菅原 春菜

Ammonia (NH3) is a simple and essential nitrogen carrier in the universe. Its adsorption on mineral surfaces is an important step in the synthesis of nitrogenous organic molecules in extraterrestrial environments. The nitrogen isotopic ratios provide a useful tool for understanding the formation processes of N-bearing molecules. In this study, adsorption experiments were conducted using gaseous NH3 and representative clay minerals. The strongly adsorbed NH3 was 15N-enriched in a state of chemical equilibrium between the adsorption and desorption on the siliceous host surface. The nitrogen K-edge X-ray adsorption near-edge structure spectroscopy study revealed that these initial ammonia gases were chemically adsorbed as ammonium ions (NH4+) on clay minerals.

Understanding the origin of organic material on Mars is a major issue in modern planetary science. Recent robotic exploration of Martian sedimentary rocks and laboratory analyses of Martian meteorites have both reported plausible indigenous organic components. However, little is known about their origin, evolution, and preservation. Here we report that 4-billion-year-old (Ga) carbonates in Martian meteorite, Allan Hills 84001, preserve indigenous nitrogen(N)-bearing organics by developing a new technique for high-spatial resolution in situ N-chemical speciation. The organic materials were synthesized locally and/or delivered meteoritically on Mars during Noachian age. The carbonates, alteration minerals from the Martian near-surface aqueous fluid, trapped and kept the organic materials intact over long geological times. This presence of N-bearing compounds requires abiotic or possibly biotic N-fixation and ammonia storage, suggesting that early Mars had a less oxidizing environment than today. Mars has long been thought to contain organic compounds, but the origins and plausibility are debated. Here the authors employ a new technique to assess organic nitrogen compounds in a Martian meteorite, concluding that these compounds are indeed likely to originate from the Red Planet.

Phobos and Deimos occupy unique positions both scientifically and programmatically on the road to the exploration of the solar system. Japan Aerospace Exploration Agency (JAXA) plans a Phobos sample return mission (MMX: Martian Moons eXploration). The MMX spacecraft is scheduled to be launched in 2024, orbit both Phobos and Deimos (multiple flybys), and retrieve and return >10 g of Phobos regolith back to Earth in 2029. The Phobos regolith represents a mixture of endogenous Phobos building blocks and exogenous materials that contain solar system projectiles (e.g., interplanetary dust particles and coarser materials) and ejecta from Mars and Deimos. Under the condition that the representativeness of the sampling site(s) is guaranteed by remote sensing observations in the geologic context of Phobos, laboratory analysis (e.g., mineralogy, bulk composition, O-Cr-Ti isotopic systematics, and radiometric dating) of the returned sample will provide crucial information about the moon’s origin: capture of an asteroid or in-situ formation by a giant impact. If Phobos proves to be a captured object, isotopic compositions of volatile elements (e.g., D/H, 13C/12C, 15N/14N) in inorganic and organic materials will shed light on both organic-mineral-water/ice interactions in a primitive rocky body originally formed in the outer solar system and the delivery process of water and organics into the inner rocky planets.

© 2019 by The Geochemical Society of Japan. Interstellar ice is a reaction site for molecular evolution. Gaseous molecules are frozen at low temperature (~10 K) to form ice mantles and the energy supplied by UV photons and other energy sources can lead to the synthesis of complex organics. Nitrogen-containing organic molecules are of special interest because of their biomolecular importance and their anomalous stable nitrogen isotopic composition ( 15 N/ 14 N) in the interstellar dust environment. Thus, N-containing organic molecules are the keys to understanding the evolution of organic molecules and the solar system. We focused on amino acids and amines in refractory organic residues formed from ultraviolet (UV) irradiated interstellar ice analogues. We developed analytical techniques that enable the identification of the small quantities of molecules formed from the simulated interstellar ice analogues. Organic residue analysis of the UV-irradiated H 2 O-CH 3 OH-NH 3 ice showed the formation of three amines (methylamine, ethylamine and propylamine) and 11 amino acids (e.g., glycine, a-alanine, balanine, sarcosine, a-aminobutyric acid and b-aminoisobutyric acid). Furthermore, the compound-specific isotope analysis of nitrogen within the amino acids and the bulk organic film revealed that little isotopic fractionation occurred during formation in the simulated environment.

Living organisms on the Earth almost exclusively use L-amino acids for the molecular architecture of proteins. The biological occurrence of D-amino acids is rare, although their functions in various organisms are being gradually understood. A possible explanation for the origin of biomolecular homochirality is the delivery of enantioenriched molecules via extraterrestrial bodies, such as asteroids and comets on early Earth. For the asymmetric formation of amino acids and their precursor molecules in interstellar environments, the interaction with circularly polarized photons is considered to have played a potential role in causing chiral asymmetry. In this review, we summarize recent progress in the investigation of chirality transfer from chiral photons to amino acids involving the two major processes of asymmetric photolysis and asymmetric synthesis. We will discuss analytical data on cometary and meteoritic amino acids and their potential impact delivery to the early Earth. The ongoing and future ambitious space missions, Hayabusa2, OSIRIS-REx, ExoMars 2020, and MMX, are scheduled to provide new insights into the chirality of extraterrestrial organic molecules and their potential relation to the terrestrial homochirality. This article is part of a Special Issue entitled: D-Amino acids: biology in the mirror, edited by Dr. Loredano Pollegioni, Dr. Jean-Pierre Mothet and Dr. Molla Gianluca.

Adsorption is a fundamental phenomenon that occurs at various interfaces; however, the isotopic fractionation in stable isotopes associated with this process has not yet been well documented for most molecules. In this study, we conducted ammonia adsorption experiments on two silicate minerals, montmorillonite and saponite, to determine the nitrogen isotopic fractionation during the process. Ammonia adsorbed on these minerals is up to +44(parts per thousand) enriched in N-15 relative to initial ammonia. The degree of N-15 enrichment has a negative correlation with the adsorption ratio of ammonia. These enrichments are remarkably large compared to those reported in other physicochemical (e.g., evaporation) or biological (e.g., enzymatic reaction) processes. On the basis of these results, we can predict that preferential accumulation of (NH3)-N-15 occurs by adsorption on mineral surfaces, which may explain the heterogeneity of the N-15/N-14 ratio in the solar system.

We performed shock experiments simulating natural comet impacts in an attempt to examine the role that comet impacts play in peptide synthesis. In the present study, we selected a mixture of alanine (or-alanine), water ice, and silicate (forsterite) to make a starting material for the experiments. The shock experiments were conducted under cryogenic conditions (77 K), and the shock pressure range achieved in the experiments was 4.8-25.8 GPa. The results show that alanine is oligomerized into peptides up to tripeptides due to the impact shock. The synthesized peptides were racemic, indicating that there was no enantioselective synthesis of peptides from racemic amino acids due to the impact shock. We also found that the yield of linear peptides was a magnitude higher than those of cyclic diketopiperazine. Furthermore, we estimated the amount of cometary-derived peptides to the early Earth based on two models (the Lunar Crating model and the Nice model) during the Late Heavy Bombardment (LHB) using our experimental data. The estimation based on the Lunar Crating model gave 3 x 10(9) mol of dialanine, 4 x 10(7) mol of trialanine, and 3 x 10(8) mol of alanine-diketopiperazine. Those based on the Nice model, in which the main impactor of LHB is comets, gave 6 x 10(10) mol of dialanine, 1 x 10(9) mol of trialanine, and 8 x 10(9) mol of alanine-diketopiperazine. The estimated amounts were comparable to those originating from terrestrial sources (Cleaves, HJ., Aubrey, A.D., Sada, J.L. [2009]. Orig. Life Evol. Biosph. 39, 109-126). Our results indicate that comet impacts played an important role in chemical evolution as a supplier of linear peptides, which are important for further chemical evolution on the early Earth. Our study also highlights the importance of icy satellites, which were formed by comet accumulation, as prime targets for missions searching for extraterrestrial life. (C) 2015 Elsevier Inc. All rights reserved.

Survivability of amino acids at impact shock is an important factor to estimate the quantity of amino acids delivered by extraterrestrial bodies to the early Earth. In the study, we conducted shock recovery experiments of amino acids to understand the specific behaviors of amino acids by shock-induced pyrolysis during extraterrestrial impacts. Four amino acids (glycine, alanine, a-aminobutyric acid, and a-aminoisobutyric acid) that are abundant in meteorites were selected and mixed with mineral (serpentinite) powder to imitate asteroidal impacts. The shock pressure range achieved in the study was 3.2-35.3 GPa and the corresponding shock temperature range was calculated to be 420-830 K. The results show that survivability of the four amino acids declines steeply to 5-8% at 18.4 GPa and most of amino acids were decomposed at 35.3 GPa. These results mean that shock-induced pyrolysis of amino acids proceeds within an extremely short period of time (0.6-0.81.1,$) and has a reaction mechanism independent on chemical structures of amino acids. To compare with normal pyrolysis of amino acids at the atmospheric pressure, shock-induced pyrolysis of them is more rapid and dynamic reaction. The specific conditions of shock-induced pyrolysis; ultra high pressure and some special effects at a shock front (acceleration of particles and non-equilibrium phenomena) may be responsible for the specificities of the reactions. Our results provide new data for more realistic examination of extraterrestrial delivery of amino acids to the early Earth. (C) 2014 Elsevier B.V. All rights reserved.

We conducted shock experiments simulating comet impacts to assess the feasibility of peptide synthesis by such a process. We used frozen mixture of the amino acid glycine, water ice, and silicate (forsterite) as the starting material and applied impact shocks ranging from 4.8 to 26.3 GPa using a vertical propellant gun under cryogenic conditions (77 K). The results show that amino acid oligomerization up to trimers can be achieved. Further, linear peptides (dipeptide and tripeptide forms), which are important materials for the further elongation of peptide chains, were obtained in yields of one or two magnitudes greater than that of cyclic peptide form (diketopiperazine). These results contrast with those by Blank et al. (2001) for shock experiments of amino acid solutions at room temperature, which showed the synthesis of a comparable amount of diketopiperazines to that of the linear peptides. Thus, the existence of cryogenic conditions at the point of impact shock may be critical for the formation of linear peptides. Our results demonstrate that comet impacts could have supplied a significant amount of linear peptides on the early Earth and other extraterrestrial bodies.

A systematic REE + Y study of Archean (ca. 3.0 Ga) cherts from the Mount Goldsworthy greenstone belt in the northeastern Pilbara Craton, Western Australia was performed in order to understand their origin and depositional environment. Analyzed samples include microfossil-bearing black cherts from the Farrel Quartzite and a black vein chert from the underlying Warrawoona Group, and laminated to banded chert including carbonaceous chert, jaspilite and banded iron-formation from the overlying, deepening-upward Cleaverville Formation. Laminated to banded cherts from the Cleaverville Formation show a clear stratigraphic trend upsection of increasing Y/Ho and positive Eu-anomalies, with HREE-enrichment and positive La-anomalies. The data comprise a mixing array between two end-member components on a newly proposed Y/Ho-Eu-anomaly diagram. One end-member is interpreted to be Archean seawater, with a super-chondritic Y/Ho ratio (similar to 100) and a weak positive Eu-anomaly (similar to 3). The other end-member with a chondritic Y/Ho ratio and a negligible Eu-anomaly is assumed to be non-marine water such as continental run-off, ground water, or geothermal water. Black cherts containing microfossils in the Farrel Quartzite are characterized by a positive La-anomaly, HREE-enrichment, negligible to a slight positive Eu-anomaly, and a chondritic to slightly super-chondritic Y/Ho ratio. They are distinct from vein cherts with a distinct MREE-enrichment and contemporaneous hydrothermal cherts with pronounced Eu-anomaly, and plot close to the supposed non-marine end-member component on the Y/Ho-Eu-anomaly diagram. The black cherts were thus precipitated from a water mass influenced significantly by for example continental run-off, ground water and/or geothermal water, but not from high-T hydrothermal solution, increasing the credibility of microfossils contained in them. (C) 2009 Elsevier B.V. All rights reserved.