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Rosetta’s Comet: Ingredients for Life

The thought that water and organic molecules might have arrived on the early Earth from the impacts of comets and asteroids has long been provocative, and our missions to nearby comets are now paying off with insights into the possibility. It was back in 2004 that the Stardust mission flew past Comet Wild 2, collecting dust samples that showed traces of the amino acid glycine. Possible contamination of the samples during their analysis left the question open, however.

Now we have news that the European Space Agency’s Rosetta mission has also found glycine — a significant organic compound that appears in proteins — at Comet 67P/Churyumov-Gerasimenko. The spacecraft’s ROSINA instrument (Rosetta Orbiter Spectrometer for Ion and Neutral Analysis) detected glycine in October of 2014, with later measurements taken during the August 2015 perihelion event, where cometary outgassing was at its peak.

Kathrin Altwegg (University of Bern), who led the study, calls this “…the first unambiguous detection of glycine in the thin atmosphere of a comet.” From the paper:

ROSINA’s double focusing mass spectrometer (DFMS) ionizes the incoming volatiles by electron impact ionization and detects the corresponding positively charged fragments. Unlike for meteorites or Stardust grains, there is no chemical sample preparation involved. Furthermore, the absence of a terrestrial source of glycine from the spacecraft is verified from observations before arrival at the comet. Therefore, glycine detected by DFMS has to be in this form already in the coma of the comet and is clearly not the result of contamination.

Although little glycine is released from the cometary surface, the detection of precursors to glycine formation, the organic molecules methylamine and ethylamine, is also significant. Glycine is the only amino acid known to be able to form without liquid water. Says Altwegg:

“We see a strong correlation of glycine to dust, suggesting that it is probably released from the grains’ icy mantles once they have warmed up in the coma, perhaps together with other volatiles. The simultaneous presence of methylamine and ethylamine, and the correlation between dust and glycine, also hints at how the glycine was formed.”

Grafikgross

Image (click to enlarge): An ESA infographic detailing the recent work on organic compounds found at Comet 67P/Churyumov-Gerasimenko.

We also get word, in the paper published by Science Advances, that Rosetta found phosphorus at Comet 67P/C-G. The researchers argue that the number of organic molecules ROSINA has detected at the comet, now including glycine and phosphorus, make a strong case for comets as a delivery mechanism for prebiotic chemistry. This marks the first time phosphorus, an ingredient in the framework of DNA and RNA, has been found at a comet.

The presence of glycine, phosphorus, and a multitude of organic molecules, including hydrogen sulfide (H2S) and hydrogen cyanide (HCN), seen in the coma of 67P/Churyumov-Gerasimenko supports the idea that comets delivered key molecules for prebiotic chemistry throughout the solar system and, in particular, to the early Earth, drastically increasing the concentration of life-related chemicals by impact on a closed water body. The simultaneous presence of methylamine and the correlation between dust and glycine also suggest that the pathways for glycine formation on dust grain ices, as described for the ISM or the protosolar nebula, could also account for the cometary glycine.

The paper is Altwegg et al., “Prebiotic chemicals – amino acid and phosphorus – in the coma of comet 67P/Churyumov-Gerasimenko,” Science Advances, 27 May 2016 (abstract / full text).

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Comments on this entry are closed.

  • Alex Tolley May 31, 2016, 10:09

    I don’t seem to be as excited as others over this discovery. Amino acids form quite easily, as the Miller-Urey experiment showed in teh last century, and those AAs included glycine (full list.

    Phosphorus is important for life, indeed is often the limiting factor for biomass, but again it is found on Earth and there is no reason to suspect that it wasn’t part of the primordial mix of elements ( abundance of elements).

    The issue for abiogenesis is much more complex that whether some raw ingredients for proteins are available. We are still arguing over the metabolism vs replication model coming first, and how any of that works, although RNA world that partially straddles both is a popular theory with much to commend it. But we haven’t yet found the bases for RNA (A,C,G,U) or DNA (A,C,G,T) in space, although A & G have been found in meteorites and believed not be be due to contamination. Recently chemists have shown how the nucleic acids could have been produced on Earth with chemistry. So how important is the finding of AAs on comets to the question of the origin of life?

    I’m optimistic that the ubiquity of the “building blocks” of life suggest that just possibly life is quite common on habitable worlds, even though we don’t yet know the details of abiogenesis. IOW, if there is any great filter, it is still in front of us, rather than behind us.

    • Curt Wohleber May 31, 2016, 15:53

      From a purely selfish perspective, I hope that the great filter is behind us.

    • Eniac June 1, 2016, 1:13

      I agree that there is a lot more to abiogenesis than presence of a few of the simplest organic molecules. I’d go further and claim that this not-quite-ubiquity of building blocks does NOT suggest a ubiquity of life. I also agree with Curt that that is probably a good thing, for us.

      • Alex Tolley June 1, 2016, 10:31

        At this point we cannot determine from first principles whether life is ubiquitous or rare in the universe. I have long been swayed by tangential arguments that Stuart Kauffman uses in his book (a tour de force?) >a href=”https://www.amazon.com/Origins-Order-Self-Organization-Selection-Evolution/dp/0195079515/ref=sr_1_1?ie=UTF8&qid=1464790272&sr=8-1&keywords=origins+of+order”>The Origins of Order: Self-Organization and Selection in Evolution. Most notably on self organization of metabolic processes. This book is based on a lot of computational work rather than hazy thinking, and remains one of my most important books in my library. It is the biology equivalent to Hofstadter’s famous Gödel, Escher, Bach: An Eternal Golden Braid on AI.

        While progress on abiogenesis seems slow, experiments keep pushing the chenistry of abiogenisis, most notably recently on RNA analogs and how they form under plausible conditions to start the RNA World. While it is possible these are all dead ends, at this point I am optimistic that we will be able to build plausible models for abiogenesis in the future, maybe even within what is left of my lifetime.

        Clearly a discovery of life elsewhere would be confirming evidence, and in this regards I am optimistic that telescopic observations will show evidence that biosignatures are present on suitable worlds in the HZ of other stars. A big win would be discovery of either microbial or fossil life in (not on) Mars, more remotely life in icy moon oceans, and possibly clues to prebiotic chemistry on Titan.

        Should life not be found on apparently suitable exoplanets, then I would go far as to say that we should go out and green the universe as a grand task for humanity for as long as we have that capability.We might even be able to start soon with advanced versions of StarShot carrying microbial life.

        • Eniac June 4, 2016, 11:59

          When (if ever) we do find plausible models that lead all the way from a plausible primordial lifeless environment to replicating RNA capable of sustaining evolution (i.e. a system where replication fidelity is sufficient for positive selection to not be overwhelmed by deterioration), then we’ll be a step closer towards actually estimating the chances of abiogenesis. My expectation is that those estimates will be very, very low (something like 10^-20, or even way much less), so all we would have done is confirm our initial suspicion. But who knows, you can dream….

          Also, consider that a really primitive replicating RNA system would be dependent on a very particular environment, one in which there is a large supply of free nucleotides and precise chemical conditions for replication. Such an environment would have to be stable for a very long time, until more complex metabolic pathways and cellular compartments could evolve to provide greater autonomy. This used to be called the Primordial Soup, a term which has fallen out of favor, unfortunately, for some reason. I am pretty sure that, in one form or another, there would have had to be such a soup, and that that in itself may contribute a very small factor to the abiogenesis equation.

          Too many people are misguided in thinking: “It did happen, so it cannot be that unlikely”. That thinking is misguided because it ignores the fact that life is necessary for us to be here to think about it. That produces a statistical observation bias that pins the chance of abiogenesis on Earth at 1, exactly, and makes it impossible to infer anything at all about the unbiased probability. It is this unbiased probability that would tell us how many other planets may be out there with life, and the answer could very well be none.

    • Eniac June 1, 2016, 1:20

      And I agree that finding them in space is mildly interesting, but totally irrelevant to how life formed on Earth. The primeval Earth with water, CO2, heat, lightening, minerals, etc surely is a much more likely source of organic chemicals than any space environment could be.

  • DJ Kaplan May 31, 2016, 12:30

    I’m excited, but yes, I guardedly agree with Alex that we have yet to see life arise spontaneously from the raw ingredients.

  • Michael June 1, 2016, 2:57

    Yes, Yes there is complex organic molecules there but there is something much more than that -materials for colony and world ships.

  • Mark Zambelli June 1, 2016, 6:32

    I agree with Alex …
    “I’m optimistic that the ubiquity of the “building blocks” of life suggest that just possibly life is quite common on habitable worlds, even though we don’t yet know the details of abiogenesis”

  • Ron S June 1, 2016, 15:37

    That amino acids and other compounds which life (as we know it) uses can be found here and there in the universe can be entirely unrelated to life and abiogenesis. The assumption is that abiogenesis is dependent on that source of those compounds. They can just as easily be parallel and unrelated processes. That is, the still unknown process(es) of abiogenesis may use either a different pool of these compounds, if the dependence is even valid, or synthesize these and other necessary compounds.

    What I take from these types of observations is that if these compounds are prerequisites for abiogenesis it is good to know that they can become available, and even abundant, through fairly simple natural processes. But I do not assume a cause and effect relationship.

  • ljk August 25, 2016, 10:49

    Rosetta captures comet outburst, possibly due to a landslide

    25 August 2016

    In unprecedented observations made earlier this year, Rosetta unexpectedly captured a dramatic comet outburst that may have been triggered by a landslide.

    Nine of Rosetta’s instruments, including its cameras, dust collectors, and gas and plasma analysers, were monitoring the comet from about 35 km in a coordinated planned sequence when the outburst happened on 19 February.

    “Over the last year, Rosetta has shown that although activity can be prolonged, when it comes to outbursts, the timing is highly unpredictable, so catching an event like this was pure luck,” says Matt Taylor, ESA’s Rosetta project scientist.

    “By happy coincidence, we were pointing the majority of instruments at the comet at this time, and having these simultaneous measurements provides us with the most complete set of data on an outburst ever collected.”

    Full article here:

    http://www.esa.int/Our_Activities/Space_Science/Rosetta/Rosetta_captures_comet_outburst