Interstellar Organics Research Articles

Meteorite Parent Body Aqueous Alteration Simulations of Interstellar Residue Analogs

Some families of carbonaceous chondrites are rich in prebiotic organics that may have contributed to the origin of life on Earth and elsewhere. However, the formation and chemical evolution of complex soluble organic molecules from interstellar precursors under relevant parent body conditions has not been thoroughly investigated. In this study, we approach this topic by simulating meteorite parent body aqueous alteration of interstellar residue analogs. The distributions of amines and amino acids are qualitatively and quantitatively investigated and linked to closing the gap between interstellar and meteoritic prebiotic organic abundances. We find that the abundance trend of methylamine > ethylamine> glycine > serine > alanine > \b{eta}-alanine does not change from pre- to post-aqueous alteration, suggesting that certain cloud conditions have an influential role on the distributions of interstellar-inherited meteoritic organics. However, the abundances for most of the amines and amino acids studied here varied by about 2-fold when aqueously processed for 7 days at 125 {\deg}C, and the changes in the {\alpha}- to \b{eta}-alanine ratio were consistent with those of aqueously altered carbonaceous chondrites, pointing to an influential role of meteorite parent body processing on the distributions of interstellar-inherited meteoritic organics. We detected higher abundances of {\alpha}- over \b{eta}-alanine, which is opposite to what is typically observed in aqueously altered carbonaceous chondrites; these results may be explained by at least the lack of minerals and insoluble organic matter-relevant materials in the experiments. The high abundance of volatile amines in the non-aqueously altered samples suggests that these types of interstellar volatiles can be efficiently transferred to asteroids and comets, supporting the idea of the presence of interstellar organics in solar system objects.

Alteration and Stability of Complex Macromolecular Amino Acid Precursors in Hydrothermal Environments.

The early Solar System comprised a broad area of abiotically created organic compounds, including interstellar organics which were integrated into planetesimals and parent bodies of meteorites, and eventually delivered to the early Earth. In this study, we simulated interstellar complex organic compounds synthesized by proton irradiation of a gas mixture of CO, NH3, and H2O, which are known to release amino acids after acid hydrolysis on the basis of Kobayashi et al. (1999) who reported that at the first stage of chemical evolution, the main compounds formed abiotically are complex organic compounds with high molecular weights. We examined their possible hydrothermal alteration and stabilities as amino acid precursors under high temperature and pressure conditions simulating parent bodies of meteorites by using an autoclave. We reported that all samples treated at 200-300°C predominantly released glycine and alanine, followed by α-aminobutyric acid, and serine. After heating, amino acid concentrations decreased in general; however, the recovery ratios of γ-aminobutyric acid increased with temperature. The interstellar complex organic analog could maintain as amino acid precursors after being treated at high temperature (200-300°C) and pressure (8-14MPa). However, the molecular structures were altered during heating to form organic compounds that are more stable and can survive in elevated hydrothermal conditions.

Nitrogen-included Carbonaceous Compounds (NCC): Laboratory-synthesized organics as the probable candidate for the carrier of the UIR bands observed in dusty classical novae

AbstractThe unidentified infrared (UIR) bands have been ubiquitously observed in various astrophysical environments and consist of a series of emission features arising from aromatic and/or aliphatic C-C and C-H bonds [1]. Therefore, their carriers are thought to be related to interstellar organics. However, our knowledge on the true carriers of the UIR bands is still limited. Recently [4] has proposed Mixed Aromatic Aliphatic Organic Nanoparticles, which contains hetero atoms in addition to conventional hydrocarbon models, as a more realistic interpretation of the band carriers. The challenges toward identifying the carriers of the UIR bands are still ongoing. Past studies have shown that the UIR bands observed around classical novae, which characterized by the presence of broad feature around 8μm[2], are somewhat different from those observed in other astrophysical environment. Here we report the success of experimentally synthesizing the organics called Nitrogen-included Carbonaceous Compounds (NCC; [7]) whose infrared properties can reproduce the UIR bands observed in classical novae.

Complex organics in space from Solar System to distant galaxies

Recent observational and experimental evidence for the presence of complex organics in space is reviewed. Remote astronomical observations have detected $$\sim $$ 200 gas-phased molecules through their rotational and vibrational transitions. Many classes of organic molecules are represented in this list, including some precursors to biological molecules. A number of unidentified spectral phenomena observed in the interstellar medium are likely to have originated from complex organics. The observations of these features in distant galaxies suggests that organic synthesis had already taken place during the early epochs of the Universe. In the Solar System, almost all biologically relevant molecules can be found in the soluble component of carbonaceous meteorites. Complex organics of mixed aromatic and aliphatic structures are present in the insoluble component of meteorites. Hydrocarbons cover much of the surface of the planetary satellite Titan and complex organics are found in comets and interplanetary dust particles. The possibility that the early Solar System, or even the early Earth, have been enriched by interstellar organics is discussed.

The astrobiological case for our cosmic ancestry

AbstractWith steadily mounting evidence that points to a cosmic origin of terrestrial life, a cultural barrier prevails against admitting that such a connection exists. Astronomy continues to reveal the presence of organic molecules and organic dust on a huge cosmic scale, amounting to a third of interstellar carbon tied up in this form. Just as the overwhelming bulk of organics on Earth stored over geological timescales are derived from the degradation of living cells, so it seems likely that interstellar organics in large measure also derive from biology. As we enter a new decade – the year 2010 – a clear pronouncement of our likely alien ancestry and of the existence of extraterrestrial life on a cosmic scale would seem to be overdue.

Chiral effect caused by shock waves from the supernova explosion

The chiral effect of the switch-on shock wave from the supernova (SN) on interstellar cloud organics was estimated. It was found that this effect is weak and cannot violate the chiral universality of the influence caused by left-polarized electrons and neutrino from the SN.

Presolar grains in the Solar System: Connections to stellar and interstellar organics

AbstractA small fraction of primitive meteorites and interplanetary dust particles (IDPs) consists of grains of presolar stardust. These grains have extremely unusual isotopic compositions, relative to all other planetary materials, indicating that they condensed in the outflows and explosions of prior generations of stars (Clayton & Nittler 2004). Identified presolar grain types include silicate, oxide and carbonaceous phases. The latter include graphitic carbon, diamond and SiC. Although many of these phases do not have a direct connection to organic chemistry, this is not true of the graphitic spherules. Many of these, with isotopic compositions indicating an origin in C-rich asymptotic giant branch (AGB) star outflows, have a structure consisting of naonocrystalline cores surrounded by well-graphitized C (Bernatowicz et al. 1996). The cores include isotopically anomalous polycyclic aromatic hydrocarbons (Messenger et al. 1998) and represent a link between molecular chemistry and dust condensation in stellar outflows. Meteorites and IDPs also contain abundant isotopically anomalous organic matter, including distinct organic grains, some of which probably formed in stellar outflows and/or the interstellar medium (ISM) (Busemann et al. 2006, Floss et al. 2004). In some IDPs, deuterium- and 15N-enriched organic matter is closely associated with presolar silicate grains (Messenger et al. 2005, Nguyen et al. 2007), suggesting an association in the ISM prior to Solar System formation.

Tholins and their relevance for astrophysical issues

AbstractTholins are polymeric hydrogenated carbon nitrides formed from N2:CH4 mixtures exposed to electrical discharges. They are complex disordered solids, and their structural chemistry and formation processes are not yet fully understood. Tholins have been widely adopted as useful analogs of reddish organic solids associated with planetary bodies or in interstellar space (e.g., Titan's aerosols, reddish surfaces of outer objects, interstellar organics, etc.) for fitting astronomical observations. However, there has been little evidence to date that they in fact constitute pertinent model materials, i. e. with chemical structure/composition similar to those presumed to be present in planetary or interstellar organic solids. In this contribution, we first review recent advances made regarding the determination of composition and structure of tholins produced in the laboratory. They point to a high chemical selectivity in the range of functional groups present, the control of unsaturation by nitrogen, and the highly disordered character of the structures. In a second section, we discuss the relationship between chemistry and the optical properties of tholins, and we point out the lack of a unique relationship between the shape and strength of the visible absorption bands and the chemical composition or structure of the model tholins. The tholins exhibit similarities with HCN “polymers”, that are suspected to be present in cometary refractory dust. This points to the existence of possible similar polymerisation processes, and it suggests they could also be used as analogs of N-rich cometary organics. Laboratory-based studies of cometary dust might offer new insights on the “chemical relevancy” of tholins, as combined micro-analytical techniques will allow direct comparison of chemical information between the materials produced. In a third section we present recent results pertaining to the search for such compounds in cometary grains (Stardust grains, interplanetary dust particles - IDPs). We show that some N-rich spots in stratospheric IDPs are rich in cyanide species, but no tholin-like compounds or polymeric HCN have been detected to date.

Observational constraints on the formation of interstellar methanol

AbstractThe processes by which methanol, one of the most abundant interstellar organics, is formed in the interstellar medium are not yet accurately known. Pure gas-phase chemistry models fail to reproduce observed abundances by orders of magnitude, pointing to formation on grains and subsequent desorption.Observations of methanol and its isotopologue 13CH3OH in several sources have been used to trace the origin, and thus the formation routes of methanol on interstellar grains, by means of isotope labelling a posteriori.

The origin and evolution of interstellar organics

AbstractOver the last decade, we have made great strides in better understanding dust composition and evolution in dense clouds and the diffuse interstellar medium (ISM). Thanks to improvements in IR detector sensitivity on ground-based telescopes and the Spitzer Space Telescope mission, we are no longer limited to a handful of bright background stars in order to study dust composition in quiescent dense clouds and the diffuse ISM. More thorough sampling of lines of sight in these regions has highlighted the dichotomy of the nature and composition of dust in these environments. In addition, successes in recreating interstellar processes and dust-analogs in the laboratory have helped us to understand the differences in dust absorption features we observe in the ISM. In this article, we focus on the organic components of interstellar dust, reviewing past work and highlighting the most recent observations and laboratory experiments.

Production of Complex Molecules in Astrophysical Ices

The inventory of interstellar and solar system molecules now numbers well over 100 species, including ions and molecules both charged and neutral. Gas-phase formation pathways for many of the observed organics are still uncertain, so that solid-phase syntheses are of interest. Low-temperature reactions are thought to occur within interstellar ices, on ice and grain surfaces in the interstellar medium, and on icy surfaces of solar system objects (e.g. Europa, Pluto). Ionizing radiation, such as cosmic rays, and far-UV photons are two possible initiators of such chemistry. In the Cosmic Ice Lab at NASA's Goddard Space Flight Center, we can study both the photo- and radiation chemistries of ices at 8 - 300 K. Our most-recent work has been motivated by the detections of ethylene glycol, HOCH2CH2OH, in an interstellar source (Hollis, Lovas, Jewell, et al. 2002) and in comet Hale-Bopp (Crovisier, Bockel ee-Morvan, Biver, et al. 2002). Ethylene glycol is currently the largest rmly-iden tied cometary molecule as well as one of the larger interstellar organics. This molecule's formation and accompanying chemistry provide challenges and tests for current astrochemical thought. Here we discuss laboratory experiments on ethylene glycol's solid-phase formation and de- struction. Using infrared spectroscopy, we have identied low-temperature radiation-chemical pathways that lead from known interstellar ices, such as either CH3OH or H2O and CO, to ethylene glycol. We also have identied a role for ethylene glycol in the formation of glycolalde- hyde, HOCH2C(O)H, a simple sugar (Hollis, Lovas & Jewell 2000). Related to these results are the 6- and 7-atom molecules formed by oxidation and reduction processes in irradiated H2O + C2H2 ices. Analogous experiments have been conducted on two other triply-bonded molecules in H2O-rich ice, HCN and N2. An important focus of our work is the development of reaction schemes for the formation of complex molecules within astrochemically-relevant ices, and the use of such schemes to predict new molecules awaiting detection.

Re-examining the role of chondrules in producing the elemental fractionations in chondrites

Abstract— The matrices of all primitive chondrites contain presolar materials (circumstellar grains and interstellar organics) in roughly CI abundances, suggesting that all chondrites accreted matrix that is dominated by a CI-like component. The matrix-normalized abundances of the more volatile elements (condensation temperatures <750–800 K) in carbonaceous and ordinary chondrites are also at or slightly above CI levels. The modest excesses may be due to low levels of these elements in chondrules and associated metal. Subtraction of a CI-like matrix component from a bulk ordinary chondrite composition closely matches the average composition of chondrules determined by instrumental neutron activation analysis (INAA) if some Fe-metal is added to the chondrule composition. Measured matrix compositions are not CI-like. Sampling bias and secondary redistribution of elements may have played a role, but the best explanation is that ˜10–30% of refractory-rich, volatile depleted material was added to matrix. If most of the more volatile elements are in a CI-dominated matrix, the major and volatile element fractionations must be largely carried by chondrules. There is both direct and indirect evidence for evaporation during chondrule formation. Type IIA and type B chondrules could have formed from a mixture of CI material and material evaporated from type IA chondrules. The Mg-Si-Fe fractionations in the ordinary chondrites can be reproduced with the loss of type IA chondrule material and associated metal. The loss of evaporated material from the chondrules could explain the volatile element fractionations. Mechanisms for how these fractionations occurred are necessarily speculative, but two possibilities are briefly explored.

Biomolecules in the interstellar medium and in comets

We review recent studies of organic molecule formation in dense molecular clouds and in comets. We summarise the known organic inventories of molecular clouds and recent comets, particularly Hale-Bopp. The principal chemical formation pathways involving gas phase reactions, as well as formation by catalytic reactions on grain surfaces or through dust fragmentation, are identified for both dense clouds and cometary comae. The processes leading to organic molecules with known biological function, carbon chains, deuterium fractionation, HNC and S-bearing compounds are described. Observational searches for new interstellar organics are outlined and the connection between observed interstellar organics and those detected in comets Hale-Bopp and Hyakutake are discussed.

The role of Fischer‐Tropsch catalysis in solar nebula chemistry

Abstract— Fischer‐Tropsch catalysis, the iron/nickel catalyzed conversion of CO and H2 to hydrocarbons, would have been the only thermally‐driven pathway available in the solar nebula to convert CO into other forms of carbon. A major issue in meteoritics is to determine the origin of meteoritic organics: are they mainly formed from CO in the solar nebula via a process such as Fischer‐Tropsch, or are they derived from interstellar organics? In order to determine the role that Fischer‐Tropsch catalysis may have played in the organic chemical evolution of the solar nebula, we have developed a kinetic model for this process. Our model results agree well with experimental data from several existing laboratory studies. In contrast, empirical rate equations, which have been derived from experimental rate data for a limited temperature (T) and pressure (P) range, are inconsistent with experimental rate data for higher T and lower P.We have applied our model to pressure and temperature profiles for the solar nebula, during the epoch in which meteorite parent bodies condensed and agglomerated. We find that, under nebular conditions, the conversion rate of CO to CH4 does not simply increase with temperature as the empirically‐derived equations suggest. Instead, our model results show that this process would have been most efficient in a fairly narrow region that coincides with the present position of the asteroid belt. Our results support the hypothesis that Fischer‐Tropsch catalysis may have played a role in solar nebula chemistry by converting CO into less volatile materials that can be much more readily processed in the nebula and in parent bodies.

On The Nature of Interstellar Organic Chemistry

AbstractA theory for the origin of all organic molecules observed in regions of massive and low-mass star formation, as well as in dark molecular clouds is described. On dust grains, single atom addition reactions and stability of the intermediate radicals, mechanisms similar to those believed to form the organic component of the Murchison meteorite, lead to a very limited number of mantle compositions depending upon the degree of hydrogenation. The key step in the theory is the formation of the formyl radical by H atom addition (by quantum tunnelling) to CO. Subsequent H atom additions lead to formaldehyde and methanol, as previously suggested; C, N, and O atoms can also undergo additions to HCO. For increasing hydrogenation, the mantle types include one in which there is little contribution from formyl-initiated chemistry; one in which an acetylenic chain develops through C atom additions; and others where the acetylenic chain is increasingly hydrogenated to form aldehydes and alcohols. Following evaporation of grain mantles, such as occurs in protostellar «hot cores», these molecules can form new organics, for example, by alkyl cation transfer from alcohols. In dark clouds, different mantles lead to different gas phase organics. This scenario accounts naturally for the formation of many interstellar organics for which none presently exists, predicts observable correlations between specific interstellar molecules, indicates the presence of many new organic molecules and why several others are not observed.

Interstellar organics found in meteorites

Interstellar organics found in meteorites

Approaching the Interstellar Grain Organic Refractory Component

Infrared spectra have been obtained for laboratory residues of photoprocessed low-temperature ices which have been exposed to long-term solar ultraviolet radiation on the EURECA satellite. This is an analog to the ultraviolet processing of interstellar dust mantles in diffuse clouds after leaving molecular clouds. The 3.4 μm absorption features of these organic materials match those of the diffuse cloud interstellar dust better than any other previously suggested analog to the interstellar organics.

The formation of organic molecules in astronomical ices

An absorption feature at 3.4 μm has been observed in various lines-of-sight through the diffuse interstellar medium. Its position and width lead to an identification with the CH stretching mode of solid organic material. A possible mechanism for the production of organic solids in the interstellar medium is UV photoprocessing of icy mantles which accrete on dust grains in dense clouds. Furthermore, thermally induced reactions involving formaldehyde molecules in the mantles could be an important source of organics. Laboratory simulation of these processes shows that a large variety of oxygen- and nitrogen-rich species may be produced. It is shown that the occurrence of periodic transient heating events plays an important role in the production of organic material in the ice mantles. Finally, it is pointed out how future missions like the Infrared Space Observatory (ISO) as well as analysis of comet material by Rosetta may be able to clarify the nature and evolution of interstellar organics.