A yearly meeting of the Astrobiology Centre of the Stockholm University took place this month in Tällberg. Its sessions covered topics ranging from habitability of planets of red dwarfs, reactions of ions in planetary atmospheres, or resistance of organisms to radiation, to astrobiology outreach and education, isotopes as biosignatures, and impacts and their role in evolution. I had the opportunity to attend the meeting thanks to the Czech Centres and the FameLab contest (more on that here – in Czech).
The meeting itself took place in Tällberg, in the Delacaria Hotel, and it was a great choice of venue. There was a very good conference room, great food, a chance to shortly go swimming to the spa between lectures and dinner, and most of all the town is inside the Siljan impact crater, which makes it an excellent location for any astrobiology, astronomy, geochemistry, geology or paleontology-related meetings. On the final full day of the meeting, we went to see the exposed inverted rock layers, natural oil leaks and a quarry very good for fossil hunting (which I can confirm from personal experience).
I’ll first cover the outreach session, where I presented the state of astrobiology education and outreach activities in the Czech Republic – which can seem like a lot given that we have university classes, a seminar, many popular science articles (both standalones and serials in print as well as online venues), budding collaboration with several local organizations and the occasional talks at conventions, science festivals and elsewhere; but we need to give it more shape, connect it all together to a greater extent and improve its reach as we add more activities, otherwise the impact is rather limited. Some comments at the meeting were very inspiring, and there seems to be a chance of cooperation with the planned European Astrobiology Institute, which would be amazing.
Wolf Geppert (Stockholm University; SU from now on), who organized the meeting, spoke about activities of the Astrobiology Centre, founded in 2011 in Stockholm, and the Erasmus+ program “European Astrobiology Campus”. It’s very impressive what they’re doing: Just the number of summer schools throughout the years and most of all the engagement of students attending them (who are encouraged to continue the work started there if they’re interested) is astonishing. Then there are the scientific conferences such as “The Early History of Planetary systems and habitable planets” (Tartu, Estonia; Aug 8-10), or “Geoscience for understanding habitability in the solar system and beyond” (Furnas, Azores, Portugal; Sept. 25-29), co-organized by Professor Geppert from the Astrobiology Centre.
The Time Trek was presented by Kirsi Lehto (University of Turku). I expect you know planetary trails (like the one Kosmo Klub is building in Prague!); this, on the other hand, is a time travel trail from the Big Bang to the present. They are preparing a bit gamified interactive presentations to be accessible online and planning some exercise materials for schools as well. They’re also having a summer camp (mainly for undergraduate students) in Kaarina, Finland, in late August, titled Deep History of Universe, the Earth and the Biosphere. The participation deadline is May 31, so if you’re interested, better act quickly! (Mea culpa; I meant to finish this report sooner.)
A nickel for your thoughts on Enceladus
All the sessions were helpful and inspiring; however, by far the most interesting session of the whole meeting was the one about isotopes as biosignatures. Anna Neubeck (SU) talked about using nickel isotopes as reliable biosignatures for recognizing microfossils. Nickel is an important constituent of especially some methanogens’ biochemistry. Some species have up to five Ni-using enzymes. Nickel levels thus affect methanogens’ metabolism, visible in rates of CO and H2 consumption (Neubeck et al. 2016). Methanogenic archea and some bacterial species were analyzed so far in a couple of studies; no eukarya. It would be desirable to know to what extent nickel fractionization occurs in more groups of organisms (although as far as I’ve found, the only really widespread Ni-using metalloenzyme is urease). More e.g. here.
Why use nickel as a potential biosignature? The more data we have, the more reliable results we can get. Carbon is most widely used for assessing whether a found sample is of biogenic origin, since life preferentially uses the lighter isotope (12C) and thus fractionization occurs, but this method has several caveats. First, the variation in the extent of carbon isotopes’ fractionization is huge between different groups of organisms. Second, some samples could have gone through biogenic fractionization multiple times (which would increase the signal but possibly confuse its source), and other processes may have also interfered. Sulfur is also widely used, but also has its limitations. Metals used in biogenic reactions, such as nickel, may provide another useful piece of data, though limited in other respects. I’ll certainly follow Dr. Neubeck’s research more closely. It has been proposed to use this approach for Martian samples in the future (and perhaps exoplanetary tissue ejecta? Could we get enough spectral resolution to identify isotopic ratios in such dust disks? It is certainly an enticing possibility!).
What I find especially exciting is the potential to study biogenic metal isotopes’ ratios on Enceladus. Moreover, Enceladus is approx. half water (liquid and solid), half rocky core. The core is likely porous, explaining why tidal heating of the moon suffices to keep its subsurface ocean liquid. What is the composition of the core, and how would it bode for life? Methanogens thrive in cold hydrothermal seeps whose presence on Enceladus is strongly implicated by the occurrence of hydrogen in the plumes and silica nanoparticles in the icy grains in the E ring. The detection of hydrogen made a big splash in media, but a in commentary of the original Waite et al.’s paper, Jeffrey Seewald noted: “The accumulation of H2 in the Enceladus ocean is conspicuous in the context of an Earth analog, where H2 delivered to oxygenated oceans from submarine hot springs is rapidly consumed by pervasive microbial populations in seawater. Is the presence of H2 in the Enceladus ocean an indicator for the absence of life, or is it a reflection of the very different geochemical environment and associated ecosystems on Enceladus?” If we find no signs of life when future missions visit Enceladus, its absence might be tied to the availability of certain metals (which would, however, remain a hard-to-test speculation even if we find ourselves a bigger N). That, it turn, might point toward the hot vents or deep crust possibilities of origin of life on Earth.
“Difficult enough on Earth”
Brett Thornton (SU) summarized how difficult it is to estimate the contributions of various sources and sinks of methane on Earth – let alone other objects where different processes may play a role. While the amount of methane in Earth’s atmosphere has been increasing for quite some time, the year-to-year variations are huge, and natural sources are not particularly well-mapped. Estimates from top-down (start with the overall abundance and assess how big are likely contributions from different sources) and bottom-up (start with measurement from different sources, calculate resulting overall abundance) approaches don’t match very well. Can it be because of methane consumption, lack of measurements of gas dissolution from bubbles before they get from the seeps to the sea surface, or some other factor? It will likely be a combination of various factors.
On Mars, methane’s abundance seems to be changing seasonally. There are several basic options of how it can be produced: 1. biology (most exciting, least likely), 2. geochemistry tied to hydrothermal sources (also very exciting), 3. release from earlier formed clathrates, 4. UV-driven chemistry on dust grains containing catalysts enabling the conversion of carbon dioxide to methane (see e.g. Civiš et al. 2016; also exciting since it would imply very interesting chemistry not just on Mars, but plenty other objects as well, including Venus – could such reactions be responsible for some of the chemical disequilibria in the Venusian atmosphere?).
In the discussion, I asked about the possibility of existence of subglacial lakes under Martian polar ice caps. It should be possible in theory, and it has been suggested several decades ago; however, there is no evidence of their presence as of yet (as referenced in Cockell et al. 2011, p. 133). This paper seems like a nice example of how we can model subglacial lakes’ stability on Earth. To cite some of the factors influencing it (Pattyn 2008, p. 358-9): “According to the model simulations, geometric effects such as ice thickness, mean surface slope, ice viscosity (hence ice temperature) and lake size play an important role in the stability of subglacial lakes. They favor the a priori existence of subglacial lakes near ice divides in areas of low viscosity and low surface slopes. Lake filling might therefore happen when the ice sheet is in full expansion during sustained cold periods and when surface slopes are very low, such as a glacial period. During interglacial periods, the smaller and warmer ice sheet characterized by slightly higher surface slopes in the interior facilitates lake drainage. This may explain why subglacial lakes are not observed below the Greenland ice sheet. Several reasons can be put forward, such as the lack of suitable subglacial basins or cavities to collect the subglacial water. Another factor might be given by geometry: the Greenland ice sheet is generally warmer than the Antarctic ice sheet (hence lower viscosity), thinner at the interior and characterized by higher surface slopes as the ice sheet is substantially smaller than its Antarctic counterpart.” These factors would need to be better understood to make (or discard) the case for Martian subglacial lakes. Nevertheless, it seems that their presence probably cannot be discounted as of yet.
Nevertheless, there are potential subglacial volcanoes on Mars. Some hydrated minerals may provide indirect evidence of previous hydrothermal activity in future research in-situ. Moreover, such sites may have provided conditions for life in the past, perhaps up to the present. But to return to Martian methane (forgive me the slight detour), potential discovery of such active sites alone would not answer the question, since both geochemical and biogenic activity in this kind of environment can produce methane here on Earth. It’s also likely that methane on Mars is not produced by a single source – it may be UV-driven catalytic reactions on dust grains, it may be geochemistry tied to hydrothermal activity… ESA’s TGO should provide more data on the abundance of methane (and its seasonal changes) in the Martian atmosphere, and perhaps that will help us zoom in on some of the sources to test them directly later.
Nolwenn Callac (SU) studies biogenic iron fractionization and showed her results from the Guaymas Basin site in the Gulf of California. She was looking at iron isotopes’ ratios in iron-reducing organisms living in sediments (six species in total, both bacteria and archea). There was a slight relative increase of 56Fe, as expected. However, microbial communities in chimneys and mats didn’t possess this signature, despite similar composition of iron reducers in these communities, and more resembled abiotic samples. It may be because other species mainly used fermentation as their energy source, and so didn’t leave this isotopic trace. Some species, such as Geoglobus, are capable of iron reduction but can switch to fermentation should the environment allow it. Perhaps it may be a useful model of early life’s metabolism. Like nickel, iron can be useful for testing whether disputable samples are of biological origin, although it’s insufficient alone. Again, like any indirect method, it wouldn’t be 100% reliable, but it would be beneficial nonetheless.
What about looking at morphology to provide additional information to isotope analysis (or rather inspire us to look for isotopic biosignatures in a particular sample at all)? That will be the PhD thesis topic of Diana Carlsson (SU), who summarized the topic and some issues with microfossils’ morphology. She will be working with colleagues who will focus on chemical analysis and trying to prepare a microfossil catalogue. However, would that be useful outside of Earth? We already know how deceptive (or rather inconclusive) morphology alone can be in Earth rocks as well as Martian meteorites, and chemical signs on a world with different geochemistry would have to be taken with a grain of salt.
Heavy isotopes and life
The final talk of the session was titled “How stable isotopes affect life on Earth and other planets”, delivered by Roman Zubarev of the Karolinska Institutet. At the start of his talk, Zubarev also – unrelated to the main topic – mentioned results of an upcoming study focused on trying to test the hypothesis of nanocell assembly theory of the origin of life by lysing cells Deinococcus radiodurans, separating different sorts of components (lipids, proteins, nucleic acids), and then putting them back together in different combinations. According to his presentation, the vials with liposomes, nucleic acids and a little proteins gave rise to functioning metabolism. If the results hold up to scrutiny, it will be intriguing. However, I cannot say anything about it without seeing the methodology and complete results, which won’t happen until it’s published (should be upcoming in the Discoveries journal). From what I gathered in a later discussion with the author, he performed proteomic analysis of the vials’ contents, but not sequencing or actually looking for living cells, and proteomics alone seems to me like it doesn’t conclusively show any living cell assembly. I would certainly like to see more data corroborating such an extraordinary claim. But it’s hard to speculate about something without seeing the actual paper.
The main part of his talk was about isotopic resonances and how they might affect life. I was not familiar with the concept before and I’m not entirely sure I understand it now, so I’ll refer you to Zubarev’s related papers e.g. here (the original paper concerning the isotopic resonance hypothesis), here (a nice summary of the effects of isotopically abnormal diet on living organisms + tests of the resonance hypothesis on published data) or here (proposed nonlinear effect of heavy isotopes on the pace of chemical reactions, explained here by the resonance hypothesis and tested on shrimp and bacterial growth rates). That different isotopes affect living organisms differently has been pretty clear for many decades in case of deuterium, less clear but likely in case of other heavy isotopes of biogenic elements; however, the results in the second study are interesting in their own terms, and seem to indicate that the resonance hypothesis may play a role. However, I have no idea what mechanism would be causing it, whether it can’t be just a statistical artefact (but how would that tie with the shown results?), or not an artefact, but an accident. No mechanism has been proposed up to date, as far as I know. Later at dinner, I had a chance to join a conversation with Dr. Zubarev. It was a very interesting and intellectually stimulating one, although it didn’t answer the questions I had about the work. It would be nice to see some results about purely abiotic reactions to test what is the relationship of possible isotopic resonances with reaction kinetics.
Based on my (sparse) knowledge in these subjects and my general impression of the talk and later conversation, I’m not convinced, but I don’t have the expertise to go deeper, and I’m curious about what future studies tell us and whether a mechanism is found. Should the hypothesis prove correct, it would have an impact on in situ resource utilization for biological purposes in colonizing other solar system objects – after all, varied concentrations of heavy isotopes of hydrogen and nitrogen in Xie and Zubarev (2017), mimicking conditions on Earth, Mars and Venus, produced different outcomes in E. coli growth and other parameters, with Venus-like conditions coming across as the worst. On the other hand, we need to take differing isotopic compositions of other objects into account even if the resonance hypothesis proves incorrect, since the detrimental effects of high deuterium concentration are well-known.
Noisy stars, Mars analogues, yummy impact glasses, impactors and more…
I wish I could summarize the whole meeting in more detail, but since that would make its post several times longer, I’ll at least shortly mention a few other talks. Simon Eriksson (SU) highlighted the challenges of finding exoplanets around noisy stars and what are the timescales for different phenomena that could potentially be mistaken for planets. Sebastian Sjöström (Royal Institute of Technology) talked about responses of halophilic archea on Mars-like conditions (brines of different composition, concentration, temperature and UV radiation; not with an analogue atmosphere, however), which was very interesting. In general, archea in dessicated samples tended to survive irradiation better.
Under the title “What does impact glass taste like?”, Kalle Kirsimae (University of Tartu) summarized the current state of knowledge on possible microbial alteration of volcanic glass – tubular and granular alterations, microfossils. Quite varied endolithic communities can exist in this kind of environment, and it has been speculated that volcanic (or impact) glasses may have constituted protected habitats on early Earth. To become a suitable substrate, the glass needs to be porous (and higher shock typically means higher porosity), and contain energy sources (such as FeIII) and nutrients (in which a pristine glass is depleted). Judging by impact glasses such as those in the Lonar crater, impact glass seems suitable for the development of endolithic microbial communities. More e.g. in Cockell et al. 2002.
Maria Gritsevich’s (University of Helsinki) talk “Consequences of meteoroid impacts based on atmospheric trajectory analysis” focused on an approach that enables us to both calculate the trajectory (important for assessing the impactor’s origin) and the site of impact with a very high precision even with the often very incomplete observational data. It was already successfully used. Moreover, these calculations also exist for the case of Mars (unpublished so far, which would hopefully change soon).
Wrapping it up…
Sweden in general was beautiful. I wrote a part of this summary on trains from Tällberg to Göteborg, as an idyllic sunny landscape of at first wetlands and forests, then meadows, lakes and small woods was passing by. In Stockholm, I took countless pictures of the picturesque narrow alleys of Gamla Stan, admired the Vasa and loved the Skansen; in Tällberg, there was the amazing view at the Siljan lake and the sunsets above it, and beautiful trails for walking and running; in Göteborg, I visited the Universeum (worth visiting) and the Maritime Museum (definitely worth visiting), and went for several walks around the city (during which I almost walked right into a wedding photograph and concluded that there is something inherently funny about people in long robes and tuxedos climbing atop cannons). Alas, I missed the famous fish market, because it’s closed on both Sundays and Mondays. I’m also not sure if I can ever again trust Norwegians with weather forecast for Sweden. Anyway, if you find yourself there, do not ever leave without a raincoat or an umbrella, even if the forecast promises a sunny day. (And don’t make the mistake of expecting that a waterproof jacket remains waterproof for long in Sweden.)
I participated in the Vetenskapsfestivalen in Göteborg, and I was a part of a panel discussion (recorded here) on future human society and relationships (organized by the great SF Bokhandeln, where I also talked about Czech SFF for an upcoming podcast and where a xenomorph nearly ate me, had I not escaped into the TARDIS in time!), and I had a talk about how science and SF can influence each other.
I have the Czech Centres to thank deeply for enabling the whole stay, and the FameLab contest (organized chiefly by the British Council in the Czech Republic) for giving me that option, since my stay in Sweden was a part of the Czech Centres’ Award that I won in the contest’s national finale last year. Hopefully, it’s just the beginning of my cooperation with the Czech Centres, and I will be more than happy to present Czech science and culture in the world if such opportunity arises.
Finally, Czech readers can look forward to a more in-depth popular science coverage of isotopes as biosignatures either in Vesmír, or in Astropis magazine some time later this year (stay tuned; I still have many resources to go through and then need to actually write it alongside trying to finish a novel and a few long-delayed papers). In the meantime, see you at Eurocon and EWASS in the foreseeable future!
Update: The Deinococcus paper was published and can be accessed here. I’ll provide a short summary once I have time to read it. So far, I glanced at it and spotted several misplaced capitalizations. My proofreader’s eye hurts.