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.

Abstract Japan Aerospace Exploration Agency's Martian Moons eXploration (MMX) mission will launch a spacecraft in 2024 to return samples from Phobos in 2029. Curatorial work for the returned Phobos samples is critical for the sample allocation without degrading the sample integrity and subsequent sample analysis that will provide new constraints on the origin of Phobos and the evolution of the circum‐Mars environment. The Sample Analysis Working Team of the MMX is designing the sample curation protocol. The curation protocol consists of three phases: (1) quick analysis (extraction and mass spectrometry for gases), (2) pre‐basic characterization (bulk‐scale observation), and (3) basic characterization (grain‐by‐grain observation and allocation of the sample aliquots). Nondestructive analyses within the clean chamber (e.g., visible and near‐infrared spectral imaging) and outside the chamber (e.g., gas mass spectrometry) are incorporated into the curation flow in coordination with the MMX mission instrument teams for ground‐truthing the remote‐sensing data sets. The MMX curation/sample analysis flow enables the seamless integration between the sample and remote‐sensing data sets to maximize the scientific value of the collected Phobos samples.

Polycyclic aromatic hydrocarbons (PAHs) contain ≲20% of the carbon in the interstellar medium. They are potentially produced in circumstellar environments (at temperatures ≳1000 kelvin), by reactions within cold (~10 kelvin) interstellar clouds, or by processing of carbon-rich dust grains. We report isotopic properties of PAHs extracted from samples of the asteroid Ryugu and the meteorite Murchison. The doubly-13C substituted compositions (Δ2×13C values) of the PAHs naphthalene, fluoranthene, and pyrene are 9 to 51‰ higher than values expected for a stochastic distribution of isotopes. The Δ2×13C values are higher than expected if the PAHs formed in a circumstellar environment, but consistent with formation in the interstellar medium. By contrast, the PAHs phenanthrene and anthracene in Ryugu samples have Δ2×13C values consistent with formation by higher-temperature reactions.

Abstract The sample from the near-Earth carbonaceous asteroid (162173) Ryugu is analyzed in the context of carbonaceous meteorites soluble organic matter. The analysis of soluble molecules of samples collected by the Hayabusa2 spacecraft shines light on an extremely high molecular diversity on the C-type asteroid. Sequential solvent extracts of increasing polarity of Ryugu samples are analyzed using mass spectrometry with complementary ionization methods and structural information confirmed by nuclear magnetic resonance spectroscopy. Here we show a continuum in the molecular size and polarity, and no organomagnesium molecules are detected, reflecting a low temperature and water-rich environment on the parent body approving earlier mineralogical and chemical data. High abundance of sulfidic and nitrogen rich compounds as well as high abundance of ammonium ions confirm the water processing. Polycyclic aromatic hydrocarbons are also detected in a structural continuum of carbon saturations and oxidations, implying multiple origins of the observed organic complexity, thus involving generic processes such as earlier carbonization and serpentinization with successive low temperature aqueous alteration.

Abstract Samples from the carbonaceous asteroid (162173) Ryugu provide information on the chemical evolution of organic molecules in the early solar system. Here we show the element partitioning of the major component ions by sequential extractions of salts, carbonates, and phyllosilicate-bearing fractions to reveal primordial brine composition of the primitive asteroid. Sodium is the dominant electrolyte of the salt fraction extract. Anions and NH₄⁺ are more abundant in the salt fraction than in the carbonate and phyllosilicate fractions, with molar concentrations in the order SO₄²⁻> Cl⁻> S₂O₃²⁻> NO₃⁻> NH₄⁺. The salt fraction extracts contain anionic soluble sulfur-bearing species such as S_n-polythionic acids (n < 6), C_n-alkylsulfonates, alkylthiosulfonates, hydroxyalkylsulfonates, and hydroxyalkylthiosulfonates (n < 7). The sulfur-bearing soluble compounds may have driven the molecular evolution of prebiotic organic material transforming simple organic molecules into hydrophilic, amphiphilic, and refractory S allotropes.

Martian Moons eXploration (MMX) is a mission under development in JAXA in cooperation with NASA, CNES, ESA, DLR to be launched in 2024. This paper introduces the result of its preliminary design and the latest status of the MMX program, putting more weight on the novel part of the mission. The goal of MMX is to reveal the origin of the Martian moons and then to make progress in our understanding of planetary system formation and of primordial material transport around the border between the inner- and the outer part of the early solar system. Additionally, the mission is to survey two Martian moons and return samples from Phobos. Add to those MMX's contribution to the planetary science field, on the growing discussion on the International Space Exploration activities, MMX's contribution to future human Mars exploration is also considered as an essential aspect of the program. Following the system definition study results presented in the previous conference, the following items will be reported in this paper. First, as a result of the comprehensive completion of the Phase-B activities, the preliminary design is completed in coordination with the design of the spacecraft system, mission instruments, and operation plans. This paper describes the proximity and surface operations around Phobos in detail. Second, Phase-C activities have started, incorporating engineering models manufacturing and tests. Those of critical technologies for surface exploration are described in detail. Moreover third, the programmatic aspects, including international cooperation frameworks and the program schedule, are presented.

Abstract We performed in-situ analysis on a ~1 mm-sized Ryugu grain A0080 returned by the Hayabusa2 spacecraft to investigate the relationship of soluble organic matter (SOM) to minerals. The DESI-HRMS (desorption electrospray ionization-high resolution mass spectrometry) imaging using methanol spray identified more than 200 soluble organic compounds, which were assigned as CHN, CHO, CHO-Na (sodium adducted), and CHNO in molecular composition. Heterogeneous spatial distribution was observed for different compound classes of SOM as well as among the same alkylated homologues on the sample surface. The A0080 sample showed similar mineralogy to that of CI chondrite and contained two different lithologies, which are rich in magnetite, pyrrhotite, and dolomite (lithology 1) and poor in those minerals (lithology 2). CHN compounds were relatively concentrated in lithology 1 than in lithology 2, on the other hand, CHO, CHO-Na, and CHNO compounds were distributed in both lithologies. Such different spatial distribution of SOM is the result of interaction of the SOM with minerals, during precipitation of the SOM via fluid activity, or could be due to difference in transportation efficiencies of SOMs in aqueous fluid. However, organic-related ions measured by ToF-SIMS did not coincide with the spatial distribution revealed by DESI-HRMS imaging, indicating that the ToF-SIMS data would be mainly derived from methanol-insoluble organic matter in A0080. Alkylated homologues of CHN compounds with large C number appeared more abundant in lithology 2 than lithology 1. In contrast, fragments of the Murchison meteorite showed different features to of A0080, implying different formation or growth mechanisms for the alkylated CHN compounds by interaction with fluid and minerals on Murchison parent body and asteroid Ryugu. This difference might be mainly attributed to the carbonate grains, which would have played as a catalyst for CH₂ growth of CHN compounds. Future in-situ analysis of CI chondrite will provide more reliable constraints for the history of soluble organic compounds in asteroid Ryugu.

For on-site analysis of surface materials on the Moon, planets, and small bodies and for the monitoring of air quality in crewed spacecraft, we have developed a portable gas chromatograph (GC) equipped with a ball surface acoustic wave (SAW) sensor. In this study, we fabricated a 10 cm cube GC that implements the forward flush method using two metal micro-electro-mechanical-system columns coated with different stationary phases in microchannels fabricated by wet etching and diffusion bonding of stainless-steel plates. Using this GC, we succeeded in analyzing 10 kinds of gas within 10 min. In addition, for the application of the ball SAW GC on the ground, we also developed a palm-sized GC with a single metal capillary column and used it in the analysis of the headspace gas of sake. We showed that the ratio of peak areas differed among odorants depending on the brand and brewing process of sake.

2020年12月6日に小惑星探査機「はやぶさ2」はC型小惑星リュウグウ表層物質を収めた再突入カ プセルを地球に帰還させた．回収された再突入カプセルに収められた試料コンテナは，オーストラリア現地でのガス採取を実施した後，JAXA相模原キャンパスの惑星物質試料受入設備に搬入され，チェンバー導入前の部品取り外し・洗浄等のプロセスを経てクリーンチェンバー内で真空中での開封・高純度窒素環境下での帰還試料の取り出し･初期記載が行われた．これらのリュウグウ帰還試料の初期記載の結果，これまでに回収されたどの隕石よりも反射率が低く，全体密度が小さい事が判明した．また，赤外反射スペクトルの吸収特性から水酸基を含む含水鉱物と炭酸塩鉱物，及びCH結合に富む有機物が試料中に含まれることが明らかになった．これらの情報を既知の隕石と比較すると，CIコンドライト隕石に最も似ていると言える．また探査機搭載機器によって得られた可視･近赤外スペクトルと比較した結果，帰還試料はリュウグウ表層全体を代表している事が分かった．取り出された試料の一部は既に初期分析チーム，2次キュレーションチーム，NASAへ配分され，更に国際公募研究による配布が予定されている．本稿では一連の試料取り扱いプロセス・初期記載内容について述べる．

The Committee on Space Research (COSPAR) Sample Safety Assessment Framework (SSAF) has been developed by a COSPAR appointed Working Group. The objective of the sample safety assessment would be to evaluate whether samples returned from Mars could be harmful for Earth's systems (e.g., environment, biosphere, geochemical cycles). During the Working Group's deliberations, it became clear that a comprehensive assessment to predict the effects of introducing life in new environments or ecologies is difficult and practically impossible, even for terrestrial life and certainly more so for unknown extraterrestrial life. To manage expectations, the scope of the SSAF was adjusted to evaluate only whether the presence of martian life can be excluded in samples returned from Mars. If the presence of martian life cannot be excluded, a Hold & Critical Review must be established to evaluate the risk management measures and decide on the next steps. The SSAF starts from a positive hypothesis (there is martian life in the samples), which is complementary to the null-hypothesis (there is no martian life in the samples) typically used for science. Testing the positive hypothesis includes four elements: (1) Bayesian statistics, (2) subsampling strategy, (3) test sequence, and (4) decision criteria. The test sequence capability covers self-replicating and non-self-replicating biology and biologically active molecules. Most of the investigations associated with the SSAF would need to be carried out within biological containment. The SSAF is described in sufficient detail to support planning activities for a Sample Receiving Facility (SRF) and for preparing science announcements, while at the same time acknowledging that further work is required before a detailed Sample Safety Assessment Protocol (SSAP) can be developed. The three major open issues to be addressed to optimize and implement the SSAF are (1) setting a value for the level of assurance to effectively exclude the presence of martian life in the samples, (2) carrying out an analogue test program, and (3) acquiring relevant contamination knowledge from all Mars Sample Return (MSR) flight and ground elements. Although the SSAF was developed specifically for assessing samples from Mars in the context of the currently planned NASA-ESA MSR Campaign, this framework and the basic safety approach are applicable to any other Mars sample return mission concept, with minor adjustments in the execution part related to the specific nature of the samples to be returned. The SSAF is also considered a sound basis for other COSPAR Planetary Protection Category V, restricted Earth return missions beyond Mars. It is anticipated that the SSAF will be subject to future review by the various MSR stakeholders.

火星衛星探査計画Martian Moons eXploration (MMX)は、火星衛星の一つであるフォボスからのサンプルリターンミッションである。Sample Analysis Working Team (SAWT)は、2029年に帰還するリターンサンプルの分析プロトコルの設計や、科学的要求の整理を行なっている。本発表において、MMXの科学目的である火星衛星の起源の解明等に向けて必要な分析方法と、分析チームへの分配のために必要な記載方法の検討状況を紹介する。

Japan Aerospace Exploration Agency (JAXA) will launch a spacecraft in 2024 for a sample return mission from Phobos (Martian Moons eXploration: MMX). Touchdown operations are planned to be performed twice at different landing sites on the Phobos surface to collect > 10 g of the Phobos surface materials with coring and pneumatic sampling systems on board. The Sample Analysis Working Team (SAWT) of MMX is now designing analytical protocols of the returned Phobos samples to shed light on the origin of the Martian moons as well as the evolution of the Mars-moon system. Observations of petrology and mineralogy, and measurements of bulk chemical compositions and stable isotopic ratios of, e.g., O, Cr, Ti, and Zn can provide crucial information about the origin of Phobos. If Phobos is a captured asteroid composed of primitive chondritic materials, as inferred from its reflectance spectra, geochemical data including the nature of organic matter as well as bulk H and N isotopic compositions characterize the volatile materials in the samples and constrain the type of the captured asteroid. Cosmogenic and solar wind components, most pronounced in noble gas isotopic compositions, can reveal surface processes on Phobos. Long- and short-lived radionuclide chronometry such as Mn-53-Cr-53 and Rb-87-Sr-87 systematics can date pivotal events like impacts, thermal metamorphism, and aqueous alteration on Phobos. It should be noted that the Phobos regolith is expected to contain a small amount of materials delivered from Mars, which may be physically and chemically different from any Martian meteorites in our collection and thus are particularly precious. The analysis plan will be designed to detect such Martian materials, if any, from the returned samples dominated by the endogenous Phobos materials in curation procedures at JAXA before they are processed for further analyses.

The Martian Moons Exploration (MMX) mission of the Japan Aerospace Exploration Agency (JAXA) is scheduled to launch in 2024 and aims to be the world's first mission to return a sample from Phobos. For this, JAXA is developing the MMX sampler. There is a special interest in developing the corer shooting mechanism (C-Sampler) to acquire regolith, a robotic arm to position the core sampler and transfer the acquired regolith, and a sample transfer mechanism to move the regolith to a sample return capsule. This paper reports the system design of the MMX Sampler as well as the results of the tests for the corer sampling mechanism and the regolith conditions needed for effective penetration.

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.

本発表は、2020年代に行われる火星衛星からのサンプルリターン計画(MMX: Martian Moons eXploration)によってもたらされるフォボス試料の科学意義に関する発表を行う。

火星衛星探査計画(MMX)は火星衛星フォボスからのサンプルリターン計画であり、2024年に探査機打上げを予定している。本計画では、コアリングおよび空気圧サンプリング機構により表層レゴリス試料を10 g以上回収することを目標としている。試料分析ワーキングチーム(SAWT)は現在、回収試料の分析プロトコルを作成中である。まず、試料の岩石鉱物学的観察、全岩化学組成および同位体組成から、フォボス材料物質の起源に関する情報を得る。フォボス表面で起こるプロセスは、希ガスの同位体比や試料表面の宇宙風化組織の詳細観察によって明らかになる。さらに、放射性核種による年代測定は、フォボス物質の変成作用など重要なイベントに時間的制約を与える。また、フォボスレゴリスには小天体衝突によって火星から放出された物質が少量含まれると予想されている。フォボス表面に存在するであろう火星物質は極めて貴重な試料であり、そうした物質をキュレーションの段階において発見するための手順・方法についても議論を進めている。

<jats:p>The biomolecular homochirality in living organisms has been investigated for decades, but its origin remains poorly understood. It has been shown that circular polarized light (CPL) and other energy sources are capable of inducing small enantiomeric excesses (ees) in some primary biomolecules, such as amino acids or sugars. Since the first findings of amino acids in carbonaceous meteorites, a scenario in which essential chiral biomolecules originate in space and are delivered by celestial bodies has arisen. Numerous studies have thus focused on their detection, identification, and enantiomeric excess calculations in extraterrestrial matrices. In this review we summarize the discoveries in amino acids, sugars, and organophosphorus compounds in meteorites, comets, and laboratory-simulated interstellar ices. Based on available analytical data, we also discuss their interactions with CPL in the ultraviolet (UV) and vacuum ultraviolet (VUV) regions, their abiotic chiral or achiral synthesis, and their enantiomeric distribution. Without doubt, further laboratory investigations and upcoming space missions are required to shed more light on our potential extraterrestrial molecular origins.</jats:p>

© 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.