Extraterrestrial Environments Research Articles

Rethinking the Final Frontier: Cosmo-Logics and an Ethic of Interstellar Flourishing

In recent years a range of corporate and governmental entities have made increasingly strident moves toward the establishment of an off-Earth mining industry, often touting an imminent “gold rush in space.” For many proponents these proposals are thoroughly entangled with an even more ambitious set of possibilities for a new age of human history in space that will include the exploration and eventual colonization of extraterrestrial environments. This article takes off-Earth mining as an entry point into this complex terrain, exploring the way in which problematically homogenous notions of humanity and an open and available space are being deployed to do a kind of regulatory ethical work that simultaneously imposes and overcomes any limits to off-Earth expansion. In contrast to such an approach, this article aims to develop an ethics of interstellar flourishing grounded in an attentiveness to the consequential processes of worlding that are already linking up and remaking possibilities for everyone, both on and off-world.

On the formation of nitrogen-substituted polycyclic aromatic hydrocarbons (NPAHs) in circumstellar and interstellar environments.

The chemical evolution of extraterrestrial environments leads to the formation of polycyclic aromatic hydrocarbons (PAHs) via gas phase radical mediated aromatization reactions. We review that these de facto barrierless reactions are capable of forming prebiotic molecules such as nitrogen substituted PAHs (NPAHs), which represent the missing link between nitrogen bearing acyclic molecules and prebiotic nucleobases along with vitamins found in meteorites. Crucial routes leading to the incorporation of nitrogen atoms into the aromatic ring have been exposed. Pyridine can be formed from the reaction of abundant vinyl cyanide and its radical or via cyano radicals reacting with 1,3-butadiene. The NPAHs 1,4-dihydro(iso)quinoline and (iso)quinoline can be synthesized through reaction of pyridyl radicals with 1,3-butadiene or sequentially with two acetylene molecules, respectively. The inclusion of nitrogen into an aromatic system and their growth can fill the mechanistic gaps missing leading from acyclic nitrogen-bearing molecules via pyridine to NPAH-type molecules in the interstellar medium.

A simple and reliable anion-exchange resin method for sulfate extraction and purification suitable for multiple O- and S-isotope measurements.

The O- and S-isotope compositions of sulfates can be used as key tracers of the fate and sink of sulfate in both terrestrial and extra-terrestrial environments. However, their application remains limited in those geological systems where sulfate occurs in low concentrations. Here we present a simple and reliable method to extract, purify and concentrate sulfate from natural samples. The method allows us to take into account the separation of nitrate, which is known to be an issue in O-isotope analysis. The separation and concentration of sulfate from other anions in any aqueous solution are performed within a few hours via anion-exchange resin. The possible O- (δ18 O and Δ17 O) and S- (δ34 S, Δ33 S and Δ36 S) isotope exchanges, fractionations and/or contaminations are for the first time monitored during the whole procedure using initial O- and S-mass-dependent and mass-independent sulfate solutions. After elution in HCl, pure sulfate is fully retrieved and precipitated into BaSO4 , which is suitable for O- and S-isotopic measurements using established techniques. The analysis of retrieved barite presents no variation within 2σ uncertainties: ±0.5‰ and ±0.1‰ in O- (δ18 O, Δ17 O) and ±0.2‰, ±0.02‰ and ±0.09‰ in S- (δ34 S, Δ33 S and Δ36 S) isotope ratios, respectively. This study shows that the resin method for sulfate extraction and purification, in addition to being cheap, simple and quick, is applicable for the measurements of all O- and S-isotopic ratios in sulfates (including the Δ17 O, Δ33 S and Δ36 S values). Therefore, this method can be easily used for a high range of natural samples in which sulfate occurs in low concentration including aerosols, ice cores, sediments, volcanic deposits, (paleo)soils and rainwater, and thus it can be a key to our understanding of the sulfur cycle on Earth. Copyright © 2016 John Wiley & Sons, Ltd.

Incubating Life: Prebiotic Sources of Organics for the Origin of Life

The onset of life on Earth was preceded by prebiotic chemistry in which complex organic molecules were formed from simpler ones in the presence of energy sources. These prebiotic organics were either synthesized on Earth itself (endogenously) or synthesized extraterrestrially (exogenously) and then delivered to Earth. Organics have been detected in space and have been successfully synthesized under experimental conditions simulating both extraterrestrial environments and early Earth environments. Homochirality and enantiomeric enrichment of organic molecules, which were once considered to be biosignatures, can, in fact, be achieved abiotically. It is important to determine conditions that allow the formation of prebiotic organics and those that preserve them against degradation.

The importance of glyceraldehyde radiolysis in chemical evolution

Studies in chemical evolution are intended to demonstrate how compounds of biological importance are generated from substances that could have been found in abiotic conditions on the primitive Earth or in extraterrestrial environments. In this context, the aim of the present work was to examine the behavior of dl-glyceraldehyde in both aqueous solution and solid samples under gamma irradiation. We irradiated dl-glyceraldehyde at different doses and temperatures with a gamma source; even at low doses and temperature (77 K), free radicals were detected. Among the products formed were ethylene glycol and glycolaldehyde. Some sugar-like compounds were also detected.

Fluctuation Analysis of Redox Potential to Distinguish Microbial Fe(II) Oxidation.

We developed a novel method for distinguishing abiotic and biological iron oxidation in liquid media using oxidation-reduction (redox) potential time series data. The instrument and processing algorithm were tested by immersing the tip of a Pt electrode with an Ag-AgCl reference electrode into an active iron-oxidizing biofilm in a groundwater discharge zone, as well as in two abiotic systems: a killed sample and a chemical control from the same site. We used detrended fluctuation analysis to characterize average root mean square fluctuation behavior, which was distinct in the live system. The calculated α value scaling exponents determined by detrended fluctuation analysis were significantly different at p < 0.001. This indicates that time series of electrode response data may be used to distinguish live and abiotic chemical reaction pathways. Due to the simplicity, portability, and small size, it may be suitable for characterization of extraterrestrial environments where water has been observed, such as Mars and Europa. Key Words: Oxidation-reduction potential-Detrended fluctuation analysis-Iron-oxidizing bacteria. Astrobiology 16, 846-852.

The Astrobiology Primer v2.0.

1.1. What is astrobiology? Astrobiology is the science that seeks to understand the story of life in our universe. Astrobiology includes investigation of the conditions that are necessary for life to emerge and flourish, the origin of life, the ways that life has evolved and adapted to the wide range of environmental conditions here on Earth, the search for life beyond Earth, the habitability of extraterrestrial environments, and consideration of the future of life here on Earth and elsewhere. It therefore requires knowledge of physics, chemistry, biology, and many more specialized scientific areas including astronomy, geology, planetary science, microbiology, atmospheric science, and oceanography. However, astrobiology is more than just a collection of different disciplines. In seeking to understand the full story of life in the Universe in a holistic way, astrobiology asks questions that transcend all these individual scientific subjects. Astrobiological research potentially has much broader consequences than simply scientific discovery, as it includes questions that have been of great interest to human beings for millennia (e.g., are we alone?) and raises issues that could affect the way the human race views and conducts itself as a species (e.g., what are our ethical responsibilities to any life discovered beyond Earth?).

Introduction to this special section: Advances in seismic sensors

Seismic detectors have been around for centuries and seismic prospecting for many decades. The variety of seismic sensors in modern surveys is dazzling; they can measure particle velocity and acceleration, pressure and pressure gradient, strain and strain rate, and multiple components (Z, H1, H2, yaw, pitch, roll), from near DC to hundreds or thousands of hertz, in land, marine, borehole, and extraterrestrial environments.

Venturing into new realms? Microorganisms in space.

One of the biggest challenges of science is the determination of whether extraterrestrial life exists. Although potential habitable areas might be available for complex life, it is more likely that microbial life could exist in space. Many extremotolerant and extremophilic microbes have been found to be able to withstand numerous, combined environmental factors, such as high or low temperatures and pressures, high-salt conditions, high doses of radiation, desiccation or nutrient limitations. They may even survive the transit from one planet to another. Terrestrial Mars-analogue sites are one focus of researchers, in order to understand the microbial diversity in preparation for upcoming space missions aimed at the detection of life. However, such missions could also pose a risk with respect to contamination of the extraterrestrial environment by accidentally transferred terrestrial microorganisms. Closer to the Earth, the International Space Station is the most enclosed habitat, where humans work and live-and with them numerous microorganisms. It is still unknown how microbes adapt to this environment, possibly even creating a risk for the crew. Information on the microbiology of the ISS will have an impact on the planning and implementation of long-term human spaceflights in order to ensure a safe, stable and balanced microbiome on board.

Controls on the stable isotope compositions of travertine from hyperalkaline springs in Oman: Insights from clumped isotope measurements

Carbonate formation at hyperalkaline springs is typical of serpentinization in peridotite massifs worldwide. These travertines have long been known to exhibit large variations in their carbon and oxygen isotope compositions, extending from apparent equilibrium values to highly depleted values. However, the exact causes of these variations are not well constrained. We analyzed a suite of well-characterized fresh carbonate precipitates and travertines associated with hyperalkaline springs in the peridotite section of the Samail ophiolite, Sultanate of Oman, and found their clumped isotope compositions vary systematically with formation environments. Based on these findings, we identified four main processes controlling the stable isotope compositions of these carbonates. These include hydroxylation of CO2, partial isotope equilibration of dissolved inorganic carbon, mixing between isotopically distinct carbonate end-members, and post-depositional recrystallization. Most notably, in fresh crystalline films on the surface of hyperalkaline springs and in some fresh carbonate precipitates from the bottom of hyperalkaline pools, we observed large enrichments in Δ47 (up to ∼0.2‰ above expected equilibrium values) which accompany depletions in δ18O and δ13C, yielding about 0.01‰ increase in Δ47 and 1.1‰ decrease in δ13C for every 1‰ decrease in δ18O, relative to expected equilibrium values. This disequilibrium trend, also reflected in preserved travertines ranging in age from modern to ∼40,000years old, is interpreted to arise mainly from the isotope effects associated with the hydroxylation of CO2 in high-pH fluids and agrees with our first-order theoretical estimation. In addition, in some fresh carbonate precipitates from the bottom of hyperalkaline pools and in subsamples of one preserved travertine terrace, we observed additional enrichments in Δ47 at intermediate δ13C and δ18O, consistent with mixing between isotopically distinct carbonate end-members. Our results suggest that carbonate clumped isotope analysis can be a valuable tool for identifying and distinguishing processes not readily apparent from the carbonate bulk stable isotope compositions alone, e.g., kinetic effects or mixing of different carbonate end-members, which can significantly alter both the apparent formation temperatures and apparent radiocarbon ages. The isotope trends observed in these travertine samples could be applied more broadly to identify extinct hyperalkaline springs in terrestrial and extraterrestrial environments, to better constrain the formation conditions and post-depositional alteration of hyperalkaline spring carbonates, and to extract potential paleoclimate information.

Reactions of substituted benzene anions with N and O atoms: Chemistry in Titan's upper atmosphere and the interstellar medium.

The likely existence of aromatic anions in many important extraterrestrial environments, from the atmosphere of Titan to the interstellar medium (ISM), is attracting increasing attention. Nitrogen and oxygen atoms are also widely observed in the ISM and in the ionospheres of planets and moons. In the current work, we extend previous studies to explore the reactivity of prototypical aromatic anions (deprotonated toluene, aniline, and phenol) with N and O atoms both experimentally and computationally. The benzyl and anilinide anions both exhibit slow associative electron detachment (AED) processes with N atom, and moderate reactivity with O atom in which AED dominates but ionic products are also formed. The reactivity of phenoxide is dramatically different; there is no measurable reaction with N atom, and the moderate reactivity with O atom produces almost exclusively ionic products. The reaction mechanisms are studied theoretically by employing density functional theory calculations, and spin conversion is found to be critical for understanding some product distributions. This work provides insight into the rich gas-phase chemistry of aromatic ion-atom reactions and their relevance to ionospheric and interstellar chemistry.

Pilot for Validation of Online Pretreatments for Analyses of Organics by Gas Chromatography-Mass Spectrometry: Application to Space Research.

The search for complex organic molecules in extraterrestrial environments, including important biomolecules such as amino and fatty acids, will require a space compatible sample handling system to enable their detection by gas chromatography-mass spectrometry (GC-MS). For the future Mars exploratory mission Exomars 2018 aimed at organic molecules detection, a dedicated laboratory pilot, called Device for Pretreatment of Sample (DPS), reproducing representative space operating conditions has been developed. After its optimization, it aimed at validating under development protocols and interpreting forthcoming in situ resulting data. The DPS, dedicated to organic compounds' analysis, is discussed in terms of its technical features. The derivatization is carried out on a 50-100 mg mineral sample in a 4 mL reactor coupled with a GC-MS injector to simulate on line in situ derivatization-volatilization-transfer steps. Three derivatization reactions have been carried out with N-methyl-N-(tert-butyldimethylsilyl)-trifluoroacetamide (MTBSTFA) as silylating reagent, N,N-dimethylformamide dimethylacetal (DMF-DMA) and tetramethylammonium hydroxide (TMAH) as methylating agents. The performances are illustrated by comparison of conventional and in situ silylation, developed for space research applications, using terrestrial mineral matrix and Mars analog materials enriched with 25 nmol of each targeted organic molecule. The work presented in this rationale has established that the use of derivatization reactions widens the scope of targeted molecules but also clearly points out mineral matrix effect. Decreasing mineral influence on pretreatment will be the next scientific challenge in in situ analysis.

Raman spectra of Martian glass analogues: A tool to approximate their chemical composition.

Raman spectrometers will form a key component of the analytical suite of future planetary rovers intended to investigate geological processes on Mars. In order to expand the applicability of these spectrometers and use them as analytical tools for the investigation of silicate glasses, a database correlating Raman spectra to glass composition is crucial. Here we investigate the effect of the chemical composition of reduced silicate glasses on their Raman spectra. A range of compositions was generated in a diffusion experiment between two distinct, iron‐rich end‐members (a basalt and a peralkaline rhyolite), which are representative of the anticipated compositions of Martian rocks. Our results show that for silica‐poor (depolymerized) compositions the band intensity increases dramatically in the regions between 550–780 cm−1 and 820–980 cm−1. On the other hand, Raman spectra regions between 250–550 cm−1 and 1000–1250 cm−1 are well developed in silica‐rich (highly polymerized) systems. Further, spectral intensity increases at ~965 cm−1 related to the high iron content of these glasses (~7–17 wt % of FeOtot). Based on the acquired Raman spectra and an ideal mixing equation between the two end‐members we present an empirical parameterization that enables the estimation of the chemical compositions of silicate glasses within this range. The model is validated using external samples for which chemical composition and Raman spectra were characterized independently. Applications of this model range from microanalysis of dry and hydrous silicate glasses (e.g., melt inclusions) to in situ field investigations and studies under extreme conditions such as extraterrestrial (i.e., Mars) and submarine volcanic environments.

Candidate microbial ichnofossils in continental basaltic tuffs of central Oregon, USA: Expanding the record of endolithic microborings

The presence of potential microbial trace fossils (endolithic microborings) has been well documented in oceanic basaltic pillow lavas, hyaloclastites, tuffs, and transitional subglacial marine lavas in the past 30 yr. Despite their evident abundance in oceanic to subglacial environments, they have not been observed in continental basalts that were not erupted in marine or subglacial settings. To expand the record of putative endolithic microborings in volcanic rocks to nonmarine, continental lacustrine environments, we examined hydrovolcanic pyroclastic deposits in the Fort Rock volcanic field, central Oregon. This study presents the textures, mineralogy, and geochemistry of basaltic tuffs containing possible endolithic microborings comparable in morphology, size, and distribution to those described in earlier oceanic and subglacial basalt studies. We observed a variety of tubular and granular textures that show evidence of biogenic morphologies and behavior, and a primary geological context that expresses their age and syngenicity. Petrographic relationships with secondary phases (chabazite, nontronite, calcite) indicate that the construction of microtunnels occurred in saline, alkaline fluids at temperatures of 25–80 °C. In addition, positive correlations were observed between the extent of aqueous (abiotic) alteration and both the abundance of microtunnels and morphological type. These correlations suggest that microtunnels were more readily formed where there was greater abiotic alteration-fluid flux and that the resulting change in chemical composition of those fluids may have had a direct influence on the formation process or possibly the type of constructing microbe. This work adds to understanding of factors controlling microtunnel formation and is the first account of putative endolithic microborings in a continental lacustrine setting. This new information may also have implications in the search for habitable extraterrestrial environments, such as on Mars.

Mechanisms for the formation of thymine under astrophysical conditions and implications for the origin of life.

Nucleobases are the carriers of the genetic information in ribonucleic acid and deoxyribonucleic acid (DNA) for all life on Earth. Their presence in meteorites clearly indicates that compounds of biological importance can form via non-biological processes in extraterrestrial environments. Recent experimental studies have shown that the pyrimidine-based nucleobases uracil and cytosine can be easily formed from the ultraviolet irradiation of pyrimidine in H2O-rich ice mixtures that simulate astrophysical processes. In contrast, thymine, which is found only in DNA, is more difficult to form under the same experimental conditions, as its formation usually requires a higher photon dose. Earlier quantum chemical studies confirmed that the reaction pathways were favorable provided that several H2O molecules surrounded the reactants. However, the present quantum chemical study shows that the formation of thymine is limited because of the inefficiency of the methylation of pyrimidine and its oxidized derivatives in an H2O ice, as supported by the laboratory studies. Our results constrain the formation of thymine in astrophysical environments and thus the inventory of organic molecules delivered to the early Earth and have implications for the role of thymine and DNA in the origin of life.

BIOMEX Experiment: Ultrastructural Alterations, Molecular Damage and Survival of the Fungus Cryomyces antarcticus after the Experiment Verification Tests.

The search for traces of extinct or extant life in extraterrestrial environments is one of the main goals for astrobiologists; due to their ability to withstand stress producing conditions, extremophiles are perfect candidates for astrobiological studies. The BIOMEX project aims to test the ability of biomolecules and cell components to preserve their stability under space and Mars-like conditions, while at the same time investigating the survival capability of microorganisms. The experiment has been launched into space and is being exposed on the EXPOSE-R2 payload, outside of the International Space Station (ISS) over a time-span of 1.5years. Along with a number of other extremophilic microorganisms, the Antarctic cryptoendolithic black fungus Cryomyces antarcticus CCFEE 515 has been included in the experiment. Before launch, dried colonies grown on Lunar and Martian regolith analogues were exposed to vacuum, irradiation and temperature cycles in ground based experiments (EVT1 and EVT2). Cultural and molecular tests revealed that the fungus survived on rock analogues under space and simulated Martian conditions, showing only slight ultra-structural and molecular damage.

Models for the estimation of Fe3+/Fetotratio in terrestrial and extraterrestrial alkali- and iron-rich silicate glasses using Raman spectroscopyk

To develop Raman spectroscopy as a quantitative tool in both geosciences and planetary sciences the effect of iron oxidation state (Fe 3+ /Fe tot ) on the Raman spectra of basaltic and pantelleritic glasses has been investigated. We have used remelted pantellerite from Pantelleria Island and synthetic iron-rich basaltic glasses [from Chevrel et al. (2014)]. The Raman spectra of pantelleritic glasses reveal dramatic changes in the high wavelength region of the spectrum (800–1200 cm −1 ) as iron oxidation state changes. In particular the 970 cm −1 band intensity increases with increasing oxidation state of the glass (Fe 3+ /Fe tot ratio from 0.24 to 0.83). In contrast, Raman spectra of the basaltic glasses do not show the same oxidation state sensitivity (Fe 3+ /Fe tot ratio from 0.15 to 0.79). A shift, however, of the 950 cm −1 band to high wavenumber with decreasing iron oxidation state can be observed. We present here two empirical parameterizations (for silica- and alkali-rich pantelleritic glasses and for iron-rich basaltic glasses) to enable estimation of the iron oxidation state of both anhydrous and hydrous silicate glasses (up to 2.4 wt% H 2 O). The validation of the models derived from these parameterizations have been obtained using the independent characterization of these melt samples plus a series of external samples via wet chemistry. The “pantelleritic” model can be applied within SiO 2 , FeO, and alkali content ranges of ~69–75, ~7–9, and ~8–11 wt%, respectively. The “basaltic” model is valid within SiO 2 , FeO, and alkali content ranges of ~42–54, ~10–22, and ~3–6 wt%, respectively. The results of this study contribute to the expansion of the compositionally dependent database previously presented by Di Genova et al. (2015) for Raman spectra of complex silicate glasses. The applications of these models range from microanalysis of silicate glasses (e.g., melt inclusions) to handheld in situ terrestrial field investigations and studies under extreme conditions such as extraterrestrial (i.e., Mars), volcanic, and submarine environments.

Geo- and biogeochemical processes in a heliothermal hypersaline lake

Water chemical variations were investigated over three annual hydrologic cycles in hypersaline, heliothermal, meromictic Hot Lake in north-central Washington State, USA. The lake contains diverse biota with dramatic zonation related to salinity and redox state. Water samples were collected at 10-cm depth intervals through the shallow lake (2.4m) during 2012–2014, with comprehensive monitoring performed in 2013. Inorganic salt species, dissolved carbon forms (DOC, DIC), oxygen, sulfide, and methane were analyzed in lake water samples. Depth sonde measurements of pH and temperature were also performed to track their seasonal variations. A bathymetric survey of the lake was conducted to enable lake water volume and solute inventory calculations. Sediment cores were collected at low water and analyzed by X-ray diffraction to investigate sediment mineralogy.The primary dissolved salt in Hot Lake water was Mg2+-SO42− whereas sediments were dominated by gypsum (CaSO4·2H2O). Lake water concentrations increased with depth, reaching saturation with epsomite (MgSO4·7H2O) that was exposed at lake bottom. At maximum volume in spring, Hot Lake exhibited a relatively dilute mixolimnion; a lower saline metalimnion with stratified oxygenic and anoxygenic photosynthetic microbiological communities; and a stable, hypersaline monimolimnion, separated from above layers by a chemocline, containing high levels of sulfide and methane. The thickness of the mixolimnion regulates a heliothermal effect that creates temperatures in excess of 60°C in the underlying metalimnion and monimolimnion. The mixolimnion was dynamic in volume and actively mixed. It displayed large pH variations, in-situ calcium carbonate precipitation, and large evaporative volume losses. The depletion of this layer by fall allowed deeper mixing into the metalimnion, more rapid heat exchange, and lower winter lake temperatures. Solubility calculations indicate seasonal biogenic and thermogenic aragonite precipitation in the mixolimnion and metalimnion, but the absence of calcareous sediments at depth suggests dissolution and recycling during winter months. Dissolved carbon concentrations [dissolved organic carbon (DOC) and dissolved inorganic carbon (DIC)] increased with depth, reaching ∼0.04mol/L at the metalimnion–monimolimnion boundary. DIC concentrations were seasonally variable in the mixolimnion and metalimnion, and were influenced by calcium carbonate precipitation. DOC concentrations mimicked those of conservative salts (e.g., Na+-Cl−) in the mixolimnion and metalimnion, but decreased in the monimolimnion where mass loss by anaerobic microbial processes is implied. Biogenic reduced solutes originating in monimolimnion (H2S and CH4) were biologically oxidized in the metalimnion as they were not observed in more shallow lake waters. Multi-year solute inventory calculations indicated that Hot Lake is a stable, albeit seasonally and annually dynamic feature, with inorganic solutes cycled between lake waters and sediments depending on annual recharge, temperature, and lake water dilution state. With its extreme geochemical and thermal regime, Hot Lake functions as analog of early earth and extraterrestrial life environments.

Raman spectroscopy: Caution when interpreting organic carbon from oxidising environments

Oxidation on Mars is primarily caused by the high influx of cosmic and solar radiation which interacts with the Martian surface. The evidence of this can be seen in the ubiquitous red colouration of the Martian sediment. This radiation will destroy most signals of life in the top few metres of the Martian surface. If organic carbon (one of the building blocks of life) is present within the accessible Martian sediments, it is very likely that it will have experienced some oxidation. ESA׳s ExoMars mission set to fly in 2018, has on board a miniaturised Raman spectrometer. As Raman spectroscopy is sensitive to carbonaceous material and will be primarily used to characterise organics, it is essential that the effect oxidation has on the Raman carbon signal is assessed. Oxidised carbonaceous shales were analysed using Raman spectroscopy to assess this issue. Results show that haematite has a band which occurs in the same frequency as the carbon D band, which cannot be distinguished from each other. This can lead to a misidentification of the carbon D band and a misinterpretation of the carbon order. Consequently, caution must be taken when applying Raman spectroscopy for organic carbon analysis in oxidised terrestrial and extraterrestrial environments, including on Mars.

LOW TEMPERATURE FORMATION OF NITROGEN-SUBSTITUTED POLYCYCLIC AROMATIC HYDROCARBONS (PANHs)—BARRIERLESS ROUTES TO DIHYDRO(iso)QUINOLINES

Meteorites contain bio-relevant molecules such as vitamins and nucleobases, which consist of aromatic structures with embedded nitrogen atoms. Questions remain over the chemical mechanisms responsible for the formation of nitrogen-substituted polycyclic aromatic hydrocarbons (PANHs) in extraterrestrial environments. By exploiting single collision conditions, we show that a radical mediated bimolecular collision between pyridyl radicals and 1,3-butadiene in the gas phase forms nitrogen-substituted polycyclic aromatic hydrocarbons (PANHs) 1,4-dihydroquinoline and to a minor amount 1,4-dihydroisoquinoline. The reaction proceeds through the formation of a van der Waals complex, which circumnavigates the entrance barrier implying it can operate at very low kinetic energy and therefore at low temperatures of 10 K as present in cold molecular clouds such as TMC-1. The discovery of facile de facto barrierless exoergic reaction mechanisms leading to PANH formation could play an important role in providing a population of aromatic structures upon which further photo-processing of ice condensates could occur to form nucleobases.