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Home , Interstellar medium, THEO, Volatiles

Geochemical Journal, Vol. 48, pp. 509 to 510, 2014 doi:10.2343/geochemj.2.0349

Preface: Evolution of refractory grains, volatiles, and organic from the interstellar medium to the early

SHOGO TACHIBANA,1* HENNER BUSEMANN2 and LYDIE BONAL3

1Department of Natural History Sciences, Hokkaido University, N10W8, Kita-ku, Sapporo, Hokkaido 060-0810, Japan 2Inst. für Geochemie und Petrologie, ETH Zürich, NW C 84, Clausiusstrasse 25, CH-8092 Zürich, Switzerland 3Institut de Planétologie et d’Astrophysique de Grenoble, IPAG/PLANETO, Bâtiment D de Physique - BP 53, 38041 Grenoble Cedex 9, France

Primitive extraterrestrial materials record the early evo- by photolysis and/or radiolysis of in laboratories do lution of the solar system that predated formation. not match the entire spectral features of IOMs They also preserve the interstellar heritage from prior to either. These lines of evidences indicate that further evo- the ’s birth in the form of and poten- lution of organic materials may have occurred in the early tially as isotopic signatures of light elements in organic stage of solar-system formation from ISM carbonaceous and specific molecules. It is one of the key issues dust as a precursor. in to link the birth and evolution of the The evolution of organic matter in the early solar sys- solar system to the evolution of the interstellar medium tem may also be recorded in soluble organic components (ISM) and the . To address this issue, an interdis- extracted from primitive . Yamashita and ciplinary approach linking analysis of extraterrestrial Naraoka (2014) report two homologous series of materials including samples returned by spacecraft, labo- alkylpyridines (CnH2n–5N and CnH2n–7N) identified in the ratory experiments, astronomical observations, and theo- extract of the Murchison by retical studies is crucial. chromatography/high-resolution spectrometry. The This special issue arose from a session “Refractory organic components consisting of C, H, and N are likely Grains, Volatiles, and Organic Molecules Inherited from to have escaped chemical oxidation during the Interstellar Medium” at the Goldschmidt Conference alteration and may thus record the early stage of forma- (Aug. 25–30, 2013, Florence Italy) and consists of six tion of meteoritic organic components. Laboratory simu- articles covering a wide array of topics and disciplines to lation experiments involving HCHO, CH3CHO, and NH3 explore various perspectives of cosmochemistry; astro- produced alkylpyridines, which provided a plausible syn- nomical observation, laboratory experiments, extraterres- thetic pathway for meteoritic alkylpyridines via aldol trial organic chemistry, astrophysical modeling, in-situ condensation and Chichibabin-type reactions isotopic analyses, chronology, and sample-return mission. (alkylpyridine formation from aldehydes and NH3). Their Dartois et al. (2014) summarize observational and findings indicate the possible importance of aldehyde laboratory studies on interstellar carbonaceous dust to activity under alkaline conditions in the presence of am- explore the link between ISM carbonaceous dust and in- monia for the chemical evolution of soluble organic mat- soluble organic matter (IOM) found in and ter in carbonaceous chondrites. interplanetary dust particles (IDPs). Several forms of is one of the dominant volatile components in carbonaceous solids are observed in the ISM the solar system, and played many essential roles in solar (polyaromatic hydrocarbons (PAHs), amorphous , system chemistry through interactions with minerals and hydrogenated amorphous carbons (a-C:H), fullerenes, and organic matter. Tornow et al. (2014) model the forma- that further turn into macromolecular organic residues tion, destruction and re-formation of water molecules after ice-sublimation), among which PAHs, a-C:H and/or during the earliest stage of formation (a quasi- macromolecular organic residues would be the main pre- stationary core and its collapse to form cursor of solar system carbonaceous materials. PAHs and a ) focusing on the evolution of the D/H ratio. a-C:H are more aromatic and contain less and Their model show that the D/H ratios of water in the than solar-system IOM. Organic matter formed and dust phases change spatially and temporally and that their D/H ratios are higher than the solar-system meteoritic water. The model thus infers that the relatively low D/H *Corresponding author (e-mail: [email protected]) ratio of solar-system meteoritic water may be related to Copyright © 2014 by The Geochemical Society of Japan. the later evolutional stage of the protosolar disk.

509 The inner solar system water might have had low D/H sions are the only way to obtain such pristine materials ratios, but it has not yet been clear how many water with geologic context and without terrestrial contamina- sources were present in the early solar system and how tion. The samples from the surface of this will such water inventories interacted with each other. also provide a precious opportunity to study current sur- Yurimoto et al. (2014) report the first H and O isotope face geological activities and the orbital evolution of the measurements of asteroidal liquid water, found as fluid asteroid. The and NASA’s OSIRIS-REx inclusions in halite from two H chondrites sample-return mission to the B-type asteroid Bennu (Monahans and Zag), with a secondary mass (2016–2023) (Lauretta et al., 2014) will open a new era spectrometer equipped with a cryo-sample stage (Cryo- in cosmochemistry in the early 2020’s. SIMS). Highly variable H and O isotopic compositions Finally we are grateful to all the authors for their con- were found in the fluids inclusions; –400 < δD < +1300‰ tributions and all the reviewers for their constructive and and –20 < ∆17O < +30‰. This indicates that asteroidal meaningful reviews. We also thank Prof. Hisayoshi aqueous fluids had at least two sources (inner solar- Yurimoto, the chef editor of Geochemical Journal, and system chondritic water and outer solar-system cometary the journal editorial office for this precious opportunity water) and that the fluids with various mixing degrees of the special issue on cosmochemistry and their kind were in isotopic disequilibrium before trapped into halite assistance and patience throughout the editorial process. on the parent body (bodies) of H chondrites. Yurimoto et al. (2014) concluded that such various degrees of water- REFERENCES rock interaction on may be the fundamen- tal evolution pathway of planetary water. 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