Oral presentations and abstracts

Abstract

During the evolution of life on Earth 3.8 Gyr ago, the Earth was heavily bombarded to impact events, like Late Heavy bombardment, bombardment by comets, meteorites, and asteroids that delivered necessary life ingredients such as amino acids to the Earth which are the basic building blocks of life^1,2. The famous Miller’s experiment also demonstrated the possible mechanism for abiotic synthesis of amino acids under prebiotic conditions on the Earth³. However, there is little information available on the subsequent steps, i.e., the formation of polypeptides, which play a critical role in mediating cellular structure, function, and interaction⁴. The presence of impact craters on planetary bodies remind the role impact events may have played in Solar System formation and evolution. The impact-induced shock in such events could be a profound source for complex chemistry to occur on planetary bodies. Previous studies suggest that such a process can synthesize biomolecules such as amino acids, nucleobases and peptides^5-7. However, the role of impact processes and its subsequent steps, in prebiotic evolution are poorly understood. In the present investigation, we performed a series of experiments to study the effect of impact shock on amino acids.

We exposed various single amino acid and as well as mixtures of amino acids containing two, four,   eighteen and twenty different combinations, to strong shock waves at different Mach number ranging from 4-6 with reflected shock pressure of about 12-40 bar and temperature of about 2500 K-8000 K (estimated) for 1-2 ms time scale utilizing shock tube facility at IISC Bangalore and PRL Ahmedabad, India. Infrared signatures of shock processed solid residue revealed the signature of peptide bond on exposure to impact shock. Analysis using electron microscopic analysis provided insights into the structure and self-assembly of the formed peptides. The SEM micrographs of shock processed residue suggest that amino acids polymerized to create ordered arrangments containing twisted and folded threads, floral structures, globule, and tubular structures with complex textures (Fig 1). We performed a series of experiments containing the various amino acid mixtures at various shock conditions. A variety of structures were observed with a different combination of amino acids. The developed structures in shock processing of amino acids have striking similarities with various supramolecular structures possessed by peptide assemblies⁸. Our results are the first detailed report on the synthesis of self-assembling peptides from simple amino acids using an impact shock generated in a shock tube.

We know life as a chemical building block of organic molecules. Molecules such as amino acids are considered as essential precursors of life and are known to be synthesized in various astrochemical environments. However, the prebiotic origin of biological structures containing proteins or polypeptides, nucleic acids, lipids, etc., which are the necessary component of cellular life, is still missing. Our experiments provide a possible route for the formation of complex macroscale structure that shows the evidence for the evolution of the building blocks of life under impact shock condition and provides new insights into the potential role of impact-driven shock processes in prebiotic evolution.

References

1. Chyba, C. F., Thomas, P. J., Brookshaw, L. & Sagan, C. Cometary delivery of organic molecules to the early Earth. Science 249, 366-373 (1990).

2. Chyba, C. & Sagan, C. Endogenous production, exogenous delivery and impact-shock synthesis of organic molecules: an inventory for the origins of life. Nature 355, 125-132 (1992).

3. Miller, S. L. A production of amino acids under possible primitive earth conditions. Science 117, 528-529 (1953).

4. Frenkel-Pinter, M., Samanta, M., Ashkenasy, G. & Leman, L. J. Prebiotic Peptides: Molecular Hubs in the Origin of Life. Chemical Reviews (2020).

5. Bar-Nun, A., Bar-Nun, N., Bauer, S. & Sagan, C. Shock synthesis of amino acids in simulated primitive environments. Science 168, 470-472 (1970).

6. Martins, Z., Price, M. C., Goldman, N., Sephton, M. A. & Burchell, M. J. Shock synthesis of amino acids from impacting cometary and icy planet surface analogues. Nature Geoscience 6, 1045-1049 (2013).

7. Sugahara, H. & Mimura, K. Peptide synthesis triggered by comet impacts: A possible method for peptide delivery to the early Earth and icy satellites. Icarus 257, 103-112 (2015).

8. Wang, J., Liu, K., Xing, R. & Yan, X. Peptide self-assembly: thermodynamics and kinetics. Chemical Society Reviews 45, 5589-5604 (2016).

How to cite: Vikram, S., Vishakantaiah, J., Krishna, J., Thombre, R., Jagadeesh, G., Bhardwaj, A., Mason, N., and Sivaraman, B.: Peptide containing complex macroscale structures synthesized in shock processing of amino acids: A pathway for the origin of life, Europlanet Science Congress 2020, online, 21 Sep–9 Oct 2020, EPSC2020-1070, https://doi.org/10.5194/epsc2020-1070, 2020.

The aim of this work is to present and discuss the results of recent and ongoing wet and in silico laboratory experiments supporting Multiple Root Genesis (MuGeRo) hypothesis already proposed in search of approaches surrounding the mysterious primeval steps of life emergence on Earth and elsewhere in the Universe. There are and have been reported many theories on how the very first life began on Earth, and also on how life itself evolved, some even say that life might have arisen on Earth more than once, and since it is hard to prove or disprove them there is no fully accepted theory.

Approaching the primordial step of life emerging and possibile evolutionary scenarios from nonliving-matter towards answering the fundamental question about when, where and how life was born on Earth I’ll discuss essential requirement for the first emergence of life on Earth and Earth-like planets. 

As examples of proto-metabolic reactions occurred in a pre-biotic hydrogel context and as a model for the emergence and early evolution of life on Earth, I'm proposing the self-organizing M4 materials, having a complex chemistry, that I’ve obtained from both some meteorites and terrestrial rocks and minerals. Moreover, they are certainly the result of several coordinated activities and only some of them can be attributed to the meteorite or terrestrial rock components.

The results so far obtained could point a way towards understanding how Earth kick-started metabolism emerged on landmass that arose from Archean oceans rather than in the depths near a deep sea hydrothermal vent. 

This work puts forward also an evolutionary scenario that satisfies the known constraints by proposing that life on Earth emerged, powered by solar radiation because the M4 catalytic activities might be a primitive form of reaction network supporting abiogenic development of life on Earth or elsewhere in the Universe. This in addition the idea that microbial or virus or early forms of life were already present in our solar system at the time of Earth’s formation so that panspermia or abiogenesis results are not rival but two complementary theories.

Concerning the role that minerals may have played in organizing organic matter rising towards life from supports to scaffolds or energy sources or molecular-level information. There are some hints concerning the role that some minerals may have played in organizing matter in its rise towards life, from simple supports to scaffolds, from energy sources to even maybe providers of molecular-level information.

The work that remains to be done is huge is there an "interfacial" path from the disorganized complexity of prebiotic and "primitive-jam" to the functional systems that have been the precursors of life? To answer this question I hope soon to analyze with systems chemists the results already obtained and they will be obtained from new weighted experiments designed in scientific cooperation.

How to cite: del Gaudio, R.: Understanding the key requirement and the conditions that sparked life on Earth and beyond:clues and new knowledges supporting MuGeRo hypothesis., Europlanet Science Congress 2020, online, 21 Sep–9 Oct 2020, EPSC2020-167, https://doi.org/10.5194/epsc2020-167, 2020.

The mathematician John von Neumann, through his work on universal constructors, discovered
a generalized version of the central dogma of molecular biology biology in the 1940s, long 
before the biological version had been discovered. While his discovery played no role in the 
development of molecular biology, we may benefit from a similar mathematical approach to find 
clues on the origin of life. This then involves addressing those problems in the field that 
do not depend on the details of organic chemistry. We can then consider a general set of 
models that describe machines capable of self-maintenance and self-replication formulated in 
terms of a set of building blocks and their interactions. 

The analogue of the origin of life problem is then to explain how one can get to such 
machines starting from a set of only building blocks. A fundamental obstacle one then faces 
is the limit on the complexity of low fidelity replicating systems, preventing building 
blocks from getting assembled randomly into low fidelity machines which can then improve due 
to natural selection [1]. A generic way out of this problem is for the entire ecosystem of 
machines to have been encapsulated in a micro-structure with fixed inner surface features 
that would have boosted the fidelity [2]. Such micro-structures could have formed as a result 
of the random assembly of building blocks, leading to so-called percolation clusters [2].

This then leads us to consider how in the real world a percolation process involving the 
random assembly of organic molecules can be realized. A well studied process in the 
literature is the assembly of organic compounds in ice grains due to UV radiation and heating 
events [3,4,5]. This same process will also lead to the percolation process if it proceeds 
for a sufficiently long period [2].

In this talk I will discuss the percolation process in more detail than has been done in [2], 
explaining how it leads to the necessary symmetry breakings such as the origin of chiral 
molecules needed to explain the origin of life.   

[1] Eigen, M., 1971. Self-organization of matter and the evolution of biological 
macromolecules. Naturwissenschaften 58, 465-523.

[2] Mitra, S., 2019. Percolation clusters of organics in interstellar ice grains as the 
incubators of life, Progress in Biophysics and Molecular Biology 149, 33-38.

[3] Ciesla, F., and Sandford.,S., 2012. Organic Synthesis via Irradiation and Warming of Ice 
Grains in the Solar Nebula. Science 336, 452-454.

[4] Muñoz Caro, G., et al., 2002. Amino acids from ultraviolet irradiation of interstellar ice 
analogues. Nature 416, 403-406.

[5]  Meinert, C,., et al., 2016. Ribose and related sugars from ultraviolet irradiation of 
interstellar ice analogs. Science 352, 208-212.

How to cite: Mitra, S.: The first step from molecules to life: Formation of large random molecules acting as micro-environments, Europlanet Science Congress 2020, online, 21 Sep–9 Oct 2020, EPSC2020-785, https://doi.org/10.5194/epsc2020-785, 2020.

Pyridine is a heterocyclic aromatic molecule of gross formula C₅H₅N where the N atom is included in the aromatic ring. The molecule as such is not abundant in nature, but its derivatives are often part of important biomolecules. For instance, it is one of the basic units in the nicotinamide adenine dinucleotide, NADH, which is an essential reducing agent in various biological processes. Interestingly, pyridine derivatives (e.g. 2,4,6-trimethylpyridine and pyridine carboxylic acids) were identified in carbonaceous chondrites [1-4] along with many other molecules of biological significance. In addition to that, nicotinonitrile (3-cyanopyridine) as well as 2- and 4-cyanopyridine have been synthesized in a version of the Miller experiment by the action of electric discharges on ethylene and ammonia, with an intermediate step being the synthesis of pyridine [5]. The possibility that nicotinonitrile hydrolyzed in the primitive ocean to nicotinamide and nicotinic acid reinforces the prebiotic potential of pyridine.

In conclusion, either formed locally on Earth from simple precursors or brought by extraterrestrial carriers, the presence of pyridine or of one of its derivatives could have played an important role in the organic chemistry that triggered the origin of life on Earth. Pyridine formation can also be seen as an intermediate step towards the formation of pyrimidine (C₄H₄N₂), a species constituting the molecular skeleton of important nucleobases (cytosine, uracil and thymine). Pyridine and pyrimidine are also expected to share similarities in their chemical behavior because of the presence of N in the aromatic ring in the place of one (pyridine) or two (pyrimidine) methine groups (=CH−).

For the above reasons, in our laboratory we have undertaken a systematic experimental investigation to address pyridine stability in the conditions of primitive Earth. In a first series of experiments, we have exposed isolated pyridine molecules to the attack of very reactive species, namely atomic oxygen and nitrogen. The aim is to verify whether the N-containing aromatic ring of pyridine is preserved after the chemical attack of reactive transient species like O and N atoms that might have been relatively abundant under the conditions of primitive Earth when the O₂/O₃ UV shield was not present yet. The employed experimental technique is the one described in Ref. [6]. The implications for the stability of pyridine and its derivatives, or of other molecules for which pyridine can be considered as a proxy, will be noted.

The Authors wish to thank the Italian Space Agency for co-funding the Life in Space project (ASI N. 2019-3-U.0).

[1] P. G.Stoks, A. W. Schwartz. Basic nitrogen-heterocyclic compounds in the Murchison meteorite. Geochimica et Cosmochimica Acta 46, 309-315 (1982).

[2] Y. Yamashita, H. Naraoka. Two homologous series of alkylpyridines in the Murchison meteorite. Geochemical Journal 48, 519-525, (2014).

[3] S. Pizzarello, Y. Huang, L. Becker, R. J. Poreda, R. A. Nieman, G. Cooper, M. Williams. The Organic Content of the Tagish Lake Meteorite. Science 293, 2236- 2239 (2001).

[4] K. E. Smith, M. P. Callahan, P. A. Gerakines, J. P. Dworkin, C. H. House. Investigation of pyridine carboxylic acids in CM2 carbonaceous chondrites: Potential precursor molecules for ancient coenzymes. Geochimica et Cosmochimica Acta 136, 1–12 (2014).

[5] N. Friedmann, S. L. Miller, R. A. Sanchez. Primitive Earth Synthesis of Nicotinic Acid Derivatives. Science Vol. 171, 1026-1027 (1971).

[6] N. Balucani. Elementary reactions of N atoms with hydrocarbons: first steps towards the formation of prebiotic N-containing molecules in planetary atmospheres. Chem. Soc. Rev. 41, 5473–5483 (2012).

How to cite: Balucani, N., Recio, P., Marchione, D., Caracciolo, A., and Casavecchia, P.: The stability of pyridine upon chemical attack under the conditions of primitive Earth, Europlanet Science Congress 2020, online, 21 Sep–9 Oct 2020, EPSC2020-402, https://doi.org/10.5194/epsc2020-402, 2020.

The amount of nitrogen present in the atmosphere at the time when life evolved on Earth is central for understanding the production of prebiotic molecules and hence, is a fundamental quantity to constrain. However, estimates of atmospheric molecular nitrogen partial surface pressures (pN₂) during the Archean widely vary in the literature. In this study, we apply a model combining newly-gained insights into atmospheric escape, magma ocean duration and outgassing evolution to derive pN₂ during the Hadean and Archean. Results suggest <420 millibar surface molecular nitrogen (N₂) at the time when life originated, which is much lower compared to previous works, hence could impact the production rate of prebiotic molecules such as hydrogen cyanide. Our revised values provide new input for atmospheric chamber experiments simulating prebiotic chemistry on the early Earth. Our results assuming negligible nitrogen escape rates are in agreement with research based on solidified gas bubbles and the oxidation of iron in micrometeorites at 2.7 Gigayear ago suggesting that the atmospheric pressure was probably less than half the present-day value. Furthermore, our results contradict previous studies that assume N₂ partial surface pressures during the Archean higher than today and suggest that if the N₂ partial pressure were low in the Archean it would likely be low in the Hadean as well. Additionally, our results imply a biogenic nitrogen fixation rate from 9 to 14 Teragram N₂ per year which is consistent with modern marine biofixation rates, hence indicate an oceanic origin of this fixation process.

How to cite: Gebauer, S., Grenfell, J. L., Lammer, H., de Vera, J.-P. P., Sproß, L., Airapetian, V. S., Sinnhuber, M., and Rauer, H.: Atmospheric nitrogen at the time when life evolved on Earth, Europlanet Science Congress 2020, online, 21 Sep–9 Oct 2020, EPSC2020-706, https://doi.org/10.5194/epsc2020-706, 2020.

Pyrite-induced uv-photocatalytic abiotic nitrogen fixation: implications for early atmospheres and Life

¹Centro de Astrobiología (CSIC-INTA), Torrejón de Ardoz, Madrid, Spain.

²Department of Computer Science, Electrical and Space Engineering, Luleå Universit of Technology, Luleå, Sweden.

  Nitrogen is an essential element for life, a prerequisite for the origin and evolution of life on Earth, or in any other potentially habitable planet. The molecular form of nitrogen, N₂, is universally available but is biochemically inaccessible for life due to the strength of its triple bond. Prior to the emergence of life, there must have been an abiotic process that could fix nitrogen in a biochemically usable form. The UV photo-catalytic effects of minerals such as pyrite on nitrogen fixation have to date been overlooked. Here we show experimentally, using X-ray photoemission and infrared spectroscopies that, under a standard earth atmosphere containing nitrogen and water vapour at Earth or Martian pressures, nitrogen is fixed to pyrite as ammonium iron sulfate after merely two hours of exposure to 2,3 W/m2 of ultraviolet irradiance in the 200–400 nm range [1]. Our experiments show that this process exists also in the absence of UV, although about 50 times slower. The experiments also show that carbonates species are fixed on pyrite surface [Figure 1]. We conclude that UV photocatalysis on pyrite may have been a natural mechanism of prebiotic fixation of nitrogen into ammonium sulfates which is then easily released upon contact with liquid water. This property of pyrite may have been incorporated naturally in the prebiotic chemistry evolution, leading to the inclusion of pyrite nano-clusters as reaction centres to generate ammonia from nitrogen, and then from ammonia to generate ammonium sulfates salts in the presence of oxygen. This process has furthermore implication for the abiotic nitrogen fixation on other planetary environments, and it has critical implications for the habitability of planet and the origin of life.

Fig. 1    Picture of the Planetary Atmosphere and Surfaces Chamber and XPS spectra of the presence of ammonium sulfate on pyrite surface (on the left). Schematic representation of the processes that lead nitrogen fixation on pyrite surface (on the right), (i) by UV photo-catalysis under low pressure conditions (on the top) and, (ii) by the catalytic effect of iron oxide-iron sulfide tandem under visible light conditions and standard earth atmosphere (on the bottom).

[1]   E. Mateo-Marti, S. Galvez-Martinez, C. Gil-Lozano and M-P. Zorzano, Scientific Reports, 9, 15311 (2019)

How to cite: Mateo-Marti, E., Galvez-Martinez, S., Gil-Lozano, C., and Zorzano, M.-P.: Pyrite-induced uv-photocatalytic abiotic nitrogen fixation: implications for early atmospheres and Life, Europlanet Science Congress 2020, online, 21 Sep–9 Oct 2020, EPSC2020-760, https://doi.org/10.5194/epsc2020-760, 2020.

Abstract

One of the most interesting aims for the study of exoplanets to understand under which conditions life could appear and survive in other environments. To be able to bear any form of life, “environments must provide extended regions of liquid water, conditions favorable for the assembly of complex organic molecules, and energy resources to sustain metabolism” (NASA Astrobiology Roadmap, Goal 1). To satisfy this requirement, specific physical and atmospheric conditions must be met. Those are extremely entwined with one another, so a quantitative assessment of the actual habitability of a planet is still hard to infer.

In this contribution, we discuss some self-consistent models of potential atmospheres of currently known terrestrial exoplanets, to understand which thermodynamic conditions would potentially allow the appearance of life on their surfaces. We also motivate how such theoretical projects should be linked with the reality of nature and future observations of exoplanetary spectra. We then specify the reasons why the theoretical determination of the spectral features that could be used to trace habitability (and life) is, therefore, essential now more than ever.

Context

Exoplanetology is one of the most flourishing fields of astrophysics. At the time of writing, more than 4000 confirmed exoplanets have been discovered, and many are to be revealed with current and future facilities.

One of the most interesting revelations was the detection of an ever-growing population of terrestrial planets, up to ten times more massive than the Earth: the so-called Super Earths. Surprisingly, the Solar System is lacking planets belonging to this class, but they appear to be common around other main-sequence stars.

The only way for an astronomer to characterize an exoplanet is through remote techniques, such as the spectroscopic analysis of its atmosphere. Spectroscopic studies of the atmospheres of Super Earths are of paramount importance to probe their composition, which could provide hints about the formation of such planets, their evolution and the conditions under which life could form on their surfaces (see e.g. [1]).

This is not a simple task with the currently available facilities since the emitted or reflected radiation coming from a planetary atmosphere is orders of magnitude smaller than the one emitted by the host star. A new generation of ground- and space-based instruments (e.g. METIS at ELT [2,3], ARIEL [4], PLATO [5], and the LIFE Mission Initiative [6,7, see also the submitted contribution by Angerhausen et al.] is currently being developed and will be able to characterize hot and temperate Earth analogues in the next years/decades. Now more than ever, a theoretical approach to the study of atmospheres of terrestrial exoplanets is necessary, to provide cross-reference tools and to set the ground for the upcoming observations.

Methods

From the exoplanet catalogue Exo-MerCat [8], a sample of all currently known Super Earths was collected.

Choosing combinations of various chemical compositions and atmospheric pressures, a grid of nearly 2400 models was computed using the 1D radiative-convective code MAGRATHEA [9]. The output produced by MAGRATHEA is the radiative-convective equilibrium pressure-temperature profile of the modelled atmosphere, provided that the input physical and chemical parameters allow for the stability of the atmosphere itself.

The code treats the absorption of each atmospheric layer through the k-correlated distribution, which is much faster than the usual line-by-line approach. It, however, requires to calculate beforehand the k-correlated table, thus limiting the space of physical and chemical input parameters and, therefore, the atmospheres that can be modelled. The chemical database currently included in MAGRATHEA is composed of CO2, O2, H2O, and N2. From a physical point of view, MAGRATHEA can treat temperatures up to 500 K and pressures up to 100 atm. It is thus possible to produce self-consistent temperate and warm Mars- and Earth-like pressure-temperature profiles by solving the radiative transfer equation directly, with no need for prescriptions or parameterizations.

Results

From the currently known terrestrial planets sample, eleven targets were selected to perform specific atmospheric simulations. Those were: LHS 1140 b, K2-18 b, K2-3 b, Kepler-48 b, GJ 1132 b, TRAPPIST-1 b, TRAPPIST-1 c, TRAPPIST-1 g, K2-266 e, K2-155 d, and Kepler-138 d.

Most of these planets are within the inner boundary of the habitable zones of their host stars [10]: these targets are, in principle, unsuitable for the appearance and survival of life on their surfaces. The presence of an atmosphere could, however, mitigate the effect caused by the higher irradiation these planets receive from their host stars -- compared to the one the Earth receives from the Sun. Hence, simulating a wide range of atmospheres for each of the selected targets is useful and informative to obtain a better understanding of the actual habitability of these terrestrial exoplanets.

We show the success rate of the models for the chosen targets in a stellar temperature vs irradiation plot (Fig. 1) and the normalized frequency of habitable, cool, or warm atmospheres for the successful models (Fig. 2).

As visible from Fig. 1, many models did not converge, due to the high temperatures that caused either too much water vapour to be produced, or that exceeded the 500 K threshold imposed by the look-up table. However, despite the irradiances being much higher than what prescribed by the standard definition of the habitable zone, some combinations of atmospheric parameters would result in surface temperatures for the selected targets that would, in principle, allow liquid water to exist on their surface (Fig. 2).

Albeit in this extremely simple form, this study has proven useful to assess quantitatively the effect that the atmosphere has on the habitability of an exoplanet, paving the way for future simulations and observations.

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[3] Quanz S. P., et al., IJAsB, 14, 279 (2015)

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[6] Quanz, S. P., et al., arXiv e-prints arXiv:1908.01316 (2019)

[7] Quanz, S.P., et al., Optical and Infrared Interferometry and Imaging VI, 10701, 107011I (2018)

[8] Alei, E., et al., Astronomy and Computing, 31, 100370 (2020)

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[10] Kopparapu, R. K., et al., ApJ, 765 (1993)

How to cite: Alei, E., Claudi, R., and Quanz, S. P.: Assessing the habitability of observed Super Earths, Europlanet Science Congress 2020, online, 21 Sep–9 Oct 2020, EPSC2020-355, https://doi.org/10.5194/epsc2020-355, 2020.

Ultraviolet (UV) irradiation on the surface of Mars is an important factor affecting the survivability of microorganisms on Mars. The possibility of Martian brines made from Fe₂(SO₄)₃, MnSO₄, and MgSO₄ salts providing a habitable niche on Mars via attenuation of UV radiation was investigated on the bacteria Bacillus subtilis and Enterococcus faecalis. Results demonstrated that it is possible for brines containing Fe₂(SO₄)₃ on Mars to provide protection from harmful UV radiation, even at concentrations as low as 0.5%. Brines made from MnSO₄ and MgSO₄, did not provide significant UV protection and most spores/cells died over the course of short-term experiments.

However, Fe₂(SO₄)₃ brines are strongly acidic, and thus, were lethal to E. faecalis. In contrast, B. subtilis, as a spore-forming bacterium resistant to pH extremes, was unaffected by the acidic conditions of the brines and did not experience any significant lethal effects. Any extant microbial life in Martian Fe₂(SO₄)₃ brines (if present) would need to be capable of surviving acidic environments, if these brines are to be considered a possible habitable niche.

The results from this work are important to both the search for life on planets with an atmosphere unable to significantly attenuate UV radiation (i.e., like Mars); and for planetary protection, since it is possible that terrestrial bacteria in the genus Bacillus are likely to survive in Fe-sulfate brines on Mars.

Furthermore, preliminary work on UV and photosynthetically active radiation (PAR) light transmission and scattering through simulated Martian regolith and rock samples are also presented. Regoliths that block UV but allow for PAR would be likely candidates for supporting bacterial life.

How to cite: Godin, P., Schuerger, A., Moore, C., and Moores, J.: UV Protection of Bacteria Under Simulated Martian Conditions, Europlanet Science Congress 2020, online, 21 Sep–9 Oct 2020, EPSC2020-59, https://doi.org/10.5194/epsc2020-59, 2020.

Summary: As part of the NASA Frontier Development Lab, we implemented a parallelized cloud-based exploration strategy to better understand the statistical distributions and properties of potential planetary atmospheres. Starting with a modern-day Earth atmosphere, we iteratively and incrementally simulated a range of atmospheres to infer the landscape of the multi-parameter space, such as the abundances of biological mediated gases that would yield stable (non-runaway) planetary atmospheres on Earth-like planets around solar-type stars. Our current dataset comprises of 124,314 simulated models of earth-like exoplanet atmospheres and is available publicly on the NASA Exoplanet Archive. Our scalable approach of analysing atmospheres could also help interpret future observations of planetary atmospheres by providing estimates of atmospheric gas fluxes and temperatures as a function of altitude, and thereby enable high-throughput first-order assessment of the potential habitability of exoplanetary surfaces.

Introduction: The NASA Frontier Development Laboratory (FDL) is an annual science accelerator that focuses on applying machine learning and large-scale computing to challenges in space science and exploration (Cabrol et al. 2018). FDL engages interdisciplinary teams of computer scientists and space science domain experts and tasks them to solve problems that are valuable to NASA and humanity’s future. We implemented a cloud-based strategy to better understand the statistical distributions of habitable planets and life in the universe and layout an avenue to characterize the potential role of biological regulation of planetary atmospheres.

We simulated a range of atmospheres to infer the landscape of the multi-parameter space, such as the abundances of biological mediated gases that would yield stable (non-runaway) planetary atmospheres on Earth-like planets around solar-type stars. Our scalable tool, once coupled to a generalized ecosystem model, could help derive estimates of the biological mediated atmospheric gas fluxes and help constrain the type and the extent of exobiology on exoplanets based on the remotely detected atmospheric compositions.

Method: Our team generated data for a wide variety of hypothetical biospheres to scope out the plausible range of habitable atmospheres and metabolisms that could be present in the universe. We implemented a cloud-based massively parallelized procedural parameter search for a wide range of planetary atmospheres. Since existing tools were not capable of broad parameter scans, we streamlined the ATMOS 1-D atmospheric simulation code developed by the NASA Virtual Planetary Laboratory (Arney et al. 2016, Meadows et al. 2016). and produced a package for the community called PyAtmos (https://github.com/PyAtmos). This package dramatically increases the usability and accessibility of the ATMOS 1-D software across a range of platforms.

We then used PyAtmos on the Google Cloud Platform in an automated and scalable procedure to search the parameter space of atmospheric compositions. Our search considered the relative concentrations of greenhouse gases such as methane, carbon dioxide and water. 124,314 different atmospheres were simulated and then analyzed to establish if the planetary surface temperatures and fluxes of gases were compatible with conditions that could maintain a liquid water inventory on the planetary surface.

Results: The dataset of planetary atmospheres we have generated can be used for training machine learning models to bootstrap the ATMOS code. It is an open-source dataset (https://exoplanetarchive.ipac.caltech.edu/cgi-bin/FDL/nph-fdl?atmos) available for the community to understand distributions of habitability parameters such as surface temperatures and free energy available to life on different classes of atmosphere bearing planets.

All of these are based around an Earth-like planet that orbits a star similar to the Sun, but with different gas mixtures in their atmospheres. A parameter space of possible atmospheres was scanned by varying the concentrations of six gases - Carbon dioxide, Oxygen, Water, Methane, Hydrogen and Nitrogen.

In future work, we plan to include parameters such as star type, planet size and distance from the host star when evaluating the range of different atmospheres that may be habitable. The scalability of our framework provides a mechanism to incorporate complex biogeochemical and global climate models to better understand the co-evolution of the atmosphere and biosphere (e.g. Chopra et al. 2016, Gebauer et al. 2017, Nicholson et al. 2018, Lineweaver et al. 2018). Analyses of such multi-dimensional datasets will enable better interpretations of future observations of exo-atmospheres and biosignatures by upcoming telescopes (Fuji et al. 2018).

References

Arney, G. N. et al. (2016) The Pale Orange Dot: The Spectrum and Habitability of Hazy Archean Earth. Astrobiology, 16(11), 873–899.

Cabrol, N. A., et al. (2018) Advancing Astrobiology Through Public/Private Partnership: The FDL Model. In: Lunar and Planetary Science Conference. Vol. 49. Lunar and Planetary Science Conference, 1275.

Chopra, A. and Lineweaver, C. H. (2016) The Case for a Gaian Bottleneck: The Biology of Habitability. Astrobiology, 16(1), 7–22.

Fujii, Y. et al. (2018) Exoplanet Biosignatures: Observational Prospects. Astrobiology, 18(6).

Gebauer, S. et al. (2017) Evolution of Earth-like Extrasolar Planetary Atmospheres: Assessing the Atmospheres and Biospheres of Early Earth Analog Planets with a Coupled Atmosphere Biogeochemical Model. Astrobiology, 17(1), 27–54.

Lineweaver, C. H. et al. (2018), The Evolution of Habitability: Characteristics of Habitable Planets, in Vera M. Kolb (Ed.) Handbook of Astrobiology, Taylor & Francis

Meadows, V. S. et al. (2016) The Habitability of Proxima Centauri b: Environmental States and Observational Discriminants. Astrobiology, 18(2), 133– 189.

Nicholson, A. E. et al. (2018). Gaian bottlenecks and planetary habitability maintained by evolving model biospheres: The ExoGaia model. Monthly Notices of the Royal Astronomical Society, 477(1), 727–740.

How to cite: Chopra, A., Bell, A., Fawcett, W., Talebi, R., Angerhausen, D., Güneş Baydin, A., Berea, A., A. Cabrol, N., P. Kempes, C., and Mascaro, M.: EXO-ATMOS: A scalable grid of hypothetical planetary atmospheres, Europlanet Science Congress 2020, online, 21 Sep–9 Oct 2020, EPSC2020-664, https://doi.org/10.5194/epsc2020-664, 2020.

High intensity shock tubes are generally used to mimic extreme conditions, of pressure and temperature, that prevail in impact scenarios. In our experiment we tried to simulate the condition of asteroid and meteorite impacts on early Earth organisms such as foraminifera. The survivability of foraminifera shells (made up to calcium carbonate) in such extreme conditions of pressure and temperature are least known to-date. There are several species of foraminifera and few species of them were subjected to the shock condition, they are the shallow benthic foraminifera Calcarina spengleri, Sorites orbiculus and deep dwelling planktonic foraminifera Pulliniatina obliquiloculata (Fig 1).

The experiment was carried out using the high intensity shock tube in PRL. The samples were subjected to shock temperatures of ~ 4000 K for 2 ms using helium as driver gas and krypton as driven gas and the foraminifera samples were kept at the end of the driven section before the end flange. After shock processing the samples were collected by opening the end flange, while physical appearance of the samples analysed by sterioscopic light microscope and it underwent powder, fragmented and turned from pure white to brown, therefore a clear indication found that the shells had undergone high temperature processing. However, it was found that certain variety of foraminiferal shells can be survive at the extreme conditions in an impact event.

Fig 1 The foraminifera species used for experiment: 1. Textularia sp., 2. Calcarina spengleri, 3. Pulliniatina obliquiloculata and 4. Sorites orbiculus

How to cite: Muruganantham, M., Surendra, V. S., Mekka, J., Bhushan, R., Mason, N., Vijayan, S., and Sivaraman, B.: Foraminiferal shells under extreme shock conditions, Europlanet Science Congress 2020, online, 21 Sep–9 Oct 2020, EPSC2020-1009, https://doi.org/10.5194/epsc2020-1009, 2020.

Abstract

Mass spectrometric measurements conducted on various amino acids that are relevant to life as we know it on Earth are presented using ORIGIN. ORIGIN is a novel Laser Desorption Mass Spectrometric setup designed for in situ operation on planetary surfaces, including the icy surfaces on ocean worlds such as Europa and Enceladus. Laser desorption measurements were conducted on single amino acids and amino acid mixtures to investigate their fragmentation behaviour at given laser settings. Simple mixtures consisting of four amino acids and a complex mixture consisting of ten amino acids at various concentrations and with components ranging from Glycine to Tyrosine are investigated. The unique fragmentation patterns observed for the single amino acids allowed successfully the identification of amino acids in the complex mixture. The measurement capabilities of ORIGIN are of high importance as ORIGIN represents an alternative instrument to traditional space instruments for future space exploration missions devoted to the detection of life.

Introduction

The icy moons Europa and Enceladus of Jupiter and Saturn, respectively, represent promising objects in our Solar System that may host life in their liquid oceans underneath their ice crust. Through cracks in the ice shells signatures of life, such as amino acids, lipids, among others, may escape the liquid oceans and form deposits on the surface, which can be probed more easily by instrumentation than in the ocean directly. However, in situ operation of instrumentation designed for the detection of signatures of life is extremely challenging and sensitive instrumentation is required to withstand the harsh environmental conditions that exist at the ice surfaces.

In our contribution, we present the current figures of merit of our newly developed laser desorption mass spectrometric instrument, called ORIGIN.

Experimental

Sample Preparation. Solutions of single amino acids (ranging from Gly to Tyr) at a concentration of 100 µM, mixtures of four amino acids (Ala, Asp, Met, and Tyr, at total concentrations of 100µM), and a mixture of ten amino acids (Gly, Ala, B-Ala, Ser, Asp, Leu, Glu, Met, His, Tyr) of a total mixture concentration of 100 µM (singles have a concentration down to 2.5 µM), were prepared and drop cast (1 µl) under atmospheric condition and at room temperature into shallow cavities (0.2 mm x Ø 3 mm) on sample holders [1].   

LDMS Measurements. Measurements were conducted using our newly developed laser desorption mass spectrometric setup, called ORIGIN [1]. ORIGIN consists of a miniature reflectron-type time-of-flight mass analyser (160 mm x Ø 60 mm) [2,3] that is coupled to a nanosecond pulsed laser system (pulse width ~3 ns, wavelength λ = 266 nm, pulse repetition rate = 20 Hz). The mass analyser is located within a vacuum chamber that is evacuated to a base pressure down to the mid 10^-8 mbar level. An optical beam delivery system guides the laser pulses from the nanosecond laser system towards the vacuum chamber, towards the lens system that is just installed outside, above the entrance window of the vacuum chamber. The laser pulses are focussed through the mass analyser towards the sample surface to induce the desorption of the analyte of interest. The sample holder that consists of cavities is placed outside the laser focus to gently desorbed the analyte (laser spot size at the level of  ~30 µm). With each laser pulse, sample material is desorbed and partially ionised. Only positively charged species can enter the entrance ion optics of the mass analyser, and are subsequently guided to the detector system. The charged species arrive in time sequences at the detector system, and a quadratic equation is used for the conversion of the time-of-flight spectra to mass spectra.

In this study, we discuss measurements conducted on single amino acids, four simple mixtures of amino acids at different concentrations, and on a mixture that consists of ten amino acids at different concentrations down to 2.5 µM level. The biofilms were sampled spot-wise by applying 100 laser shots per position. In total 40 positions were sampled on each biofilm (single amino acid, simple and more complex mixtures).  

Results and Discussion

From the measurements of single amino acids their fragmentation behaviour can be determined accurately. Subsequently, these fragmentation patterns allowed for the direct identification of amino acids in the more simple mixtures and the more complex mixture by fitting the mass spectra of the mixtures. Moreover, it is possible to simulate the entire laser desorption mass spectrometric of the mixtures.

In Figure 1 the laser desorption measurements conducted on one of the simple mixtures are shown (top panel) whereas at the bottom panel the simulated spectrum is shown. As can be observed, both spectra are almost identical to each other, which is of high importance as the simulation allows reliable identification of amino acids within a mixture.  

Figure 1: Measured (top) and simulated (bottom) laser desorption mass spectra of a simple amino acid mixture that consists of Ala, Met, Asp, and Tyr.

Summary and Conclusions

Laser desorption mass spectrometric studies were conducted on single amino acids to investigate their simple and robust fragmentation pattern and on simple and more complex mixtures of amino acids. Through simple fragmentation patterns observed for single amino acid measurements, amino acids in simpler and more complex mixtures could be identified directly. Moreover, the robust fragmentation patterns observed allowed to simulate mass spectra of amino acid mixtures. The latter is of high importance as it allows reliable post-measurement identification of amino acids. The study presented is of high importance for future space exploration missions because ORIGIN represents a promising analytical tool for the identification of signatures of life, if present, on e.g., the icy surface of Europa.

References

[1] Ligterink, N.F.W., Grimaudo, V., Moreno-García, P., Lukmanov, R., Tulej, M., Leya, I., Lindner, R., Wurz, P., Cockell, C.S., Ehrenfreund, P., and Riedo, A., Nature Sci. Rep., Vol. 10, 2020, 9641.

[2] Riedo, A., Bieler, A., Neuland, M., Tulej M., and Wurz, P., J. Mass Spectrom., Vol. 48, 1 - 15, 2013.

[3] Riedo, A., Meyer, S., Heredia, B., Neuland, M., Bieler, A., Tulej, M., Leya, I., Iakovleva, M., Mezger K., and Wurz P., Planet. Space Sci., Vol. 87, 1 - 13, 2013.

How to cite: Riedo, A., Ligterink, N. F. W., Grimaudo, V., de Koning, C., Lukmanov, R., Tulej, M., and Wurz, P.: Direct identification of Amino Acids via fragment patterns using sensitive Laser Desorption Mass Spectrometry, Europlanet Science Congress 2020, online, 21 Sep–9 Oct 2020, EPSC2020-1080, https://doi.org/10.5194/epsc2020-1080, 2020.

The notion that exoplanets are in a state of equilibrium with their surroundings has not given place to the viewpoint of transmissivity of life on the interstellar scales. Spread of human diseases and life reemergence after mass extinction on Earth might show similar characteristics of highly clustered events in space and time.                                                                      Here, we extend numerical tests of life's spatio-temporal clustering on the simple model of the Galactic patch. We use the cellular-automaton model that reproduces the hypothetical spatial and time evolution of the life spreading within a Galactic patch, adapting parameters relevant for pandemics. Such type of models highlights crucial mechanisms underlying complex behavior. Performed simulations aim to determine phase transition between the persistence and extinction of life spreading within the galactic patch. This phase space is defined by the interplay of planetary systems sterilization and life infection rates. The perseverance part of phase space is that the spreading of life will persist when the simulation parameters lie in this domain and vice versa. The realizations of phase space were calculated by simulating 100 x 100 cells network with ten independent runnings.  Each running lasted for 500 arbitrary time units with time step 1. At the beginning of each run, the lattice has been initially set with a randomly chosen sample of planetary systems from used Galactic density distribution.                                  

We observe a critical influence of mobility on regions of life perseverance, termination, and transition within the phase space. Life spreading through the Galactic patch is in at least three different geometrical shapes ('waves') differing from spherical. We set up that this phenomenon is robust, independent from the details of cyclic life termination rates. With increasing mobility above the specified threshold, these geometrical shapes ('waves') grow and saturate the patch, and they persist over a long time range. But there is no spatial pattern for mobility rate below the particular threshold, and the life spreading process is not persistent in time.                                                                                                                                                           

Based on our study, we propose that the life clustering within a specific region in our Galaxy can be reconstructed in a two-dimensional phase space using biomarkers and biosignatures data from future exoplanets extensive surveys. Also, this can be applied to the Galactic bulge habitability. Wislocka at al. (2019) calculated the possible atmospheric mass loss for 16  hot Jupiters residing in the Galactic bulge due to radiation from the Milky Way's (MW) central SMBH, Sagittarius A* (Sgr A*). They found that planets in the Galactic bulge could have lost up to several Earth atmospheres in mass during the AGN phase of Sgr A*. Bearing in mind the mass of these hot Jupiters, this fraction of atmospheric mass loss is not drastic, however for smaller, rocky planets within the bulge, such atmospheric mass loss can be essential but during the activity of Milky Way SMBH.  However, Balbi et al. (2020)  have shown that lithopanspermia scenarios would be more efficient in the bulge concerning the solar neighborhood. If the spreading of life between stellar systems is possible in such an environment, then the highest rate of life-termination events might be balanced by the possibility that life can migrate quickly to safer locations.  Thus, it will be necessary to correctly define a metric on the observable biosignatures of exoplanets within the observed Galactic region. If this metric is time-dependent, there is a good chance that life transfer is occurring.

Acknowledgements.  This work is  supported by Ministry of Education, Science and Technological development of Republic Serbia through the Astrophysical Spectroscopy of Extragalactic Objects project number 176001.

References

Wisłocka, A. M.; Kovacevic, A. B.; Balbi, A. Comparative analysis of the influence of Sgr A* and nearby active galactic nuclei on the mass loss of known exoplanets. Astron. Astrophys. 2019, 624, A71.                                                                                 

Balbi, A.; Hami, M.; Kovacevic, A, The Habitability of the Galactic Bulge. Life. 2020, submitted

How to cite: Kovacevic, A.: About metrics in phase space for detection of interstellar transmission of life, Europlanet Science Congress 2020, online, 21 Sep–9 Oct 2020, EPSC2020-242, https://doi.org/10.5194/epsc2020-242, 2020.

Introduction

Owing to the limited amount of data from other planetary bodies in our Solar System, terrestrial analogues are frequently used to further the understanding of extraterrestrial environments. One of the moons of Jupiter, Europa has been selected for future exploration in our Solar System. Measurements carried out by the Galileo spacecraft suggest the existence of a tidally heated, sub-surface ocean that could harbour life [1]; yet the composition of the ocean is unknown as there have been no direct measurements [2, 3]. The information about Europa is thus limited but has been complemented by modelling surface and interior processes [4] (fig. 1). Surface features and data from Galileo initially suggested an ocean dominated by magnesium sulfate; however, recent observations suggest it is dominated by sodium chloride with a high concentration of magnesium [5, 6, 7]. Considering the limited data available about the interior of this moon, analogue studies can be used to extend our understanding of the crucial constraints on microbial habitability below the ice shell.

To date, terrestrial analogue studies for Europa have focused on subglacial lakes, cold springs, and sulfate lakes. These sites, however, have been selected based on a single or few parameters. Some are of interest due to their pH level, temperature, or main ionic composition. This approach often ignores or compromises other important variables that may influence habitability, such as pressure, dissolved gases or minor ions. The aim of this work is to develop a quantitative method to evaluate the similarity between terrestrial analogue sites and models of the Europan ocean. This will improve the selection of appropriate terrestrial analogues, the consequent validity of the results from microbiological and geochemical studies, and thus, their correlation to studies of the potential habitability of Europa.

Objective analogue site selection requires a quantitative method with which to evaluate the similarity between terrestrial analogue sites and models of the Europan ocean and that takes into account all major variables that could determine habitability. Given the number of possible variables, classifying analogue environments is an inherently multivariate problem. Current classification systems for aqueous environments tend to fall short as they rely on human input, use inconsistent parameters or do not account for all relevant physicochemical conditions. To address this issue, machine learning models can be used, which are self-improving algorithms able to learn what a categorised dataset looks like and then make predictions on what category new data will fit into [8].

Methods

A terrestrial analogue database was constructed with published chemical (ionic composition), temperature, pressure, and pH data from potential analogue sites, including subglacial lakes, saline lakes and hydrothermal environments. Using a range of multivariate classification methods and clustering solutions, categories were defined by the full range of known physicochemical characteristics. Machine learning algorithms were trained with such categories and the highest accuracy model was selected.

New samples (such as new potential analogue sites, data from a Europan model or even direct measurements) can be fed into the trained model and it will output a so-called similarity score. This score is based on how similar the model calculates this new sample is to each of the categories of the training dataset. The category with the highest similarity score contains the sites that should be considered analogous to the new sample; in our case this new sample can be any Europan composition model found in the literature.

Cross validation methods and genetic algorithms were used to improve the models and thus the accuracy of the similarity scores. Cross-validation creates subsets of the database and assigns one to be used to evaluate the model and the rest to train it. The process then repeats by selecting a different subset to be used to evaluate the model, leaving the rest as part of the training set, until every subset has been used to both train the model and test it.  Genetic algorithms operate on the principle of biological evolution, by generating multiple versions of the model, changing certain parameters stochastically (mutation) and selecting those with the desired metrics to populate the subsequent generation of versions of the model. These processes were applied to several machine learning algorithms to select the ones with the highest accuracy.

Results

We applied the model of selecting possible analogues to existing estimates of Europa’s ocean chemistry. Initial classification (accuracy 90.6%) attempts suggest the use of low temperature sites: either sulphate-saline dominated lakes like Basque Lake (Canada) or Last Chance (Greenland) (similarity 96.0%); or calcium-rich lakes like Don Juan Pond (Antarctica) or El Chichón (Mexico) (similarity 99.9%). The similarity between the physicochemical data of the modelled Europan ocean and the terrestrial analogue sites can be calculated with high accuracy, justifying the use of microbial communities or geochemical samples from these environments for studying the habitability of extra-terrestrial environments. Ongoing work is improving the predictive accuracy of our machine learning model. The results from this work demonstrate that machine learning algorithms can improve the selection process of field sites for the study of microbial ecology and astrobiology.

References

[1] Russell et al. (2017). Astrobiology, 17(12), 1265–1273. [2] Kivelson et al. (2000). Science, 289(5483), 1340–1343. [3] Pappalardo et al.  (1999). Journal of Geophysical Research E: Planets, 104(E10), 24015–24055. [4] Jin & Ji (2012). Science China: Physics, Mechanics and Astronomy, 55(1), 156–161. [5] Trumbo et al. (2019). Science Advances, 5(6), 2–6. [6] Zolotov & Shock (2001). Journal of Geophysical Research E: Planets, 106(E12), 32815–32827. [7] Ligier et al. (2016). The Astronomical Journal, 151(6), 163. [8] Mander et al. (2013). Proceedings of the Royal Society B: Biological Sciences, 280(1770).

How to cite: del Moral, A., Pearson, V., Fox-Powell, M., and Olsson-Francis, K.: Using supervised machine learning methods to improve the selection of analogue sites for studying habitability of the sub-surface ocean of Europa, Europlanet Science Congress 2020, online, 21 Sep–9 Oct 2020, EPSC2020-474, https://doi.org/10.5194/epsc2020-474, 2020.