Astrobiology is a field of science that investigates the origin and evolution of life, and its possible permutations elsewhere in the universe. As far as the former aspect is concerned, it is not at all an original research program. Most of what counts as astrobiological research is routine abiogenesis research, historical geology, palaeontology, geochemistry, and extremophile research. The Astrobiology Primer 2.0 and other “Astrobiology 101” resources (e.g. Cottin et al. (2014)) double as great introductions to these subjects.
The breadth of research conducted nowadays under the astrobiology banner is astounding. Astrobiology as a field is more of a mosaic of disciplines than a chimera – it is a lot of little bits put together to make a picture, not a living discipline with its own characteristics. For example, a lot of the modern research into the deep biosphere is microbiology and geochemistry, but it gets co-opted and furthered by astrobiology for its own purposes.
But for the most part, astrobiological research is just a rebranding of normal research from other fields.
This co-option is the original feature of astrobiology. All the research gets framed and extrapolated from in such a way as to make it sound as if it’s relevant to the search for life elsewhere in the universe. It’s a noble pursuit, but in my opinion, it’s not going to yield much.
For example, check out Taubner et al. (2015), a great paper reviewing the characteristics of methanogenic Archaea. However, it ends with this paragraph:
The potential of methanogens for astrobiological studies is still a long way from being exhausted. Better understanding of the Solar System bodies will give us the chance to improve the experiments. Therefore, we would recommend a interdisciplinary collaboration among the various scientiﬁc ﬁelds of astrobiology to move closer to the ultimate goal: the detection of extraterrestrial life.
Another example paper is grandiosely entitled The Last Possible Outposts for Life on Mars. It goes into a lot of detail about dessication tolerance in Terrabacteria, the earliest colonisation of land in Earth’s history, desert ecology, and other very interesting topics. The entire point of the paper, however, is to discuss how ecological successions happened on Mars, complete with pretty diagrams… when we still have no evidence at all that there even was ever life on Mars.
Röling et al. (2015) look at the effect of mineralogical substrate on biomarker preservation. This is great for palaeontology, but instead of concentrating on that, they talk about how the biomarkers will be affected on Mars, as if Mars has/had photosynthetic organisms (not such a stretch) using the exact same biochemical pathways (nope) that would leave behind biomarkers of the same chemical compositions as Earthly organisms (nope).
Life on Earth is very diverse, but it ultimately just has one phylogenetic root (Theobald, 2010). All the extremophilic bacteria, archaea, and eukaryotes that are held up as examples of how life can survive in inhospitable environments are all derived from the same evolutionary stock, the one that had its beginning in the very specific conditions of the hydrothermal vents of Archean Earth.
The fact that tardigrades can survive a short while in outer space doesn’t give us any information at all about extraterrestrial organisms, it just tells us that tardigrades, for whatever purpose (if any), evolved extreme hardiness to environmental conditions.
Deinococcus radiodurans surviving 5000 Gy of radiation (Moseley & Mattingly, 1971) says exactly the same thing, since its ability to do that is based on unique DNA repair mechanisms (Blasius et al., 2008) and we don’t have any evidence that extraterrestrial life will have any DNA to repair.
Growing Bacillus in salty culture has no relevance to Martian life. You won’t get any insights on life on Europa by looking at Lake Vostok.
Such studies are done in order to get an understanding of habitability, an astrobiological concept that’s supposed to point to where life could exist or could not (Cockell et al., 2016). But it is clear that the concept of habitability is limited only to the tolerances of Earthly organisms, and cannot take into account any potential extraterrestrial biochemistries. At the very least, the lifeforms of other planets will have adapted to the extreme conditions on those planets, and investigating Earth organisms is irrelevant.
In other words, the concept of habitability is great, if you want to look for places on Earth to find new and weird organisms, but it won’t help you much to find life elsewhere. It can also help for terraforming planets for colonisation, I guess.
These are important points to make, because we have no guarantee that life elsewhere in the universe will run the same way it does here. Think of the problems we have in even defining Earthly life. Half of our definitions make fire and crystals seem alive (they grow! They reproduce!). Others bring up evolvability, metabolism, and/or cellularity, all abilities that came about after the macromolecules that make up currently known extant living organisms on Earth (DNA, RNA, lipid cell membranes, etc.).
In other words, our definition of life and of organisms is very distinctly Earth-based. This leaves open the very real possibility that if we eventually colonise other planets, they may be teeming with their own lifeforms but we just won’t recognise them. So when, for example, you read an article entitled “Lipids as Universal Biomarkers of Extraterrestrial Life”, you can be sure that despite the strong arguments for the biological nature of lipid membranes, it’s still based on the simple assumption that life elsewhere in the universe will be similar to life on Earth, and will use lipids in any way.
It’s not a bad assumption to make, but it’s not a well-founded one either. This is a well-known problem, commonly acknowledged in astrobiology. The most common response is that since life on Earth is the only data point we have, it is the only source of information we can use to try and search for life elsewhere. And so we have initiatives looking for water on other planets, as if that’s a reliable marker of life. It very well could be, but all we have is one data point to back that up, and you don’t need to know statistics to know that that’s ridiculous.
Similarly, carbonaceous material is reliable evidence for biological activity in the Earthly fossil record (Schopf, 2006) because life here is carbon-based. There is no real reason to assume it will be similar on other planets based on this one data point. Of course, there is the retort that it’s very easy to look for carbonaceous material, given its characteristic Raman spectrum (peaks at 1350 and 1600 cm-1), so what’s the harm in doing it? This is a valid point, but it doesn’t solve the philosophical issue that the reason why we would even look for carbonaceous material or water specifically to find life is a reason underlain by too many assumptions.
There is also the fact that organic matter and hydrocarbons are found in interplanetary dust and meteorites, meaning that any putative finding of an organic biosignature will have to be shown not to have any astronomical origin.
What is even worse is looking for hints of life in atmospheric compositions, as if we must expect that life on other planets will also have evolved similar metabolic and excretory pathways as Earth organisms, or even photosynthesis. Remember that photosynthesis is a character of only one single lineage, the Plantae. Moreover, its success was an endosymbiotic accident, and it also caused a mass extinction.
What does make sense is to search for traces of physical biological activity. For example, we can look for petrological alterations from potential microbiological activity, or even tracks and ichnofossils. This is very prone to pareidolia, but at least the potential causes of a weird sedimentary or petrological structure on Mars can reliably be investigated using models and experiments that do not require an assumption of Earth-like biology.
There is already research along these lines, see e.g. McLoughlin & Grosch (2015), and I find this a much better use of astrobiologists’ time. Even stromatolite and microbialite-like structures, while also a phenomenon tied to Earth biology, are more useful as potential biosignatures (Ibarra & Corsetti, 2016). But then that wouldn’t be so much astrobiology as it would be astrosedimentology.
I must emphasise that these problems are acknowledged within astrobiology (e.g. Davila & McKay (2014)). However, there is still such silliness as the following of Kardashev’s scale from 1964, which proposed a classification of extraterrestrial societies based on their technological level (because of course evolution will direct a lineage to develop human-like intelligence, despite the numerous physiological and anatomical prerequisites that led to its development in humans!). Thinking that the Drake Equation is a scientific hypothesis and not just a (silly) thought experiment is still common.
Some point to these as simply the vestiges of the old overexcited SETI initiatives of the 1950s and the 1960s (think Morrison, Bracewell, Cocconi…). However, the fact is that they’re still discussed in a non-historical context in astrobiology journals, when they’re nothing more than the basis for hard sci fi novels.
Here’s a paper that uses complex mathematics to try to find the probability of interstellar travel in aliens. Aliens that we don’t even know exist! “Assessing the Possibility of Biological Complexity on Other Worlds, with an Estimate of the Occurrence of Complex Life in the Milky Way Galaxy” calculates probabilities of finding life on different planets based on a made up Biological Complexity Index. Here’s another one with the cool title of Alien Mindscapes, discussing the probabilities of intelligent aliens. This is all peer-reviewed stuff, not junk dug up from the fringes of the ArXiv! Just like the old SETI stuff, these papers based on nothing but speculation, and equivalent attempts to pull numbers out of thin air would be laughed at in any other field, but seem to be okay in astrobiology.
Especially the search for intelligent life, while clearly the most interesting type of life (for marketing purposes), is littered with fallacies. The most egregious of these is a really bad argument of convergent evolution, that convergent evolution will lead to intelligence, somehow. It is similar to the argument that alien life must be complex, just because a handful of lineages on Earth independently evolved multicellularity and three of them happen to be super successful (fungi, plants, animals). Both of these ideas stink of the outdated notion that evolution has a direction, when all the evidence points to the fact that it is undirected.
There is absolutely no reason in suggesting that life must evolve to more complexity, let alone multicellularity. If anything, the diversity of life on Earth shows that overwhelmingly, simpler is more successful. Sidenote: let’s not forget that cellular life might also be an Earth-only phenomenon! The whole idea of intelligent alien life is nothing more than a marketing fantasy.
The AstRoMap (European Astrobiology Roadmap)’s five research topics are:
- Origin and Evolution of Planetary Systems;
- Origins of Organic Compounds in Space;
- Rock-Water-Carbon Interactions, Organic Synthesis on Earth, and Steps to Life;
- Life and Habitability;
- Biosignatures as Facilitating Life Detection.
If we accept the view that Earth Life is unique (i.e. has one phylogenetic root that has its origin here), then most of these research topics become moot in terms of the search for life in the rest of the universe.
- The origin of planetary systems is useful to know, since any lifeform will be bound to its planet and that planet’s geochemistry.
- Origin of organic compounds in space assumes that life will use organic compounds.
- The steps to life on Earth are not necessarily informative for the origin of life elsewhere.
- Life and Habitability must have a parenthesis after it saying, “assuming that Earth extremophiles will evolve convergently on other planets even though their evolution here was mostly a matter of chance.”
- We cannot go around looking for biosignatures if we don’t know how the bio part could even work.
In other words, I don’t see much improvement from the days of exobiology, despite the copious and thorough rebranding. Astrobiology is the successor of the early NASA exobiology program, invented after an internal reorganisation in the 1990s (Dick & Strick, 2004). In fact, all the old arguments against exobiology are still just as applicable to the more extravagant claims of astrobiology. Read Simpson (1964), Mayr (1993), and Kukla (2001) for some good critiques of SETI. Read this 2014 series of Q&As with some of the world’s top astrobiologists and genuinely awesome scientists. Make up your mind about how hyperbolic astrobiological claims are.
As a final note, I just want to say that my negative attitude towards astrobiology comes out of a desire to see it succeed. Scientific astrobiological studies (i.e. anything that doesn’t mention extraterrestrial life) are genuinely great and cutting edge. The field’s name is misleading, given that we don’t know of any biology among the stars yet, but that might change sometime. Plus, I work in advertising, so it would be hypocritical of me to complain about strong branding. My big gripe is merely with the excessive speculation that is present in astrobiological papers, and the credulous positive attention it always gets.
The best thing about astrobiology is that once you strip out the astro parts of the papers, they serve as great reviews and syntheses of current microbiological, geological, and planetary science research. Let’s leave the biology grounded on Earth and ignore other planets until we actually have a potential organism to study.
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