TP5

Introduction

Hypervelocity impact phenomena are ubiquitous throughout our Solar System and, as a result of their highly energetic nature, have been responsible for a variety of both constructive and destructive events. Through the study of hypervelocity impacts we have gained unique insight into the on-going processes experienced by bodies in space, along with the effects these processes have on different materials [1]. With the number of space missions prioritizing the detection and collection of organic signatures ever-increasing, it has become necessary to consider whether collection methods can affect the composition and integrity of organic compounds [2-5]. Here, pyrene, a polycyclic aromatic hydrocarbon, was fired onto an aluminium (Al-1100) foil using a two-stage light gas gun (LGG) at 6.39 kms^-1. Raman analyses of the foils suggest that the energy experienced on impact was sufficient to modify the pyrene into graphite. This demonstrates that sampling protocols need to be carefully considered as materials may, inadvertently, get corrupted in the collection process.

Materials & Methodology

The University of Kent’s two-stage LGG [6] was used to horizontally accelerate pyrene prior to impacting an aluminium foil at 6.39 kms^-1. The foils were then examined using a Hitachi S-4700 cold field emission Scanning Electron Microscope (FEG-SEM), followed by Raman analyses using a Horiba LabRam HR-800 spectrometer with a 633 nm laser.

Results

The results from this experiment indicate that around the rim of the crater the pyrene has been modified into graphite (Figure 1).

Figure 1: An example crater formed as a result of pyrene hitting the aluminium foil. Top: a FEG-SEM image of the crater at 3500× magnification, 5 kV. Middle: A map showing the graphite detected around the rim of the crater (red) using Raman spectroscopy. Bottom: Example Raman spectrum of one of the red dots in the maps, showing the characteristic graphite peak at 2650 cm^-1.

Additionally, the Raman data suggests that there is a different population of residues in the base of the crater that corresponds to neither pyrene nor graphite (Figure 2).

Figure 2: Raman maps of the crater showing the different residue compositions. Top: The graphite residue around the rim of the crater (red) shown with the localized residue at the base of the crater (green). Middle: The residue at the base of the crater is shown to be localized and confined within the crater floor. Bottom: Raman spectrum of the residue at the base of the crater. The peaks highlighted in green between 600-700 nm are not seen with pyrene or graphite and have not been identified, but could be the signature of an organo-metallic complex, i.e. [7].

Discussion and Conclusions

The results from this experiment show that, at 6.39 kms^-1, the energy experienced during impact is sufficient to modify pyrene into graphite, presumably by breaking the bonds between the aromatic rings. Moreover, a different population of residues is observed on the crater floor with characteristic peaks between 600-700 cm^-1. Although these residues are difficult to characterize, several hypotheses are posed. Firstly, it is suggested that the residues at the base of the crater could be disorganized pyrene resulting from the high pressures and temperatures experienced by the projectile on impact. Other possibilities include that a metal complex formed as a result of the reaction between the pyrene and aluminium foil, or perhaps the aluminium catalysed a reaction encouraging the (possibly partial) formation of benzene rings. This is due to the 680 cm^-1 line, which also closely corresponds to one of the only strong benzene peaks. Nevertheless, the results from these experiments clearly demonstrate that organic, polycyclic aromatic hydrocarbon compounds, such as pyrene, can be inadvertently modified on collection due to impact. Therefore, it is important to constrain sampling parameters, particularly velocity and collection substrate, to ensure that precious material collected in space is done so in the least compromising way. Only that way will we be able to make accurate identifications and classifications of materials which may, one day, help us uncover the secrets of our Solar System.

Acknowledgements

The authors would like to thank the UK Sciences and Technology Facilities Council (STFC) for funding and M. C. Price for all his help and advice.

References

[1] Melosh H.J.: Impact cratering: a geologic process, Oxford University Press, 1989. [2] Mathies R.A. et al (2017) Astrobiology, Vol. 17 (9):902-912. [3] New J.S. et al (2020) MAPS, Vol. 55 (3):465-479. [4] New J.S. et al (2020) MAPS, Vol. 55 (8):1936-1948. [5] Henkel T. et al (2012) 43^rd Lunar and Planetary Science Conference. [6] Burchell M.J. et al (1999) Meas. Sci. Technol., 10(41). [7] Henkel T. et al (2012) 75^th Annual Meteoritic Society Meeting.

How to cite: Spathis, V. and New, J.: Shock modification of organic compounds: investigating the effects of hypervelocity impacts of pyrene onto aluminium, Europlanet Science Congress 2021, online, 13–24 Sep 2021, EPSC2021-607, https://doi.org/10.5194/epsc2021-607, 2021.

Impacts are prevalent in the solar system and have played a profound role in the evolution of the solar system bodies. The delivery of prebiotic compounds through impact events is thought to be a crucial step in developing habitable conditions on a planetary surface. Impact events are, therefore, significant in our understanding of the origins of life on Earth or elsewhere. Previous studies have reported the role of the impact process in the abiotic synthesis of building blocks of life, such as amino acids [1-3] and peptides [4, 5]. Here, we report the results of an experimental investigation simulating hypervelocity impacts in the laboratory on an icy mixture of amino acids. Various batches of amino acid mixtures within water ice targets, mimicking the icy bodies (140 K), were prepared and a spherical bullet of size 1 mm was fired at a speed of approximately 5 km s^-1 using the light gas gun facility at the University of Kent [6]. Extremely high pressure of 10’s of gigapascals is achieved within a very short time scale as might be expected to be achieved under impact-induced shock conditions. After the impact, the ejected material from the target was collected and analyzed. When these ejecta was subjected to a Scanning Electron Microscope (SEM) analysis, it revealed ordered structures with interesting morphological features. A SEM micrograph of amino acid glutamine ejecta consisting of dendritic patterns is shown in Figure 1. LCMS analysis of ejecta residue shows that long polypeptide is synthesized as a result of impact.

Figure 1 SEM micrographs of ejecta after impact from glutamine-water ice target shows dendritic patterns with several branching structures.

The ability of shocked amino acids to form polypeptides assembled in the form of complex macroscale structures provides evidence for the evolution of the building blocks of life under impact-shock conditions. Peptides play a crucial role in the origin of life because of their unique architecture and self-assembling properties [7] and thus, prebiotic availability of peptides is believed to be crucial for the origin of life. The present results provide another step in the elucidation of our understanding of the role played by complex molecules and impact events in the origin of life. 

References

1. Bar-Nun, A., et al., Shock synthesis of amino acids in simulated primitive environments. Science, 1970. 168(3930): p. 470-472.

2. Furukawa, Y., et al., Biomolecule formation by oceanic impacts on early Earth. Nature Geoscience, 2009. 2(1): p. 62-66.

3. Martins, Z., et al., Shock synthesis of amino acids from impacting cometary and icy planet surface analogues. Nature Geoscience, 2013. 6(12): p. 1045-1049.

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

5. Sugahara, H. and K. Mimura, Glycine oligomerization up to triglycine by shock experiments simulating comet impacts. Geochemical Journal, 2014. 48(1): p. 51-62.

6. Burchell, M.J., et al., Hypervelocity impact studies using the 2 MV Van de Graaff accelerator and two-stage light gas gun of the University of Kent at Canterbury. Measurement Science and Technology, 1999. 10(1): p. 41.

7. Frenkel-Pinter, M., et al., Prebiotic Peptides: Molecular Hubs in the Origin of Life. Chemical Reviews, 2020.

How to cite: Singh, S. V., Dilip, H., Meka, J. K., Thiruvenkatam, V., Vishakantaiah, J., Muruganantham, M., Sivaprahasam, V., Sekhar, R., Bhardwaj, A., Mason, N., Burchell, M., and Sivaraman, B.: Hypervelocity impact on amino acids embedded in water ice, Europlanet Science Congress 2021, online, 13–24 Sep 2021, EPSC2021-466, https://doi.org/10.5194/epsc2021-466, 2021.

Abstract

We present laboratory activities of preparation, characterization, and UV irradiation processing of Mars soil analogues, which are key to support both in situ exploration and sample return missions devoted to detection of molecular biosignatures on Mars.

In detail we prepared analog mineral samples relevant to the landing sites of past, present and future Mars exploration missions, such as Gale Crater, Jezero Crater, and Oxia Planum. We doped these samples with a large variety of organic molecules (both biotic and prebiotic molecules) like amino acids, nucleotides, monosaccharides, aldehydes, lipids. We investigated molecular photostability under UV irradiation by monitoring in situ possible modifications of infrared spectroscopic features. These investigations provide pivotal information for ground analysis carried out by rovers on Mars.

Introduction

Laboratory simulations of Mars are key to support the scientific activity and technology development of life detection instruments on board present and upcoming rover missions such as Mars2020 Perseverance [1] and ExoMars2022 Rosalind Franklin [2]. Studies about the stability of organic molecules in a Martian-like environment allow us to explore the conditions for the preservation of molecular biosignatures and develop models for their degradation in the Martian geological record. A systematic study of the effects of UV radiation on a variety of molecule-mineral complexes mimicking Martian soil can be key for the selection of the most interesting samples to analyse in situ or/and collect for sample return. Testing the sensitivity of different techniques for detection of the diagnostic features of molecular biosignatures embedded into mineral matrices as a function of the molecular concentration helps the choice, design and operation of flight instruments, as well as the interpretation of data collected on the ground during mission operative periods.

Methods

Experimental analyses were conducted in the Astrobiology Laboratory at INAF-Astrophysical Observatory of Arcetri (Firenze, Italy). Laboratory activities pertain to: (i) synthesis of Mars soil analogues doped with organic compounds that are considered potential molecular biosignatures; (ii) UV-irradiation processing of the Mars soil analogues under Martian-like conditions; and (iii) spectroscopic characterization of the Mars soil analogues.

Results

Such studies have shown to be very informative in identifying mineral deposits most suitable for preservation of organic compounds, while highlighting the complementarity of different techniques for biomarkers detection, which is critical for ensuring the success of space missions devoted to the search for signs of life on Mars.

We will present a series of laboratory results on molecular degradation caused by UV on Mars and possible application to detection of organics by Martian rovers [3,4,5,6]. In detail, we investigated the photostability of several amino acids like glycine, alanine, methionine, valine, tryptophan, phenylalanine, glutamic acid, prebiotic molecules like urea, deoxyribose and glycolaldehyde, and biomarkers like nucleotides and phytane adsorbed on relevant Martian analogs. We monitored the degradation of these molecule-mineral complexes through in situ spectroscopic analysis, investigating the reflectance properties of the samples in the NIR/MIR spectral region. Such spectroscopic characterization of molecular alteration products provides support for two upcoming robotic missions to Mars that will employ NIR spectroscopy to look for molecular biosignatures, through the instruments SuperCam on board Mars 2020, ISEM, Ma_MISS and MicrOmega on board ExoMars 2022.

Acknowledgements

This research was supported by the Italian Space Agency (ASI) grant agreement ExoMars n. 2017-48-H.0.

References

[1] Farley K. A. et al. (2020) Space Sci. Rev. 216, 142.

[2] Vago, J. L. et al. (2017) Astrobiology 6, 309–347.

[3] Fornaro T. et al. (2013) Icarus 226, 1068–1085.

[4] Fornaro T. et al. (2018) Icarus 313, 38-60.

[5] Fornaro T. et al. (2020) Front. Astron. Space Sci. 7:539289.

[6] Poggiali G. et al. (2020) Front. Astron. Space Sci. 7:18.

How to cite: Fornaro, T., Poggiali, G., Corazzi, M. A., Garcia, C., Dimitri, G., and Brucato, J. R.: Search for molecular biosignatures on Mars: laboratory simulations of UV irradiation of molecule-mineral complexes, Europlanet Science Congress 2021, online, 13–24 Sep 2021, EPSC2021-705, https://doi.org/10.5194/epsc2021-705, 2021.

We have modeled the possible interior structures of habitable zone rocky exoplanets based on their masses and radii. In our model, the planetary interior is divided into four layers: iron core, rocky mantle, high pressure ice and water / ice. In order to assess the habitability of these planets, we have estimated the minimum and maximum H2O content of each exoplanet. We have calculated the tidal heating of the host star as well as the heat flux from the decay of radioactive elements in the interior of the planets. We have estimated whether these processes, along with the incident stellar flux, could provide sufficient energy to melt the upper ice layers and act as a continuous source of heat to sustain liquid water either inside the planet or on the planetary surface. Taking into account all these effects, we have a better understanding of the habitability of these planets. We propose to make new observations of those planets that we have found habitable to better constrain their parameters and to characterize their atmospheres.

How to cite: Boldog, Á., Dobos, V., and Barr, A. C.: Modeling the interiors of rocky exoplanets in the habitable zone, Europlanet Science Congress 2021, online, 13–24 Sep 2021, EPSC2021-474, https://doi.org/10.5194/epsc2021-474, 2021.

The Planetary Terrestrial Analogues Library (PTAL) project aimed to build and exploit a spectral database for the characterization of the mineralogical and geological evolution of terrestrial planets and small Solar System bodies. The lithological collection of PTAL consists now of 102 terrestrial rock type samples, which form the basis for the spectral library. The PTAL rock types include volcanic, igneous and sedimentary rocks and regoliths from well-studied locations all over the world. The target samples have composition comparable to what is currently known about the Martian global rock type distribution and some samples intend to shed light on the mineralogical properties of the landing area for Mars2020-Perseverance and ESA’s ExoMars (compare Bultel et al., Krzesinska et al., this conference).

The sample characterisation includes mineralogical and chemical analyses with standard commercial and dedicated spacecraft instrumentation (RAMAN, NIR, LIBS) under laboratory conditions (Veneranda et al, 2019; Lantz et al, 2020; Loizeau et al, 2020). The data base also includes detailed field description of the sample sites, coordinates, field photos, the macroscopic appearance of the rock samples and standard geological/petrographic information based on optical thin section studies and XRD (Dypvik et al., in review). 

Our collection of natural field-collected and artificial planetary analogue materials is supplemented by materials, which have been altered in laboratory experiments. These weathering experiments allowed providing spectral information on the formed mineral assemblages and we recommend reinterpretation of previous remote sensing interpretations (Viennet et al. 2017, 2019, Sætre et al. 2019, Bultel et al. 2019).

Being built on naturally occurring, terrestrial, common whole rock samples, in which minerals occur in their natural settings and relations is the biggest strength of this analogue rock collection. It allowed studying possible detection interferences and a comparison of the sensitivity of the different techniques. The collection forms the base for characterization of various alteration pathways manifested in mineralogy and geochemistry of rocks, in order to better understand and explain the alteration and weathering on Mars.

The PTAL spectral library will be made public during this conference. The main aim of the database is to provide sets of whole rock and mineral spectra of rocks that are relevant for rover and satellite missions. The spectra shall aid comparison, identification, quantification and spectral calculation when spectroscopic instruments such as NIR, RAMAN and LIBS operate in planetary missions and/or analysing materials in the field or in the laboratory. The PTAL database will allow users to jointly interpret laboratory results and newly gathered in-situ or remote sensing data using instruments (NIR, LIBS, RAMAN) on board of current and future space missions (e.g., JAXA’s Hayabusa-2, NASA’s Curiosity and Mars2020-Perseverance (Farley et al. 2020) and ESA’s ExoMars-Rosalind Franklin (Vago et al. 2017) rovers).  We will show that the careful characterisation of analogue whole rock samples change the interpretation compared to mineral separate spectra, and allow the assessment of biosignature preservation potential and the presence of organic compounds. We caution that living organisms often contaminate terrestrial rocks, but also organic signatures can be rock compounds incorporated in the rock matrix during multiphase geological processes. The latter comprise on Earth plate tectonics and mountain belt formation, and therefore even if sample spectra may resemble the spectral signature on planetary surfaces, they may not be appropriate  analogues due to their individual evolutionary pathways.   

This database features spectral tools (compare Veneranda et al., this conference) allowing for the spectral data treatment. We have implemented the integration of the database management and algorithms in an end-user platform with graphical interfaces for the use of the data and analysing tools. We will have a demonstration and tutorial (see splinter meetings) and the release of the Planetary Terrestrial Analogues Library to the public during this conference.

Acknowledgements: This project is financed through the European Research Council in the H2020-COMPET-2015 programme (grant 687302).

References: Bultel, Viennet, Poulet, Carter, Werner (2019) Journal of Geophysical Research: Planets 124 DOI: 10.1029/2018JE005845. Dypvik et al (in review) Planetary and Space Science. Farley et al. (2020) Space Sci. Rev. 216, 142. Lantz, Poulet, Loizeau, Riu, Pilorget, Carter, Dypvik, Rull, Werner (2020) Planetary and Space Science 189, 104989. Loizeau, Lequertier, Poulet, Hamm; Pilorget, Meslier-Lourit, Lantz, Werner, Rull, Bibring (2020) Planetary and Space Science 193, 105087. Sætre, Hellevang, Riu, Dypvik, Pilorget, Poulet, Werner (2019) Meteoritics & Planetary Science 1-22. Vago et al. (2017) Astrobiology 17, 471–510. Veneranda, Sáiz, Sanz‐Arranz, Manrique, Lopez‐Reyes, Medina, Dypvik, Werner, Rull (2019) Journal of Raman Spectroscopy 2019, 1–19. Viennet, Bultel, Riu, Werner (2017) Journal of Geophysical Research – Planets 122, 2328–2343. Viennet, Bultel, Werner (2019) Chemical Geology 52, 82-95.

How to cite: Werner, S. C., Poulet, F., and Rull Perez, F. and the The PTAL Project Team: PTAL – The Planetary Terrestrial Analogues Library for interpreting spectroscopic data, Europlanet Science Congress 2021, online, 13–24 Sep 2021, EPSC2021-627, https://doi.org/10.5194/epsc2021-627, 2021.

The practical limitations inherent to human and robotic planetary exploration necessitate the development of specific protocols, instrumentations and methods. This non-standard approach implies testing and validation phases in order to optimize the setups and to improve the scientific interpretations prior to, during, and after a mission. These tests are made either using space instruments or representative systems and are carried out on ‘analogue samples’ and/or in ‘analogue sites’. Analogues can be globally defined as objects or sites having compositions and/or physical properties similar to specific extraterrestrial objects.

Nevertheless, due to the variability in composition and properties of natural materials, there are always – inevitably – some differences between the analogue and the object(s) to which it refers. In studies using analogues, it is thus important to focus on the specific properties that need to be imitated and to consider analogue properties rather than analogue sites or samples alone.

Thus, we recently introduced the concept of “functional analogues” (Foucher et al., 2021).  Functional analogues are defined as terrestrial sites, materials or objects exhibiting general properties more or less similar to those anticipated on the targeted extraterrestrial body, but having specific analogue properties that are highly or perfectly relevant for a given use.

Based on this definition, we sorted functional analogues according to their utility for different domains, from engineering to astrobiology, throughout the timeline of space missions. We also proposed logical pathways to facilitate the selection of the best-suited functional analogue(s) according to their intended use.

Reference: Foucher, F., Hickman-Lewis, K., Hutzler, A., Joy, K.H., Folco, L., Bridges, J.C., Wozniakiewicz, P., Martínez-Frías, J., Debaille, V., Zolensky, M., Yano, H., Bost, N., Ferrière, L., Lee, M., Michalski, J., Schroeven-Deceuninck, H., Kminek, G., Viso, M., Russell, S., Smith, C., Zipfel, J., Westall, F., 2021. Definition and use of functional analogues in planetary exploration. Planetary and Space Science 197, 105162.

How to cite: Foucher, F., Hickman-Lewis, K., and Westall, F. and the EURO-CARES team: Definition and use of functional analogues in planetary exploration, Europlanet Science Congress 2021, online, 13–24 Sep 2021, EPSC2021-593, https://doi.org/10.5194/epsc2021-593, 2021.

There is no confirmed exomoon discovery up to date, and a possible explanation for this is the lower probability of stable moon orbits around close-in planets which are often easier to observe (Barnes & O'Brien 2002). We provide a target list for observations listing known exoplanets which might host habitable moons on stable orbits. For this, we investigate the habitability of hypothethical moons that are on stable orbits around known exoplanets. To determine their habitability, we calculate the incident stellar radiation and the tidal heat flux that might arise in moons depending on their orbital and physical parameters. Our target list contains interesting observation targets which might help in detecting the first habitable exomoon.

How to cite: Dobos, V. and Haris-Kiss, A.: A target list for observing habitable exomoons, Europlanet Science Congress 2021, online, 13–24 Sep 2021, EPSC2021-189, https://doi.org/10.5194/epsc2021-189, 2021.

The discovery of more than 4000 exoplanets in the last 25 years has rapidly established a whole new field of study: namely, that of exoplanetary sciences. The longstanding philosophical issue on the origin and the distribution of life beyond Earth has recently abandoned the realm of speculation and entered the scientific debate: for the first time in history, we do have the means to discover extraterrestrial life.

The remote detection of life is based on the fact that life uses chemical reactions to extract, store and release energy, producing by-products in its metabolic processes that, under the right conditions, can build up in the atmosphere to a detectable concentration. This is the case of Earth’s molecular oxygen (O2), the waste product of the photosynthetic activity of autotroph organisms that, without a continuous biological source, would disappear in just a few million years. Detecting oxygen in exoplanetary atmospheres has been considered for decades as a tracer of life, even if caution must be taken to definitely rule out alternative abiotic explanations: a stronger constraint would be, for instance, the concurrent detection of O2/O3 and a reduced gas like CH4 or N2O. Searching for the footprint of life in exoplanetary atmospheres will be feasible thanks to next-generation space missions like NASA’s JWST and ESA’s ARIEL and ground-based facilities like SPHERE@VLT, GPI@GEMINI and PCS@E-ELT,
retrieving the atmospheric transmission, reflection and emission spectra of extrasolar planets.

While terrestrial oxygenic photosynthesis exploits just a quite narrow window of the electromagnetic spectrum (PAR, 400-700 nm), it has been suggested that the upper limit might be pushed to 1050 nm or even 1400 nm, allowing organisms to make the most of the irradiation of the coolest M stars, too. Theoretical arguments, taking into account astrophysical, chemical, climatic and biological processes, indicate that light-harvesting processes, and in particular oxygenic photosynthesis, should be universal features of life, because they rely on an exceptionally abundant source like water and represent an effective way to harvest enormous amounts of energy, extremely prone to strong positive evolutionary selection.

Whether photosynthesis leads to oxygen buildup is another matter: oxygenation time depends sensitively on the balance between processes creating ("sources") and destroying ("sinks") oxygen, and Earth’s history reminds how a world with photosynthetic organisms does not have to be highly oxygenated.
We developed a toy model that, starting from the oxygenation history of our planet, tries to discern the key processes dictating the long-time evolution of molecular oxygen: it turns out that free O2 is a small residue of interactions involving atmosphere, lithosphere, hydrosphere and biosphere. The main oxygen sinks are volcanic and metamorphic outgassing, weathering and serpentinisation. Starting from present values of sources and sinks, analytical forms for their time evolution were searched. The biomass term was modelled through the logistic function, commonly used to describe bacterial growth, and allowing for up to four different episodes of accretion. Despite many simplifications, the model yielded a good fit to the reconstructed O2 time evolution, with four biomass bumps at t = 2.3 Gyr, t = 720 Myr, t = 370 Myr and t = 260 Myr ago, consistent to paleontological evidence.

Although the assumptions behind the model are necessarily Earth-based, an attempt was made to generalise it to exoplanets in order to get some insights on possible mechanisms preventing or enhancing the plausibility of oxygen accumulation. Geological factors, like the presence of plate tectonics and of a strong magnetic field, are highly uncertain and rely on models lacking, as we know, any observational verification; scaling relations, based on recent work, were used to model sources and sinks. As regards the biological source, building on the work by Lingam & Loeb (2019), we posit that the maximum biomass sustainable by a world is dictated by the availability of light and nutrients. In contrast to Earth, some worlds can receive too little PAR to sustain Earth-like biospheres; as a result of the decreased O2 source, they would have longer oxygenation time or even, if Fsource < Fsink, accumulate no free oxygen at all.

A clear distinction has emerged between nutrient-limited and light-limited worlds. Nutrient-limited worlds are virtually unaffected by the spectral class of their host star and follow a similar evolutionary history as the Earth. Larger planets than the Earth may take several billion years before evolving land life, perhaps posing a physical limitation to higher habitability. The effect of a  different water coverage fo is a delicate balance between varying ocean primary production and continental weathering: worlds with fo < 0:6 do not accumulate enough oxygen to develop land life. Light-limited worlds, which should be common around M stars if the PAR window were the same as Earths, never managed to overcome the critical O2 threshold for land colonisation. Nonetheless, concentrations as high as 0.65 PAL were reached in some cases, and the Mars-sized planet orbiting an M2 primary looks particularly intriguing, because the convergence of a high ocean productivity and small sinks causes a very stable and easily detectable O2 signal for over 10 Gyr.

Chimera planets, defined as those with a light-limited land NPP and a nutrient-limited ocean NPP, manage to accumulate significant amounts of oxygen, sometimes even higher than 1 PAL, even when the primary is an M6 star. These worlds might offer conditions for a high-paced biological evolution, even though their O2 reservoirs are extremely sensitive to biomass variations, possibly leading to lethal, anoxic transients.

The main result of our simulations is that biotic oxygen can indeed accumulate in a wide variety of planetary environments, including light-starving M-star systems, even if an O2-rich atmosphere is not the inevitable outcome of photosynthesis. Only if the biotic source outweights sinks, can oxygen begin to accumulate.

How to cite: Squicciarini, V., Claudi, R., and La Rocca, N.: Searching for the oxygen footprint of light-harvesting organisms, Europlanet Science Congress 2021, online, 13–24 Sep 2021, EPSC2021-763, https://doi.org/10.5194/epsc2021-763, 2021.

NASA and ESA are making plans for the next generation of space telescopes, which should be able to detect biomarkers in the atmospheres of exoplanets in the classical habitable zones around their stars (i.e., the range of separations at which water would be in liquid state on the exoplanet surface). The launch of James Space Webb Telescope is scheduled for October 2021. The main questions are related with the type of organisms producing such possible biomarkers and with the related metabolism? Will autotrophs be the base of the exoplanet ecological pyramid, as on Earth? Will they be phototroph or chemotroph? Will they be photosynthetic? Oxygenic or anoxygenic? Which will their photosynthetic pigments be? ESA’s LIFE or any other new concept for which scientific requirements have not been defined yet might be able to not only detect biomarkers, but to shed light on the actual biochemistry of exoplanet ecosystems. Therefore, investigating the potential variety of photosynthetic systems in exoplanets, either real or to be discovered, is actually very timely, as the requirements of new such telescope concepts are not set yet.

The conversion of solar energy to chemical energy through photosynthesis is considered one of the first metabolic routes on planet Earth. Although a low percentage of the solar radiation from our Sun is captured by photosynthesis, this metabolic route provides the energy to drive all the life on Earth. Cyanobacteria are thought to be the first photosynthetic microorganisms on Earth. Subsequent photosynthetic organisms acquired photosynthesis via cyanobacteria endosymbionts, that evolved into chloroplasts in plants (Tomioka & Sugiura 1983).

At the same time, photosynthesis modified the atmosphere of the early Earth by producing oxygen as a by-product. The concentration in this gas was increased in the primitive atmosphere, transforming the metabolic possibilities for the rest of organisms and, nowadays, oxygen supports the whole aerobic organisms on the planet. The only requirements that photosynthesis has are the exposure to optical radiation from the corresponding star and the availability of water and carbon dioxide (as a carbon source), making photosynthesis a putative imperative metabolism to be present in any particular radiative planetary system.

To deepen into this idea, ExoPhot aims to study the relation between photosynthetic systems on exoplanets around different types of stars (i.e. stellar spectral types) from an astrobiological and multidisciplinary point of view, by focusing on two aspects:

• Assess the photosynthetic fitness of a variety of photopigments (either real or hypothetical) as a function of star, exoplanet and atmospheric scenario.
• Delineate a range of stellar, exoplanet and atmospheric parameters for which photosynthetic activity might be feasible.

To accomplish these goals, we will use state-of-the-art planetary and stellar models to retrieve the radiation signatures at the planet surface for a wide range of exoplanet, atmosphere and host star parameters, and will carry out a quantification of the overlap (convolution) between those spectra with the absorption spectra of photosynthetic pigments, both terrestrial and hypothetical (our own developments on computer-simulated primordial pigments). Here, at the EPSC2021 conference, we present our preliminary results and future work to be developed.

Bibliography:

Tomioka, N. & Sugiura, M. The complete nucleotide sequence of a 16S ribosomal RNA gene from a blue-green alga, Anacystis nidulans. Molecular and General Genetics, 1983, 191, 46–50. https://doi.org/10.1007/BF00330888

How to cite: Fonseca-Bonilla, N., Marcos-Arenal, P., Cerdán, L., Burillo-Villalobos, M., García de la Concepción, J., López-Cayuela, M. A., Caballero, J. A., and Gómez, F.: ExoPhot: a new approach for the study of photosynthesis viability in exoplanetary systems., Europlanet Science Congress 2021, online, 13–24 Sep 2021, EPSC2021-718, https://doi.org/10.5194/epsc2021-718, 2021.

Several factors contribute to the emergence and development of life on planets. In addition to local factors (e.g. intrinsic planetary properties and host-star characteristics), planetary habitability can be influenced by the larger scale radiation environment of the Galaxy. Powerful astrophysical transient sources of high energy radiation, like Gamma Ray Bursts (GRBs) and Supernovae (SNe), can be life-threatening and potential cause of mass extinctions. A typical GRB at one kiloparsec distance from a planet with an Earth like atmosphere would destroy most of the ozone layer, expose the biota to harmful UVB radiation from the parent star, and trigger global cooling (due to the increase of the NO₂ atmospheric concentration). Indeed, the late Ordovician mass extinction event (~440 million years ago) may have been caused by a GRB. 

GRBs are approximately 10⁶ times more energetic than SNe but their rate is ~10,000 times lower. Both classes of transients share a stellar origin, either from the core collapse of very massive stars or from binaries of compact objects. The rate of both classes is higher in environments characterized by intense star formation. However, long GRBs prefer relatively low metallicity star forming sites. Moderately metal polluted regions seem to be the preferred sites for the formation of Earth-like planets potentially suited to harbour lifeforms. Therefore, the threats posed by GRBs and SNe to the emergence and development of life in the Milky Way depend in a not obvious way on the past 12 billion years of evolution of the star formation rate (Fig. 1), and relative metal pollution of the interstellar medium (Fig. 2).  On these grounds, we identify where and when, in the Galaxy, life had the best chances of success against lethal cosmic explosions.  

We model the lethal effect of GRBs and SNe by scaling their cosmic rates to the MW. GRBs and all SNe rates are proportional to the gas to stars conversion rate within galaxies. In the Galaxy the conversion of gas into stars increased over the past 12 billion years from the center towards the outskirts. Metallicity of newly born stars followed a similar inside-out evolution (Fig. 1 and 2). At different epochs, the number of lethal events as a function of the distance from the center of the Galaxy (Fig. 3) is computed by scaling the cosmic rate to the MW evolving properties (i.e. star formation and metallicity). 

In the early stages of the MW evolution (from its formation up to 6 billion years ago) the largest portion of the Galaxy out to 10 kpc from the center was unsuitable to life growth due to the high frequency of lethal events (i.e. > 30 every 500 million years).  Although the MW outskirts appear as a safer place to live (green contours in Fig.3), the low density (<0.1 pc² ) of terrestrial planets around stars of spectral type FGK and M (dashed and solid blue contours in Fig.1) makes life emergence comparatively unlikely.   

Starting around 6 Gyrs ago, owing to their energetics, long GRBs became the dominant lethal sources for life within the MW, with an increasing number of lethal events towards the Galaxy periphery (red-to-orange contours in Fig. 3). This is due to the increased conversion rate of relatively low metal polluted gas into massive stars in the outer regions of the MW. Such a global trend determined the formation of an increasingly larger, safer region of the MW centered around 3 kpc (green contours in Fig. 3) where biological complexes could possibly develop on the large population of terrestrial planets present there. 

The role of GRBs and SNe in the evolution of life within the last 500 Myrs in our Galaxy is shown in Fig. 4. Up to 2.5 kpc from the center the inhabitability of the MW is due to the high rate of short GRBs and SNe. Long GRBs make the outskirts of the Galaxy similarly unsafe, leaving a region between 2.5 and 8 kpc as the best place where biological systems had time to develop. We estimate ~1 long GRBs occurred in the last 0.5 Gyrs within a few kpc from the Sun, an event possibly associated with the late Ordovidcian mass extinction. Search for exoplanets harbouring lifeforms should have more chances of success looking in the direction of the Galactic center, within 5.5 kpc from the Sun, due to the combined effect of high density of terrestrial planets and of low occurrence of lethal transients.

How to cite: Spinelli, R., Ghirlanda, G., Haardt, F., Ghisellini, G., and Scuderi, G.: The best place and time to live in the Milky Way, Europlanet Science Congress 2021, online, 13–24 Sep 2021, EPSC2021-406, https://doi.org/10.5194/epsc2021-406, 2021.

One of the main topics of astrobiology is the study of life limits in stressful environments. This field of research has the aim to understand the physiological and biochemical effects on unprotected biological samples in extreme conditions, such as space. Moreover, these studies provide indications about organisms’ adaptive plasticity under a climate change perspective, the terrestrial geological past and future scenarios, as well as extra-terrestrial habitats as Mars surface.

The biological specimen chosen for this study was Xanthoria parietina (L.) Th. Fr. It is a widespread foliose lichen growing on bark and rocks which has a broad spectrum of tolerance to air pollutants such as NO_X and heavy metals, and resistance to UV-radiation because of the screening properties provided by the secondary metabolism product parietin. In this study we evaluated the ability of this lichen specie to survive under simulated UV space radiation in two different extreme environments i.e., in N₂ atmosphere (N₂) and in vacuum (10⁰~10^-2 Pa) (VAC).

Thalli of X. parietina were randomly collected in a remote area of Tuscany, Italy in June and July 2020. Thalli were dehydrated for 24 h at room temperature (25°C) and stored at -18°C until treatment. Three days before the treatment, thalli were allowed to recover their normal metabolic conditions in a growth chamber at 25 °C and 70 μmol m^-2 s^-1 PAR photons. Overnight, thalli were covered with a black cotton cloth and kept moistened by spraying with distilled water.

The simulated UV space radiation was produced using a Xe-enhanced UV lamp with a sun-like emission spectrum (wavelength range 185-2000 nm). The aforementioned atmospheric conditions (N₂ and VAC) were chosen to set up an extreme and dehydrating environment for the lichen. The total absorbed UV radiation dose was 1.34 MJ m^-2 for each exposed sample. During the irradiation, the IR reflectance spectrum of the lichen was monitored in situ with infrared spectroscopy to assess changes in spectral bands.

The efficiency of the photosynthetic apparatus was assessed as indicator of vitality, and was expressed in terms of chlorophyll a fluorescence (F_V/F_M) and Normalized Difference Vegetation Index (NDVI). The examination of X. parietina recovery through eco-physiological analysis revealed the capacity of this lichen species to survive in extreme conditions such as those simulated in this investigation. It has been highlighted the significant difference between treatments about the photosynthetic efficiency parameters recovery trends, finding that UV-radiation in vacuum produces more intense effects on F_V/F_M values. After 72h, UV N₂ fluorescence mean values recovered up to 93% of the starting ones, while UV VAC fluorescence recovered up to 45% of the pre-exposure values. The IR analysis revealed several spectral band changes in the fingerprint region. The most visible variation was the 5200 cm^-1 water band, disappearing in the overtone region. This analysis suggests that the disappearance of H₂O band after treatment is strictly linked to the thalli dehydration due to the atmospheric simulated conditions represented by N₂ insufflation and high vacuum application. Nevertheless, X. parietina was able to survive to UV-radiation in N₂ atmosphere and in vacuum, and for this reason it may be considered a candidate for further evaluations on its survival capacity in extreme conditions.

How to cite: Lorenz, C., Benesperi, R., Bianchi, E., Loppi, S., Papini, A., Poggiali, G., and Brucato, J. R.: Survival of Xanthoria parietina in simulated space conditions: spectroscopic analysis and vitality assessment, Europlanet Science Congress 2021, online, 13–24 Sep 2021, EPSC2021-207, https://doi.org/10.5194/epsc2021-207, 2021.

Astrobiology is an interdisciplinary science involving many different sources, and disciplines including geology. Biosignature identification on Earth is consequential and strictly linked with the definition of a solid geological context in order to recognize the present and past processes, environments, controls, and their potential to host life. In planetary settings, that can be studied only (or mostly) remotely, the comparative geological analysis with Earth potential analogue is essential.

Despite that, the importance of geology is often understated. We stress the importance of geological analyses in association and support of astrobiological investigations in the selection, understanding, and analyses of the study areas and in bridging the gap between the different observation scales on Earth and planets, also in the process of mission planning of remote and in situ missions.

Effective comparative studies are possible because of data acquired in the last decades on many planetary surfaces that allow Earth-like field geological investigations: this is especially true on Mars but increasingly important in all of the other planetary bodies, including the icy satellites.

In order for a mission to be effective, as an example, the collected samples must be representative of a larger body and reflect some specific feature of variation of it. This implies that the sample representativity is largely dependent on the accuracy of the geological observations that precede sampling. In particular, planning a sampling mission aimed at testing the astrobiological potential of a given target on a planetary surface, is based on the understanding of where to focus (depositional environment), which tools are needed (instruments), and finally to set the precise place where to sample within the selected environment with the ultimate goal to collect a significant sample and not just a stone.

Accordingly, the knowledge derived from Earth analogues represents the base to plan the exploration of planetary settings, in order to on one side select the right science target to look for fossil or present life traces and on the other side to test the proper techniques, that should be effective and at the same time low invasive/destructive to be suitable for planetary exploration.

Protocols for the sampling (i.e., collection, preservation, and treatment) and for the data analyses (i.e., facies analysis, instruments, combination of instruments) phases are needed both in the field and in the laboratory in order to identify the presence of biosignatures. Still, biosignatures in the rock record include many different organic or organically mediated structures and biochemical signals, which occurrence and evolution are controlled by the specific geological conditions. As a consequence, different types of biosignatures depend on different geological conditions and consequently necessitate different analytical approaches (e.g., Cavalazzi et al., 2019). In turn, this implies that different protocols depend on different geological conditions.

Several problems may hamper the possibility to constrain the analogy between Earth and planetary settings, the main issues being the problems of scale and of equifinality (Baker, 2014). The regional analyses to constrain the geological context on Earth and in the planetary settings occur at similar scales, but the scales of the observations and measurements even in the most favorable condition on Mars cannot exceed the meter scale, while on Earth even singe grains or crystals can be recognized and described already in the field. In addition to that, the problem of equifinality arises from similar effects that may be generated by different combinations of causative processes (Baker, 2014), which implies that single morphologies (landforms) can be rarely unequivocally interpreted from remote sensing analysis in terms of genetic origin.

To face these issues, the reconstruction of a broader geological context (landscape) is necessary as a pre-requisite to understand environments and processes of deposition (e.g., Pondrelli et al., 2008, 2011, 2015, 2019). Unraveling the vertical and lateral stratigraphic relations in order to correlate different coeval deposits, landforms, and structures, and comparing similarities and differences at all scales with different potential analogues on Earth, using the typical multiple working hypothesis approach (Baker, 2014), allows solid interpretations.

A solid reconstruction of the geological context must be carried out comparatively also on the potential Earth analogues. On Earth, the depositional environments and processes can be characterized, defining the facies, facies association, lateral transitions, and structure distribution at the outcrop scale, specifically the ones that are suitable for sampling and laboratory analyses, and ultimately understanding the controls on deposition (e.g.., Cavalazzi et al., 2019). This set of information provides fundamental elements to reconstruct the vertical and lateral facies/structures distribution in an analogue planetary setting (e.g., Pondrelli et al., 2008, 2011, 2015, 2019) and drives the sampling site selection but also the choice of more appropriate instrumentation.

This approach can provide not only a basic knowledge of the landing site/mission object area but is mandatory for a sample return mission and the selection of the right samples one can take a rock home, but not an outcrop. Thus, context geology is the first requirement to understand where the most significant sampling should be taken.

References

Baker, V. R. (2014). Terrestrial analogs, planetary geology, and the nature of geological reasoning. Planetary and Space Science, 95, 5–10.

Cavalazzi, B., Barbieri, R., Gómez, F., Capaccioni, B., Olsson-Francis, K., Pondrelli, M., et al. (2019). The Dallol Geothermal Area, Northern Afar (Ethiopia)-An Exceptional Planetary Field Analog on Earth. Astrobiology, 19(4), 553–578.

Pondrelli, M., Rossi, A., Marinangeli, L., Hauber, E., Gwinner, K., Baliva, A., & Lorenzo, S. (2008). Evolution and depositional environments of the Eberswalde fan delta, Mars. Icarus, 197(2), 429–451.

Pondrelli, M., Rossi, A., Platz, T., Ivanov, A., Marinangeli, L., & Baliva, A. (2011). Geological, geomorphological, facies and allostratigraphic maps of the Eberswalde fan delta, Planetary and Space Science, 59(11–12).

Pondrelli, M., Rossi, A. P., Deit, L. L., Gasselt, S. van, Fueten, F., Glamoclija, M., et al. (2015). Equatorial layered deposits in Arabia Terra, Mars: Facies and process variability. Geological Society of America Bulletin, 127(7/8).

Pondrelli, M., Rossi, A., Deit, L. L., Schmidt, G., Pozzobon, R., Hauber, E., & Salese, F. (2019). Groundwater Control and Process Variability on the Equatorial Layered Deposits of Kotido Crater, Mars. Journal of Geophysical Research: Planets. https://doi.org/10.1029/2018JE005656

How to cite: Pondrelli, M., Marinangeli, L., and Cavalazzi, B.: Astrobiology vs Geology investigations: good practices in the framework of planetary missions, Europlanet Science Congress 2021, online, 13–24 Sep 2021, EPSC2021-206, https://doi.org/10.5194/epsc2021-206, 2021.

In order to determine the viability of photosynthesis in exoplanetary environments in different stellar types systems, we decided to start from the study of photosynthetic systems and the pigments that compose them  and to verify their suitability in those exoplanetary environments. For this, we started from the main pigments of known photosynthesis, chlorophylls (chlorophyll a (Chla) (Figure 1) and phycocyanins as working models. We identified the need to go back to more basic pigments, with which to make the first tests to compare their spectra and their fit in the radiative systems of the different stellar types. After the first analyzes we realized that the chlorophyll systems are highly developed and we proposed the need to work with the basic molecule, porphyrin. Again, to our surprise, after successive spectroscopic analyzes once again we concluded that porphyrin were already very complex and evolved molecules. Then, we raised the need to go back in the process of molecular simplicity even further to much simpler parent molecules. In order to approach that simpler pigments we decided to theorically design the basic components which to work with. 

The conjugated central ring of the Chla molecule represented in Figure 1 (Phot0) is the part which gives the spectroscopic characteristics to the whole molecule. How is the simplest system that could also be conjugated and could be a precursor of the global molecule? We should star with the central theoretical simple macrocycle (Phot0).

Figure 1. Optimized geometry of the Chla (left) and the primeval pigment Phot0 (right) at CAM-B3LYP/def2-TZVP. Note that the highlighted methyl group of the Chla should be substituted by the phytyl group on a real system. The scheme represent an hypothetical retrosynthetic analysis of Chla starting from more simple row materials (Phot0 and acetylenes).

The general idea is taking this structure as a baseline and compare its absorbance with a known photosynthetic pigment (for instance Chla).

Figure 2. UV/Vis spectrum of Chlorophyll a in diethyl ether (blue) and computed UV/Vis spectrum of the primeval theoretical pigment Phot0 computed at (TD)CAM-B3LYP/def2TZVP (orange).

Here, at the EPSC2021, we will summarize our preliminary results on the origin and evolution of theoretical and natural pigments. Basically, we can conclude that one of our  simple theoretical pigment could act as a photosynthetic pigment by comparing its UV/Vis spectrum with that of the Chla. Thus, due to its characteristics, this pigment could be of great interest for anhydrous environments (e.g. Titan). The easiest way to be inert against water dissolution is to link the carbons to the nitrogen atoms less reactive. How could Nature have achieved this (on Earth)? – The answer is transforming them into a heterocycle, this is, a pyrrole. More results will be summarized in our EPSC presentation.

How to cite: García de la Concepción, J., Marcos-Arenal, P., Fonseca-Bonilla, N., Burillo-Villalobos, M., Cerdán, L., López-Cayuela, M. Á., Caballero, J. A., and Gómez, F.: Understanding the evolution of theoretically-based pigments based on their UV-Vis absorption spectra and its ability of being functional in different stellar systems., Europlanet Science Congress 2021, online, 13–24 Sep 2021, EPSC2021-787, https://doi.org/10.5194/epsc2021-787, 2021.