This session seeks papers on the biological, physicochemical, astrophysical, and paleontological studies of the living-matter origination problem, mechanism, conditions necessary and sufficient for living-matter origination and development on the Earth and other celestial objects; promising celestial objects for the living-matter occurrence, and other experimental, theoretical, and observational works related to the emergence and development of Life in our Solar System and beyond are welcomed.
This includes work related to theme of the Origins of Life to study interstellar chemistry, meteorites and comets chemistry as well as the chemistry of planets. A central issue in the research on the emergence of life is the paradoxical role of water in pre-biotic chemistry. Infact,on the one hand, water is essential for all known life, on the other hand it is highly destructive for key biomolecules such as nucleic and polypeptides.
A truly interdisciplinary approach is needed to delve into the core of the issue of emergence of life, because in addition to physics and chemistry it is also need to deploy a number of other sciences. We rely on contribution caming from mathematical or philosophical perspectives not only on astrobiology moreover we think that a part of the answers may lie in scientists who working on cancer research, genetics, space exploration paleontology who are not necessarily involved in this field. I argue that synthetic biology field, challenging most accepted definitions of life too, might also shed some novel and interesting perspectives on one of the most puzzling unanswered questions of science.
The session deals with three central "C's" relevant in discussions about living-matter origination and development on the Earth and other celestial objects: Concepts, Conditions and Cofactors.
All these approaches are dealing with transitions from non-living to living-matter and are integrating different technologies to shed some novel and interesting perspectives on one of the most puzzling unanswered questions of our science.
Tue, 21 Sep, 14:20–14:50
Chairpersons: Terence Kee, Frank Trixler, Rosanna del Gaudio
It is believed that some of the necessary organic molecules may have been formed in specific areas of space (namely dark molecular clouds, eg Horsehead nebula) and delivered on to the Earth during the early heavy bombardment period of its history, approximately 4.3-4.0 billion years ago. These organic molecules may have played a pivotal role in the formation of life on Earth. In addition, it is believed that life on Earth was formed within a very short geological time frame of only 200-300 million years. So, it is not unreasonable to suppose that these molecules were initially made in space which in effect could be, metaphorically speaking, a huge chemical laboratory.
The research (drawn from my own experimental astrochemistry) highlighted during this oral presentation focuses on the formation of molecules under a variety of simulated space conditions (eg different temperatures, levels of radiation energies and types of impinging radiations). There are two sorts of chemistry that take place in space, solid and gas phase, and although only 25% of the chemistry in space occurs in the solid phase, this will be the focus of my oral presentation.
How to cite: Jheeta, S.: Where were the molecules of life made?, Europlanet Science Congress 2021, online, 13–24 Sep 2021, EPSC2021-14, https://doi.org/10.5194/epsc2021-14, 2021.
Understanding the origin of life (OoL) remains one of the most challenging challenges today with many scientific questions still unanswered. The complexity of the problem of the origin of life has spawned a large number of possible evolutionary scenarios. Their number, however, can be dramatically reduced by the simultaneous consideration of various bioenergetic, physical, and geological constraints. It is a widely accepted hypothesis that life originated from inanimate matter, being somehow a synthetic product of molecular organic aggregates, and as such the result of a kind of synthetic prebiotic biology . In a multiverse perspective, supported by experimental data, I have already proposed the MuGeRo hypothesis in which both cosmic biotic “infection” and abiotic geochemistry contributing to trigger the emergence of life on Earth and beyond .
I proposed that spontaneous reactions demonstrated to occur in the environment supposed to exist in the young Earth might have provided the starting organic molecules on which peculiar component of rock (also meteorites) might have act as catalysts of molecular complexity initiating early life processes that, as has been proposed from other Authors are spontaneously and inevitable. In recent decades, the new scientific discipline of synthetic biology has set ambitious goals by pursuing the full design and manufacture of complete genetic circuits, or entire genomes, or even the whole minimal life in the laboratory. I hold that synthetic biology could also throw new and interesting perspectives on the topic of the origins of life and that, moreover, it could help challenge the most commonly accepted definitions of life, thus changing the way we might rethink life and its origins. Infact, following the bottom-up approach I reported experimental evidence that both extraterrestrial and terrestrial minerals and rocks containing iron produces the self-organizing M4 material (Fig.1 a-h) endowed of amino sugar-driven prebiotic synthetic processes supporting abiogenesis [2,3].
This is in addition to the hypothesis that early forms of life were already present in our solar system at the time of Earth formation .
Following the bottom-up approach and using the self-organized M4 material  obtained from meteorites and terrestrial rocks and minerals as a model for the emergence and early evolution of life on Earth, this work proposes an evolutionary scenario that satisfies the known constraints by proposing that life on Earth emerged, fueled by solar radiation, from non-enzymatic, photochemical and self-sustaining reactions, surviving through some form of redox chemistry.
The M4 material autopoietically self-assembled on hypersthenic chondrite or siderite and on fragments of same terrestrial rocks containing iron could have contributed to the chemical evolution of biomolecules by own catalytic activities that modify sugars and amino acids produced in the prebiotic environments.
Here I’m proposing that these non-enzymatic, self-sustaining, photochemical reactions might be a primitive examples of reaction network supporting abiogenic development of early life on Earth and/or beyond. Indeed, these non-enzymatic reactions appear efficient enough to provide the variety and abundance of biologically favorable molecules from which Darwinian selection operating at molecular level may have seeded protometabolic reaction in the pre-biotic contexts.
The aim of this work here is to present and discuss the new results of my ongoing experiments compared to those obtained in the past and more recently.
Indeed, the results that I obtained so far do not prove or exclude the possibility that M4 materials could be a kind of non-conventional form of pre-terrestrial life or earthly early life but demonstrate that they are certainly the results of reactions depending on mineral or rock (meteorites too) that might be considered prebiotic catalysis probably responsible for the emergence of a large pre-biotic pool of biologically favorable molecules.
Furthermore, I proposed that the photo-geochemical abiotic reactions could have given rise to a variety of independent biogenic events leading to a plurality of Darwinian Initial Life Forms (IDAs) from which the earliest forms of terrestrial life emerged giving rise to more than one LUCA (Last Universal Common Ancestor).
1.Longo, A. and Damer, B: Factoring origin of Life Hypotheses into the Search for Life in the Solar System and Beyond., Life, 2020, 10, 5:52,
2.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, https://doi.org/10.5194/epsc2020-167, 2020.
3.del Gaudio, R.,: Transition from Non-Living to Living Matter: filling the gap with a laboratory-based approach according to a Land-based birthplace and Iron catalysis hypotheses at the origin of life on the early Earth and beyond., Europlanet Science Congress-DPS Joint Meeting 2019, Vol. 13, EPSC-DPS2019-80-1 EPSC-DPS2019-80-1.
4. Geraci, G., del Gaudio, R., D'Argenio, B., Rendiconti Lincei, Vol. 12, pp. 51-68, 2001.
5. Geraci, G., D’Argenio, B., del Gaudio R. Patent US9328337 B2, granted, 2016.
How to cite: del Gaudio, R.: Transition from Non-living to living Matter: can integration of MuGeRo hypothesis and synthetic prebiotic biology laboratory approach shed light on the origin of Life? , Europlanet Science Congress 2021, online, 13–24 Sep 2021, EPSC2021-347, https://doi.org/10.5194/epsc2021-347, 2021.
The "water paradox" is an obstinate problem in the research on the chemical evolution towards the emergence of life. It states that although aqueous environments are essential for life, they hamper key condensation reactions such as nucleotide polymerisation. To overcome this paradox several hypotheses have been proposed, including scenarios based on alternative solvents like formamide, condensing agents like cyanamide, high temperatures of over 150 °C or wet/dry cycles in surface ponds. However, when appraising the prebiotic plausibility of such scenarios some general weaknesses appear. Besides the fact that all known life manages the water paradox without needing such proposed conditions, the principle that evolution builds on existing pathways indicates that the same physicochemical effects were probably involved in the abiotic origin of biopolymers as now being tapped by life via complex enzymes.
Here we show that abiotic temporal nanoconfinements of water can act as natural reactions vessels for prebiotic RNA formation. We present evidence for spontaneous, abiotic polymerisation of nucleotides in water. According to our results the reaction is enabled by the rise of anomalous properties of water when being temporarily confined between nanoscale separated particles of geological ubiquity within aqueous suspensions. These findings can solve the water paradox in such a way that nanofluidic effects in aqueous particle suspensions open up an abiotic route to biopolymerisation and polymer stabilisation under chemical and thermodynamic conditions which also exist within the intracellular environment of living cells. The fact that polymerase enzymes also form temporal nanoconfined water clusters inside their active site implies that the same physico-chemical effects are tapped for nucleotide condensation in water both by biochemical pathways and the reported abiotic route. This indicates that our model is consistent with evolutionary conservatism stretching back to the era of prebiotic chemical evolution. The consistency is further supported by the fact that water is not trapped by nanoconfinements within the polymerase core but can exchange with the surrounding intracellular fluid – a situation which is also prevalent in nanofluidic environments within aqueous particle suspensions. Our experimental finding that under the reported conditions an amino acid catalyses the abiotic polymerisation of nucleotides may give a hint to a nanofluidic origin of cooperation between amino acids and nucleotides evolving to the interdependent synthesis of proteins and nucleic acids in living cells.
The effect of abiotic RNA polymerisation in temporal nanoconfined water does not depend on highly specific mineral species and geological environments as watery suspensions of micro- and nanoparticles are virtually ubiquitous – they exist, for example, in the form of sediments with pore water, hydrothermal vent fluids containing precipitated inorganic and polyaromatic particles or dispersed aggregates inside water-filled cracks in the crust of the earth and possibly of icy moons in the outer solar system.
Greiner de Herrera, A., Markert, T. & Trixler, F. Temporal nanofluidic confinements induce prebiotic condensation in water. Preprint, DOI: 10.21203/rs.3.rs-163645/v3
How to cite: Greiner de Herrera, A. and Trixler, F.: Abiotic RNA Formation in Natural Nanoconfinements of Water: Overcoming the Water Paradox via a Nanofluidic Bridge Between Geochemistry and Biochemistry, Europlanet Science Congress 2021, online, 13–24 Sep 2021, EPSC2021-373, https://doi.org/10.5194/epsc2021-373, 2021.
Phosphorous, P, is a key biological element with major roles in replication, information transfer, and metabolism (Maciá, 2005). Interplanetary dust particles contain ∼0.1% P by weight, and meteoric ablation in the 1 μbar region of a planetary upper atmosphere will inject P, PO etc. into the atmosphere. These species will then undergo atmospheric processing before deposition at the surface. Orthophosphate (oxidation state +5) is the dominant form of inorganic P at the Earth’s surface; however, due to the low water solubility and reactivity of P(+5) salts, they have a poor bio-availability (Redfield, 1958). In contrast, less oxidised forms of P (particularly oxidation state +3) are far more bio-available. It has been suggested that these reduced forms of P may have originated from extra-terrestrial material that fell to Earth during the heavy bombardment period.
Previous studies have focused on the direct delivery of P to the surface in meteorites, to undergo processing through aqueous phase chemistry (Pasek, 2008). In contrast, the atmospheric chemistry of P has so far been ignored. Most of the mass of extra-terrestrial P entering a planetary atmosphere is carried by interplanetary dust particles (IPDs) with a mass of ~5 μg and a radius of ~100 μm (Carrillo-Sánchez et al., 2016). A substantial fraction of these particles ablate due to aerobraking, at heights of ~80 km on Mars, 92 km on Earth, and 115 km on Venus (Carrillo-Sánchez et al., 2020). The vaporized P atoms will then undergo chemical processing to form a variety of compounds, in which P may exist in different oxidation states due to the presence of both oxidizing and reducing agents in the upper atmospheres of the terrestrial planets. Here we present the first study of the meteoric ablation of phosphorous, and its subsequent chemical processing to form a variety of compounds including P in the biologically important P(+3) state.
The ablation of PO – relative to Ca – was studied in the Leeds Meteoric Ablation Simulator, and a new version of our Chemical Ablation Model (CABMOD) was developed to include the thermodynamics of P oxides in a molten meteoroid (Carrillo-Sánchez et al., 2020). The speciation of P in anhydrous chondritic porous Interplanetary Dust Particles was made by K-edge X-ray absorption near edge structure (XANES) spectroscopy at the Diamond Synchrotron; this work demonstrated that P mainly occurs in phosphate-like domains. An astronomical dust model which predicts the amounts of dust in the inner solar system produced by Jupiter Family comets, the asteroid belt, and Long Period comets, was then combined with CABMOD to predict the injection rate profile of P, PO and PO2 into the atmospheres of Mars, Earth and Venus - the Meteoric Input Function (Carrillo-Sánchez et al., 2020).
We then measured the kinetics of P, PO and OPO with a variety of atmospheric constituents using the laser flash photolysis/laser induced fluorescence technique (Douglas et al., 2019; Douglas et al., 2020). Electronic structure (ab initio quantum) calculations were also combined with statistical rate theory to produce an atmospheric chemistry network for phosphorus (Figure 1). This network shows the pathways from OPO to H3PO3 and H3PO4. These phosphorus-oxy acids then combine with the metal-containing molecules (e.g. NaHCO3, FeOH), also produced by meteoric ablation, to form metal phosphites and phosphates. These compounds polymerize into nm-sized meteoric smoke particles, which are transported down to the surface over several years (Dhomse et al., 2013).
This chemistry, together with the phosphorus MIF, was then put into the global chemistry-climate model WACCM. Figure 2 shows the predicted percentage of P(+3) to total P in meteoric smoke particles above 60 km, as a function of latitude and season. This study demonstrates that biologically important phosphorous acid (H3PO3) can form and then react with meteoric metal species to generate bio-available metal hydrogen phosphites. The global input of reduced P(+3) to the Earth’s surface is estimated to be around 600 kg year-1.
Figure 1. Schematic diagram of the chemistry of phosphorus in the earth’s mesosphere and lower thermosphere. The green and red arrows indicate the important pathways from OPO to H3PO3 and H3PO4, respectively.
Figure 2. Percentage of P(+3) to total P in meteoric smoke particles above 60 km, as a function of latitude and month (averaged over 3 years).
Carrillo-Sánchez, J.D., Bones, D.L., Douglas, K.M., Flynn, G.J., Wirick, S., Fegley, B., Araki, T., Kaulich, B., Plane, J.M.C., 2020. Injection of meteoric phosphorus into planetary atmospheres. Planet. Space Sci. 187, art. no. 104926.
Carrillo-Sánchez, J.D., Nesvorny, D., Pokorny, P., Janches, D., Plane, J.M.C., 2016. Sources of cosmic dust in the Earth's atmosphere. Geophys. Res. Lett. 43, 11979-11986.
Dhomse, S.S., Saunders, R.W., Tian, W., Chipperfield, M.P., Plane, J.M.C., 2013. Plutonium-238 observations as a test of modeled transport and surface deposition of meteoric smoke particles. Geophys. Res. Lett. 40, 4454-4458.
Douglas, K.M., Blitz, M.A., Mangan, T.P., Plane, J.M.C., 2019. Experimental Study of the Removal of Ground- and Excited-State Phosphorus Atoms by Atmospherically Relevant Species. J. Phys. Chem. A 123, 9469-9478.
Douglas, K.M., Blitz, M.A., Mangan, T.P., Western, C.M., Plane, J.M.C., 2020. Kinetic Study of the Reactions PO + O2 and PO2 + O3 and Spectroscopy of the PO Radical. J. Phys. Chem. A 124, 7911-7926.
Maciá, E., 2005. The role of phosphorus in chemical evolution. Chemical Society Reviews 34, 691-701.
Pasek, M.A., 2008. Rethinking early Earth phosphorus geochemistry. Proceedings of the National Academy of Sciences 105, 853-858.
Redfield, A.C., 1958. The biological control of chemical factors in the environment. American Scientist 46, 205-221.
How to cite: Plane, J., Feng, W., and Douglas, K.: Phosphorus Chemistry in Planetary Upper Atmospheres, Europlanet Science Congress 2021, online, 13–24 Sep 2021, EPSC2021-322, https://doi.org/10.5194/epsc2021-322, 2021.
Giant impacts have been suggested as promising scenarios under which reduced species important to prebiotic chemistry can form (e.g., CH4, NH3, HCN, PH3). This scenario relies on the ability of the impactor iron core to chemically reduce the planet's H2O inventory, producing significant quantities of H2 gas. Previous studies have focussed solely on the internal atmospheric chemistry of this process [1, 2]. The influence of the impact-generated melt phase on the atmospheric composition has been neglected. Further, the impactor’s iron inventory has been assumed to be fully available to reduce the atmosphere. Here, we examine the effects of these two assumptions, and hence the ability of giant impacts to produce atmospheres suitable for subsequent prebiotic chemistry.
We evolve our systems, comprised of a target and impactor, from their pre-impact states to a post-impact state prior to interactions between the melt and atmosphere (Figure 1). Impactors have a mass ratio of iron core to silicate mantle of approximately 30:70. A range of impactor masses are considered, although a typical mass of 2x1022 kg can be defined based off of Earth’s mantle excesses in highly siderophilic elements . The target has a pre-impact atmosphere of 100 bars CO2 and 2 bars N2, and a surface ocean of 1.85 Earth Oceans, considering estimates for early Earth. The target mantle oxygen fugacity is at the fayalite-magnetite-quartz buffer. As a result of the impact, the target’s initial atmosphere is eroded, its oceans are vaporised, and its surface is partially melted. The iron core of the impactor breaks up , and is either accreted by the target or escapes the system. Iron made available to the atmosphere during this accretion acts to reduce the vaporised oceans and form H2.
To calculate the silicate melt mass produced from impact, we use the iSALE shock physics code [5, and references therin]. Impact melt masses are determined and parametrised as a function of specific impact energy (Figure 2). To calculate the distribution of impactor iron, we use the GADGET2 smooth particle hydrodynamics code . The distribution of the impactor iron (between the atmosphere, the mantle, and escaping the system) is determined and parametrised as a function of impactor mass, impact velocity, and impact angle (Figure 3, see also ).
After impact processing, we evolve our system to equilibrium via melt-atmosphere interactions. We define equilibrium as when both the oxygen fugacities of the atmosphere and melt phase, and simultaneously the partial pressure of H2O in each phase, are equal. Melt-atmosphere interactions include redox chemistry in an H2-H2O-Fe2O3-FeO-Fe system, and water partitioning between the atmosphere and the melt phase.
We find that for larger impactor masses, both the inclusion of the impact-generated melt phase and the iron distribution individually act to decrease the abundance of H2 in the post-impact atmosphere. Together, their effects compound one another to produce a large decrease in H2 compared to the fiducial case without either effect. This change holds over a range of initial conditions.
We find that the greatest change is caused by the presence of the melt phase. Interactions between the atmosphere and melt phase alone (i.e., following previous models’ assumptions of all impactor iron being available to reduce the atmosphere ) can decrease the atmospheric H2 abundance by up to an order of magnitude, with greater change at greater impactor masses (Figure 4, left).
The distribution of the impactor's iron affects results in 2 ways. Firstly, some of the reducing power of the impactor is lost, either through iron being buried in regions of the mantle not able to take part in melt-atmosphere interactions (e.g., solid mantle or rapidly solidifying melt), or through iron escaping the system during breakup of the impactor. Secondly, at large impactor masses, the reduction of the atmosphere by the impactor iron leads to a mass loss from the atmosphere that decreases atmospheric pressure. The decreased system pressure then influences the oxygen fugacity of the melt phase and affects the partitioning of H2O, both of which affect the H2 abundance of the atmosphere at equilibrium. These effects can further decrease the atmospheric H2 by up to a factor of 3 (Figure 4, right).
Including equilibration between the impact-processed atmosphere and the impact-generated melt phase, as well as distribution of the impactor’s iron inventory, can decrease atmospheric H2 by up to an order of magnitude compared to the fiducial model not considering these effects. Overestimated H2 abundances can produce atmospheres suitable for subsequent formation of reduced species important for prebiotic chemistry. However, these atmospheres are also problematic for prebiotic chemistry in terms of surface temperatures and the blocking of Solar UV radiation by reduced carbon species in the atmosphere.
Atmospheres that are in equilibrium with the impact-generated melt phases below them, and that have been formed under distribution of the impactor iron inventory, are more oxidised and less massive than the fiducial case without either effect. These atmospheres are thus less likely to encounter issues surrounding surface temperature and UV blocking. Importantly, despite the decreases in H2 from the fiducial case, these atmospheres still host H2 abundances sufficient for subsequent prebiotic chemistry to take place.
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How to cite: Itcovitz, J., Rae, A., Shorttle, O., Citron, R., Stewart, S., Rimmer, P., and Sinclair, C.: How reduced can post-impact terrestrial atmospheres be?, Europlanet Science Congress 2021, online, 13–24 Sep 2021, EPSC2021-620, https://doi.org/10.5194/epsc2021-620, 2021.
How did life emerge from inanimate matter? The processes that led from complex organic molecules to the first self-replicating systems are no longer at play and we cannot easily reconstruct them because we do not have a geological record of the period when the transition from simple molecules to the very first forms of “life” have occurred. The presence of stable hydrosphere is considered as the first milestone in the timeline of the abiotic origin of life theory, with the second milestone being the massive accumulation of organic compounds necessary for the transition from organic chemistry to the biochemistry of life. But how Earth became so rich in complex organic molecules – up to the point that life spontaneously evolved from them - is still a matter of debate. At that stage, the abundance of liquid water, indeed, represents an obstacle for organic synthesis. Two theories have been suggested to solve this paradox, which are usually referred to as endogenous synthesis and exogenous synthesis scenarios . But in both cases, prebiotic molecules (that is, molecules which are simple to be formed in abiotic processes but contain the functional groups typical of biological molecules or have the capability to easily evolve into them) are formed in gaseous media. Indeed, gas-phase prebiotic molecules have been observed in the upper atmosphere of Titan, the massive moon of Saturn, as well as in the interstellar clouds and cometary comae.
The comprehension of the chemical processes that lead from simple atomic/diatomic species to prebiotic complex chemicals is an important part of the study on the origin of life. The study of these preliminary steps might seem relatively simple compared to the characterization of the other unknown phenomena that have led to the first living organisms. Nevertheless, the formation mechanisms of many of the prebiotic molecules that we observe nowadays in proto-stellar clouds or comets/meteorites or planetary atmospheres are far from being understood, while a comprehension of those processes can certainly help to set the stage for the emergence of life to occur.
For this reason, in our laboratory we have started a systematic investigation of gas-phase reactions leading to simple prebiotic molecules within the Italian National Project of Astrobiology—Life in Space—Origin, Presence, Persistence of Life in Space, from Molecules to Extremophiles .
In particular, by combining an experimental and theoretical approach, we have investigated a series of bimolecular reactions under single collision conditions. The aim is to provide detailed information on the elementary reactions which are employed in photochemical models of planetary atmosphere and cometary comae . In particular, we have investigated several reactive systems leading to the formation of nitriles (such as dicyanoacetylene) and imines (such as ethanimine), as well as reactive radicals that can further react in subsequent reactions. We have also investigated reactions involving nitrogen atoms and aromatic compounds (benzene, pyridine, toluene) to address the role of these compounds in the growth of N-containing aromatic compounds, a proxy of DNA and RNA bases. In this contribution, the main results concerning the reactions involving atomic nitrogen, N, or cyano radicals, CN, and cyanoacetylene, acrylonitrile, benzene, toluene and pyridine will be illustrated and the implications for prebiotic chemistry noted.
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 N. Balucani. Physics of Life Reviews 2020, 34–35, 136. DOI: 10.1016/j.plrev.2019.03.0061571-0645
How to cite: Balucani, N.: The chemistry of prebiotic N-containing compounds in the atmosphere of Titan and primitive Earth beyond a holistic approach, Europlanet Science Congress 2021, online, 13–24 Sep 2021, EPSC2021-779, https://doi.org/10.5194/epsc2021-779, 2021.
Energetic particles can drive the formation of prebiotic molecules in exoplanetary which are important for the origin of life. On the other hand, large energetic particle fluxes are known to be detrimental to developed life by damaging DNA. Thus, in order to understand the origin, and subsequent survival, of life on Earth it is necessary to first understand the energetic particle fluxes incident on Earth at that time. There are two types of energetic particles that are important: stellar energetic particles accelerated by their host star and Galactic cosmic rays.
I will present our recent results that model the propagation of these energetic particles through the wind of a Sun-like star during its lifetime. We find, at the time when life is thought to have begun on Earth, that Galactic cosmic ray fluxes were greatly suppressed in comparison to present-day values. However, I will show that stellar energetic particle fluxes would have been larger than present-day values. I motivate that the maximum stellar energetic particle energy increases for younger stars. This is extremely important because higher energy particles are more likely to impact the surface of a planet, in addition to its atmosphere. I will briefly discuss how we applied our model to an exoplanetary system and how this can be linked to upcoming observations.
How to cite: Rodgers-Lee, D., Taylor, A., Vidotto, A., and Downes, T.: The intensity of energetic particles at the evolving Earth, Europlanet Science Congress 2021, online, 13–24 Sep 2021, EPSC2021-628, https://doi.org/10.5194/epsc2021-628, 2021.
In the last few years many exoplanets in the habitable zone (HZ) of M-dwarfs have been discovered. The HZ is defined by the range of distances from a star in which a planet can maintain liquid water on its surface. M-dwarf stars (with effective temperatures between 2300 and 3800 K and masses <0.6 MSun ) are the most abundant stellar population in the Galaxy (~75 %) and currently the most promising targets to discover habitable worlds. Recent studies (e.g., France et al., 2013; Loyd et al., 2018) suggest that the X-ray/UV activity of M-dwarfs is very different from that of our Sun as a consequence of magnetic activity in their outer atmospheres responsible for strong X-ray/UV flares. Considering the closer distance of the HZ around M-dwarfs (~0.1 AU) compared to earlier spectral type (i.e. hotter) stars (~1 AU for our Sun), HZ exoplanets orbiting these stars may be subject to a variable and energetic environment. This has several implications for planetary habitability. For example, UV radiation can inhibit photosynthesis, induce DNA destruction, cause damage to various species of proteins and lipids (Buccino et al. 2007). On the other hand UV radiation is a fundamental ingredient for prebiotic photochemistry, especially for the synthesis of RNA, which favours the emergence of life (Ranjan et al. 2017).
I studied the X-ray/UV radiation environment of LHS 1140, one of the most interesting systems discovered up to now. The parent star, a M4.5 dwarf at ~15 pc from Earth, hosts LHS 1140b, a super-Earth-size planet in the HZ with an orbital period of ~24.7 days. Recently another planet has been discovered, LHS 1140c. Its orbital period is ~3.8 days. To characterize the X-ray/UV environment, I analyzed 38 ks of Swift data obtained within Cycle 14. Seventeen observations, distributed over three months, were performed providing simultaneous UV (uvw2 filter, 2000 Å) and X-ray (0.3-10 keV) data.
In order to study the relevance of the UV environment for habitability, abiogenesis and the atmospheric chemistry, two different UV bands have been considered: the far UV GALEX band (1344-1786 Å, FUVG) and the near UV GALEX band (1771-2831 , Å, NUVG). I measured the NUVG flux from the UVOT data and then estimated the FUVG flux, through a correlation between NUVG and FUVG that I obtained from a sample of low-mass stars in the GALEX public archive. With this sample, I could also compare the variability of the NUVG flux of LHS 1140 with the variability of other M-dwarfs (from M4 to M5 spectral type) implementing the estimate of the relative median deviation index MADrel (Miles & Shkolnik, 2017).
No significant variation of the NUVG flux of LHS 1140 is found over 3 months, and I did not observe any flare during the 38 ks on the target. LHS 1140 is in the 25th percentile of least variable M4-M5 dwarfs of the GALEX sample. Analyzing the UV flux experienced by the HZ planet LHS1140b, I found that outside the atmosphere it receives a NUV < 2% with respect to that of present-day Earth, while the FUVG flux is ~3 times higher. Thus, the FUVG /NUVG ratio reaching LHS 1140b is ~100-200 times greater than the ratio reaching Earth nowadays.
During my analysis I discovered a bright X-ray source at 11 arcsec from the present position of LHS 1140 (Fig. 1). Given the large proper motion of LHS 1140 (317.59 mas yr-1 in right ascension and -596.62 mas yr-1 in declination), it is very likely that archival estimates of LHS 1140 fluxes are contaminated by this source due to their positional coincidence. I characterized the spectrum of the contaminating X-ray source and could estimate, for the first time, the X-ray luminosity (0.1-3 keV) of LHS 1140 ~3x1026 erg s-1.
Through a visual inspection of the images available in literature I estimated a new spectral energy distribution (SED), excluding the images where LHS 1140 and the contaminant source were spatially coincident and using the optical and infrared images where the two sources are resolved. Thus, I estimated a new effective temperature for LHS 1140 of 3016 K, ~200 K lower than the previous estimates.