2010 Annual Science Report
Carnegie Institution of Washington Reporting | SEP 2009 – AUG 2010
Project 2: Origin and Evolution of Organic Matter in the Solar System
Through telescopic observations of remote objects, we are learning about the distribution of organic matter in the outer Solar System and how it is thermally processed, as well as about dynamic processes that .could have delivered such organic-rich material to be incorporated into terrestrial planets. Extraterrestrial samples like primitive meteorites and interplanetary dust particles contain significant amounts of carbonaceous material and were likely a source of organic matter to the early Earth. By using a wide variety of advanced techniques to study organic matter in meteorites and other extraterrestrial samples, we are trying to learn how and where it formed, and how it has been modified during 4.5 billion years of solar system evolution. We also perform laboratory experiments to simulate formation of complex organic matter and how it is modified on planetary surfaces.
Task 2.1 The Outer Solar System
CoI Scott Sheppard has continued observing optical colors for extreme bodies in the outer Solar System. Extreme objects have possible origins beyond the Kuiper belt edge, high inclinations, very large semi-major axes or large perihelion distances. All objects linked to the Oort cloud show ultra-red colors. Ultra-red material is generally associated with rich organics and the low inclination “cold” classical Kuiper Belt objects. Sheppard’s observations show very red material may be a more general feature for objects kept far from the Sun. All the objects in Halley comet like periods and inclinations but with perihelia in the outer solar system show more neutral surfaces indicating they have either come from a different source region than the Oort Cloud or that their surfaces have been recently thermally modified. Sheppard has also shown that the colors of the detached disk objects are similar to the scattered disk and Halley like objects indicating common surface properties. There is also a clear trend that objects more distant and kept far from the Sun appear redder.
Task 2.2 Organics in Meteorites and Comets
CoIs Conel Alexander, George Cody, Larry Nittler, and Rhonda Stroud have continued an active research program on extraterrestrial organic carbon, performing structural, molecular and isotopic analyses on insoluble organic matter (IOM) isolated from a broad range of meteorites (spanning multiple classes, groups, and petrologic types) as well as on organic matter in situ in meteorites, interplanetary dust particles (IDPs) and comet Wild-2 samples. The studies focus on both the macroscopic “bulk” properties and the sub-micrometer to micrometer scale ones.
Co-Is Alexander, Cody, Nittler and colleagues have continued to investigate the bulk D/H ratios of IOM from carbonaceous and ordinary chondrites (recently published in Geochimica Cosmochimica Acta). In particular, the IOM of ordinary chondrites (OCs) exhibits very large D enrichments, which increase with increasing metamorphism, the most extreme δD value measured being almost 12,000‰. Such large isotopic fractionations could be produced in the OC parent bodies through the loss of isotopically very light H2 generated when metal was oxidized by water at low temperatures (<200°C). Similar isotopic fractionations were not generated in the IOM of metamorphosed CV and CO chondrites, possibly because proportionately much less H2 was generated in them during parent body processing. Although hydrogen would also have been generated during the alteration of CI, CM and CR carbonaceous chondrites, we have concluded that the most isotopically anomalous IOM compositions in these meteorites are probably closest to their primordial values. The less isotopically anomalous IOM compositions have probably been modified by parent body processes.
Recent analyses of clasts in the Tagish Lake (C2) meteorite that have been altered to varying degrees are providing new insights into the role of parent-body processing on IOM. We found a wide range in H/C and D enrichments (~1000‰) that apparently correlate with degree of aqueous alteration. At the microscale, less-altered clasts exhibit a greater degree of isotopic heterogeneity (e.g., D and 15N hotspots) and abundance of so-called nanoglobules (Figure). We are currently preparing larger samples for analysis by NMR and other techniques to try to understand how the structure and functional group chemistry of the IOM has been modified. This should provide important clues about the mechanism(s) of the modification experienced by the IOM, and which functional groups are the main D carriers.
CoIs Cody and Alexander worked with Post Doctoral fellow Yoko Kebukawa completed a systematic FTIR study of insoluble organic matter (IOM) isolated from multiple chondrite classes, groups, and petrological type. This program, led by Kebukawa, provides a unique perspective into the molecular structure of IOM. We find that based on the vibrational spectra fine structure that we can separate IOM into four distinct groups. Group A includes all primitive petrologic type 1 & 2 chondrites. Group B is found to correspond to unambiguously to type 3.0 chondrites. The interesting aspect arises when one looks at the metamorphosed type 3 chondrites. Here we find a remarkable bifurcation in molecular structure. Amongst the type 3+ chondrites we have discovered two discrete groups as defined by their distinctly different vibrational spectra. This was not expected. The difference we observe between these two groups may be interpreted as resulting from differences in the activity of oxygen during metamorphism. It appears that the molecular structure of organic solids provides information that is not available or obvious in the inorganic constituents. A manuscript describing this research has been submitted to Geochimical Cosmochimica Acta.
Over the past year we have been developing and optimizing a strategy to obtain solid-state deuterium NMR of extraterrestrial organic solids. As a result of previously funded research we have discovered that there exists a very complex relationship between deuterium enrichment and the metamorphic state of chondritic organic matter. It has taken considerable time to optimize the experimental parameters of this experiment, but are now successfully observing D in chondritic IOM at natural abundance. That we observe any signal at all is remarkable as recent work by others concluded that deuterium lies within ~ 0.1 nm of an unpaired electron. Were this to be correct then D would be undetectable via NMR. We are currently comparing how the distribution of D and H vary organic functional groups. We expect that the results of this study will have profound implications on our understanding of isotropic enrichment in extraterrestrial materials.
For the past year we have been focusing the potential role of formaldehyde polymerization on the synthesis of primitive organic solids. This research program has several components. First CoI Cody working with PD Kebukawa have been studying the thermokinetics of formaldehyde polymerization in order to determine how much time is required for high levels of polymerization. We have discovered that the polymerization is strongly controlled by monomer diffusion and have developed an adequate mathematical description of the reaction. Interestingly, we find that the correct polymerization regime requires lower temperatures. At high temperatures the polymerization is hindered and the ultimate yields are low. This research was presented at the Meteoritical Society meeting in New York. In parallel, CoIs Cody and Stroud, working in collaboration with Scott Sandford (NASA Ames-NAI team), Michel Nuevo (NASA Ames), and Stephanie Milam (NASA GSFC), studied the polymeric films that form after low temperature UV-irradiated formaldehyde containing ices. These analyses were performed at the Advanced Light Source. A publication outlining these studies has been submitted to Advances in Space Research.
A major recent focus of Nittler, Stroud, Alexander and Cody has been on so-called “nanoglobules,” tiny hollow organic spheres now known to be represent a portion of the IOM in primitive meteorites, IDPs and even Wild-2 samples (as we reported in a recent paper in Geoochimica Cosmichimica Acta). A correlated approach of systematically analyzing the same nanoglobules by TEM, STXM and SIMS is providing new insights into the distribution, origin and processing history of these enigmatic objects. We have found nanoglobules to be present in nine studied meteorites, including the new Tagish Lake clasts described above, but the abundances and sizes of them vary significantly. Interestingly, we find that within a single meteorite, many globules show similar C-XANES spectra to the bulk IOM, but with slightly enhanced C-O bonding (e.g. carboxyl and vinyl-keto groups). However, a fraction of globules in all studied meteorites show distinct C-XANES spectra, with a primarily aromatic character and little C-O bonding. The data point to multiple origins and responses to parent-body processing of nanoglobules.
PROJECT INVESTIGATORS:George Cody
Project InvestigatorConel Alexander
Unspecified RoleAndrew Steele
Unspecified RoleRhonda Stroud
PROJECT MEMBERS:Marilyn Fogel
Bradley De Gregorio
RELATED OBJECTIVES:Objective 2.2
Outer Solar System exploration
Sources of prebiotic materials and catalysts
Biosignatures to be sought in Solar System materials