientific” articles. I pointed in my comment that people labeling themselves as “scientists” who believe in cliches like “icy dirtball” can cause multi-million failures when a spacecraft tries to land on rock, not dirty snow or dirty ice.

        1. Jozef, the reason the lander ‘bounced’ as has been described is that 1- the comet had so little gravity and 2- the surface of the comet is made up mostly of dust and the harpoon used had nothing to stick to. If the comet had been rocky the harpoon would have stuck to the surface and the lander would not have bounced

          1. Harald, Philae tried to take dirt samples from the comet surface. Unfortunately its drill broke and samples were not taken. Rock was too hard. If the comet surface was dust then Philae landing and sample taking would be successful.

        2. Jozef, I would love to read the scientific literature you referenced about the differences between women and men. Care to site it? Any sound argument, scientific or otherwise, will be explicit about its sources (as ND was kind enough to do in her response). Otherwise, how can we assess their quality or be sure these sources even exist?

    2. perhaps what their detection devices can see far outweighs what you see in a black and white pic. perhaps you arent looking at rock but dirty ice????

    3. What colour is dirty ice that has got space dust stuck all over it? …a dirty rocky colour…?
      Also, some parts of comets are bits of rock that it has collected.

    4. Check out the Electric Universe Theory. They have been following this story for several years, and their predictions have generally been borne out.

  3. I’m not sure if it just the picture of the comet . I’m looking at but it looks to be a chiseling . Of maybe a solider and they left the metal or metallic looking tool in the neck of the art work.

  4. A couple of basic questions:

    (a) Is the idea that the comet trapped O2 from the gaseous disk of the early system and that this O2 is now being slowly released ?
    (b) Couldn’t the O2 have formed from atomic oxygen within the comet itself (possibly because surface substrates are available within the comet).

  5. That comet is just saying “Wait …Wait look at me, look at me. I’m life. I live I breath, I feel now that you know it”

    I guess the presence of oxygen isn’t the catch all signs of life:)

  6. Good article, ND. I guess the question I always have is why anyone would expect to find life exactly as we know it elsewhere in the universe. I think that the wondrous variety we see on our own planet is likely a microcosm of the vastly diverse possibilities in the universe. If scientists only look for what we know life is on this planet, they may miss the clues that would identify a larger picture of the composition of life in the universe. Anything that makes them rethink is a good thing.

  7. It just goes to show that models of what should be and shouldn’t be that scientists use and calculations on computers are utter rubbish. The cosmos is and will always have mysteries. Science thinks it knows it all, yet as far as I know they still don’t know lots about our own planets mysteries let alone the universe / multiverse.

    Our little brains will never understand the cosmos.

    1. Robert, no one who self-identifies as a scientist could possibly carry on as if she or he “knows it all”. Engineers might think like that (as they apply principles and understandings that Scientists generate.) Science is about discovering, exploring and documenting phenomena that were Unknown. Then science encompasses acquired knowledge based on data amassed through rigorous experimental procedures. Discoveries are reported as strictly delimited aspects of phenomena in specific areas, and are expressed as mathematical models. Those models become bases for theorems that stand to be proven wrong. Science is tentative! (These notions are covered in Chapter 1 of “Freshman Science 101”). The scientific process is an ever-evolving representation reality, Scentists state their arguments precisely. They do not throw words and opinions around as blog commenters commonly do with complete freedom. Scientists who make unwarranted claims, don’t show proofs, don’t submit their findings to skeptical scrutiny? They get kicked out of the scientific community and stripped of their Scientist badges.

      How could one call oneself an “explorer” of something that is already well known? Here’s a quote from Stephen Hawking, possibly the greatest scientist of our time (certainly among the most famous):
      “Some people will be very disappointed if there is not an ultimate theory. I used to belong to that camp, but I have changed my mind. I’m now glad that our search for understanding will never come to an end, and that we will always have the challenge of new discovery.”
      — Stephen Hawking (courtesy of M. Goldstein’s Physics Foibles)

      Of course there are individuals in every walk of life (including Scientists) who are insufferanly egotistical and condescending.!And ignorant of truths and realities outside their areas of interest,

  8. I do not think that O2 presence is connected with life. Obviously people and animals need oxygen to breath. But presence of oxygen in any form does not suggest life presence. Oxygen is the third most abundant element in the Universe. Atomic oxygen is very reactive, as the single atoms of oxygen tend to quickly bond with nearby molecules; on Earth’s surface it does not exist naturally for very long, though in outer space, the presence of plenty of ultraviolet radiation results in a low Earth orbit atmosphere in which 96% of the oxygen occurs in atomic form. Therefore atomic oxygen inside a comet quickly reacts forming O2. When comet travels closer to the Sun and it is heated to higher temperatures and releases gases including oxygen than after some time ultraviolet radiation splits O2 into O.

    1. Jozef, dioxygen (or O2) is produced by photosynthetic processes in living organisms, and is therefore connected to life in the form in which it appears on earth. What you meant to say is that dioxygen does not by itself provide sufficient evidence for life. Because something does not constitute sufficient evidence, however, does not eliminate it as evidence. An exoplanet hosting photosynthetic organisms would be expected to have an atmosphere with a higher percentage of dioxygen than a planet without any photosynthetic organisms, all other things being equal.

  9. There is a tendency (and an erroneous one in my view) to see comets and meteors as ‘primordial’, or as somehow neutral chunks of everyday matter strewn randomly in space waiting for the day they collide with or become entangled with other such objects.

    To my mind, these objects are chunks of a much larger earler mass (moon or planet) which was obliterated by a large collission in the early era of the solar system. There is absolutely no reason to believe that other planets and moons existed in orbit around the Sun long before the present solar system settled. So it;s very likely that another planet(s) held other O2 producing life forms or conditions which were then obliterated by collisions, sending these chunks of debris into orbit and are now visible as meteors, comets and the oort cloud.

    Our solar system may well be a second, third or fourth-generation solar system awaiting the next upheaval that could re-arrange the present settled situation and send chunks of rock with ant, cow and human genes flying around the cosmos!

  10. This is not a new story for Buddhists. This all has been said by Lord Buddha in his teachings & sermons. As per Buddhism there are thousands of millions of galaxies, planets & living beings in those planets. There’s nothing special about that. Let them live without disturbance. If we awaken unknown planets results may be disastrous.

  11. If microbial life is ubiquitous on 67P, 67P could have its own Gaia principle in which 4% oxygen is the current steady disequilibrium. It is much harder to explain the constant 4% disequilibrium without life than with life. If not life, what is keeping the atmospheric O2 percentage constant, despite the continual temperature and solar radiation changes the comet has been experiencing?

    In fact, James Lovelock suggested long ago that the atmospheric conditions that persist on 67P could be explained only by a terrestrial biota.


    Here is the money quote, in terms of scientists’ ignoring the glaring evidence right before their eyes:

    “As far as we knew the combination of methane and O2 was a hint that you had life, but on our comet we have both methane and O2, but we don’t have life, so it is probably not a very good bio-signature” Altwegg said.

    Talk about simply presupposing away the most reasonable explanation with a wave of one’s hand!

    Alternative #1:

    What all planetary scientists used to consider a clear bio-signature (because it is) is no longer a bio-signature at all. Oxygen and methane can and do persist in a “stable” atmospheric disequilibria indefinitely through some bizarre, unknown, and previously unimagined primordial chemical processes! All of our most prominent solar system formation models need to be rethought, and we need to devise a previously unimagined and currently unknown process for how “primordial” O2 ice somehow managed to get evenly distributed within 67P billions of years ago. We also need to explain how this previously unimagined O2 ice somehow managed to persist undisturbed for billions of years, despite its incredibly reactive nature. Finally, we need to show how such primordial O2 managed to be distributed in such a way to result in constant replenishment to maintain 67P’s stable atmospheric disequilibria, even as its distance from the sun keeps changing.

    Alternative #2:

    We could just consider the possibility that 67P does indeed have all the previously agreed upon biosignatures of life, and when microbial life infects a comet, it terraforms the comet to achieve a stable atmospheric disequilibria, just as it has on Earth.

    Only consensus bias against microbial life existing on comets makes the first alternative more “scientifically conservative” than the second. Both alternatives completely annihilate the current consensus paradigm.

  12. “. . . astronomers have only spotted gaseous O2 . . .”? Really? “only spotted”? As opposed to what? “only dotted”? And “. . . only accounts for a small percentage . . .”? And “. . . Gassy molecular oxygen has only been observed around two other stars . . .”? Writer is moving the “only” farther and farther away from its home. Hmm. In NATIONAL GEOGRAPHIC, no less. Surely a proofreader can protect the writer from embarrassment over such silly writing where clear thinking is so important.

  13. Interesting article, shows us how little we still know, how much we may still have to adjust our models.

    But in relation to the various comments: some appear to be showing genuine interest, but unfortunately, some others just show how they want to impose their own models (expressed as factual knowledge) on the rest of us. This irritates me.

  14. As Kelly Duke suggests, perhaps the correct explanation is the first one that pops to mind–maybe there is photosynthetic life on this comet. Why not?

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