Image credit: NASA/FQTQ

Yesterday, scientists made an announcement that is, arguably, one of the most important assertions in the history of science: We have uncovered unequivocal evidence of alien life.  Yes, you read that correctly. Unequivocal evidence of alien life. No doubts.

These claims come from astronomer and astrobiologist Chandra Wickramasinghe, who is, among other things, Director of the Buckingham Centre for Astrobiology at the University of Buckingham. Last week, Wickramasinghe and colleague Dr. Max Wallis, from the University of Cardiff, claimed that icy features seen by the Philae lander on comet 67P/Churyumov–Gerasimenko are decisive signs of alien life.

Wickramasinghe outlined his assertions at the National Astronomy Meeting, “What we’re saying is that data coming from the comet seems to unequivocally, in my opinion, point to micro-organisms being involved in the formation of the icy structures." He continued to point towards evidence for alien life in a later conversation with From Quarks to Quasars, "I think the evidence for biology on comet 67P is very strong, even though they are indirect...I think that microbial life exists in abundance throughout the galaxy–most of the 100 billion or so comets in our solar system will be full of microorganisms. Comets brought life to Earth 4 billion years ago, and continues to do so even today."

So to sum, Wickramasinghe asserts that the Rosetta comet has alien life and that, in fact, most of the comets in our own stellar neighborhood are virtually teeming with microbial life. Obviously, these are some pretty staggering claims, so it seemed like a good idea to have other experts weigh in on the matter.

Enter Nathalie Cabrol. Cabrol is a planetary scientist and astrobiologist at NASA's Ames Research Center. She is a Principal Investigator at the SETI Institute (the Search for Extraterrestrial Intelligence), and she is an expert on extreme forms of life. In light of Wickramasinghe claims, I reached out to her to talk about comets, life, and whether Philae could really be harboring living microbes.

Looking for Life on 67P:

Home to aliens? Comet 67P/Churyumov–Gerasimenko, a 2.5-mile-wide (4-kilometer) comet. Image credit: ESA

To begin with, there is what is, arguably, the most important question at hand: Could there be life on Philae? Sadly, but perhaps unsurprisingly, Cabrol is not nearly as optimistic as Wickramasinghe: "Obviously, nature could keep surprising us, but from our current state of knowledge, it is highly improbable." In fact, when explicitly asked about the chance of life on 67P, she says that there isn't any, "Frankly, I would say that I would be so thrilled to be proven wrong, but I will stick my neck out on this one and say that there is none."

Ultimately, a major part of the problem with the most recent claims, according to Cabrol, is that they are based on amazingly scant evidence.

I would certainly agree that finding the 'bricks of life' are likely on a comet, but this is not life. Moreover, microbes would already be a somewhat complex form of life, and I don’t see how this could happen in such an environment...This is an extraordinary claim that requires extraordinary evidence. From what I saw so far, the evidence is visual only. Many processes in nature can end up looking the same without having the same origin at all. Morphology is a very weak argument alone.

Carbol continues by noting that, although it is extremely unlikely that comet 67P actually has life, that does not mean that it is uninteresting from an astrobiological perspective, but she made it clear that it is important to have a realistic understanding of just how interesting comets are (and can be) in this regard.

I think it is fair to say that there is a consensus in the scientific community that comets carry the 'bricks of life.' You can have a large pile of bricks and never have a house. Life needs structure and a 'cement.' What I mean by that is that it takes more than having the bricks for prebiotic chemistry to transition into life. Not to mention that we still have no idea how this process happens for life on Earth because this record has been lost on our planet to geological recycling.

However, one thing we know is that, in general, biotic processes like stability and time. Granted that comets are really old, but they are some of the most unstable and extreme environments one can imagine....

I will say that they might be excellent vectors to spread the bricks of life in planetary systems. To develop, life still needs time and stability, and a favorable environment. Comets cannot provide two out of three of these parameters, therefore, until proven wrong - I would say that comets may contribute to the distribution of the bricks of life in planetary environments, but they are poorly suited to provide a favorable environment for its inception, development, or survival.

And because of this instability, even if life did end up on a comet (as a result of a planetary fragmentation due to a massive collision, for example), Cabrol states that it wouldn't be able to subsist very long, "Personally, this is one of the last places I would think about for life to get started or to survive if, by some incredible twist of the imagination, it ended hitchhiking on a comet. The sink holes and jets observed by Rosetta are a clear mark on this instability, not to mention that these celestial bodies spend most of their lives in the coldest and darkest places of the Solar System. These conditions are not really good for life either."

So. For now, when looking for alien life, it seems that it would be a better idea to focus our efforts on more likely candidates, like Europa, Enceladus, and Ganymede.

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