2009 Annual Science Report
Carnegie Institution of Washington Reporting | JUL 2008 – AUG 2009
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. Finally we are studying biological contamination of meteorites once they have landed on Earth to learn how this can affect studies of the indigenous non-biological organic matter.
Task 2.1 The Outer Solar System
Co-Investigator Scott Sheppard has been observing optical colors for primitive bodies in the outer Solar System. Previous optical observations of Kuiper Belt Objects (KBOs) and Centaurs have shown some of these objects have the reddest material known in the Solar System. This ultra-red material is thought to be rich in organic matter and its color may indicate the presence of tholins produced by bombardment of simple organic ice mixtures with ionizing radiation. By observing most of the known detached disk objects, possible inner Oort cloud objects and other outer Solar System objects that exhibit extreme orbits in terms of their inclination, semi-major axis or perihelion distance, Sheppard hopes to identify color trends or correlations, in particular for the the ultra-red material, that will constrain where these extreme objects may have formed in the Solar System and thus how they may have ended up on their current orbits. This in turn will allow us to determine how the planets may have migrated and what amount of this ultra-red organic rich material may have been incorporated into the planets.
Thirty-two objects were observed to determine their optical colors in this work. All three objects that have been dynamically linked to the inner Oort cloud but have yet to pass near the Sun were found to have ultra-red surface material. Ultra-red material is generally associated with rich organics and the low inclination “cold” classical KBOs. Sheppard’s observations show very red material may be a more general feature for objects kept far from the Sun. The extended or detached disk objects, which have large perihelion distances and are thus considered to be detached from the influence of the giant planets but yet have large eccentricities, are found to have mostly moderately red colors with no ultra-red material observed.
Task 2.2 Organics in Meteorites
Co-Investigators Conel Alexander, George Cody, Larry Nittler, Andrew Steele, 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.
PI Cody performed a sophisticated multi-dimensional Solid State NMR experiment on IOM from the Murchison meteorite, revealing that up to 25 % of the carbon in IOM exists in furan moieties. Furans, e.g. furfuryl aldehyde, are readily produced through the dehydration of sugars and the most likely abiological synthesis route of sugars is through the formose condensation reaction of formaldehyde that yields a complex array of molecules and organic solids. Experiments were performed to test whether formose solids could be transformed into an organic solid similar to IOM. We find that following hydrothermal treatment, this polymer transforms into an insoluble organic solid that bears considerable chemical similarity –as determined by NMR – to IOM in primitive chondrites. Moreover, C-XANES spectra of the formose solids bear considerable, if not complete, similarity in the functional groups present in meteoritic IOM and organic matter in IDPs and some Wild-2 samples. The transformation reactions connecting formose polymer to IOM are straightforward, lending credibility to the hypothesis that chondritic IOM and cometary organic solids are ultimately derived from formose sugars. We are currently working on the kinetics of the polymerization seeking to establish under what conditions an optimum yield is obtained. We will also explore D/H exchange kinetics, nitrogen addition reactions, and thermal transformation with a view of better understanding the history of the early Solar System from the perspective of its solid phase organic constituents. A manuscript covering this research has been submitted for publication.
CoI Alexander and colleagues have continued to investigate the bulk D/H ratios of IOM from carbonaceous and ordinary chondrites In particular, the IOM of ordinary chondrites (OCs) exhibits very large D enrichments, which increase with increasing metamorphism, the most extreme dD 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. This conclusion seems to be borne out by recent analyses of clasts in the Tagish Lake (C2) meteorite that have been altered to varying degrees. We found a wide range in H/C and D enrichments (~1000‰) that apparently correlate with degree of aqueous alteration. 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.
A major recent focus of CoIs 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. The discovery that nanoglobules are abundant in IOM and, at least in the Tagish Lake and Bells meteorites, are highly enriched in D and 15N has led to intense interest in these objects, especially since their hollow spherical shapes are reminiscent of self-assembling amphiphilic molecules formed by irradiation of interstellar ice analogs. 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 seven studied meteorites, but the abundances and sizes of them vary significantly. Most 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). Some globules with highly distinctive spectra are also observed, however. For example, globule “b” in Fig. NN has a more aromatic character and a higher 15N/14N ratio than globule “a”. Globule “b” has a remarkably similar C-XANES spectrum to that of a 15N-rich nanoglobule we recently reported in a Stardust sample from comet Wild 2 as well.
CoIs Nittler, Cody and Stroud also recently published a study of a few IDPs collected during Earth’s passage through the dust stream left by earth-crossing comet Grigg-Skjellerup in 2003. These IDPs are the most primitive samples ever analyzed, in terms of their extreme abundance of presolar dust grains and highly isotopically anomalous organic matter. Raman and C-XANES analyses of the organic matter indicate that it is similar to, but even more disordered than, the most primitive IOM in meteorites. The unique properties and collection circumstances of these samples strongly suggest that they indeed formed in Grigg-Skjellerup, thus allowing for the first time the direct comparison in the laboratory of material from two known comets.
Task 2.3 Studies of Biological Contamination of Meteorites
The study of extraterrestrial organic material from Antarctic meteorites allows the direct examination of the origins and evolution of prebiotic chemistry elsewhere in the solar system. Unfortunately, the assumption that Antarctic meteorites contain minimal terrestrial organic matter has proven to be false. Antarctic meteorites are subjected to significant organic and microbial contaminants, both natural and anthropogenic, during interactions with the Antarctic ice and during recovery and curation. Without a comprehensive understanding of the baseline state of the meteorites and the sources and types of subsequent contamination, distinguishing terrestrial and extraterrestrial organic will continue to be difficult in Antarctic meteorites. CoI Steele and collaborator Marc Fries, currently at the Jet Propulsion Laboratory, continue their studies of biological contamination of primitive meteorites. The primary focus has been in-situ measurements of microbial abundance and metabolic activity, as well as quantitative laboratory analysis of anthropogenic contaminants such as petroleum products, plastics and plasticizers, and measurements of terrestrial age, terrestrial carbon fraction, and the types of microbial metabolism present as well as stable isotopic signatures of carbon, oxygen, and nitrogen. Ultra-clean samples collected in the field will be made available to other researchers for confirmatory experiments. Collaborator, Marc Fries is scheduled to participate in the next Antarctic meteorite field collection exercise, Antarctic Summer 2009-2010.
PROJECT INVESTIGATORS:George Cody
Project InvestigatorConel Alexander
Unspecified RoleAndrew Steele
Unspecified RoleRhonda Stroud
PROJECT MEMBERS:Marilyn Fogel
RELATED OBJECTIVES:Objective 2.2
Outer Solar System exploration
Sources of prebiotic materials and catalysts
Biosignatures to be sought in Solar System materials