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Project Progress

2.1. The Outer Solar System

We have continued observations, led by Co-Investigator Scott Sheppard, of bodies in the outer Solar System. We observed 51 Trans-Neptunian objects with our custom made near-infrared filters using the Gemini 8.1 meter and Magellan 6.5 meter telescopes. Our custom photometric filter system can identify surface ices with a factor of about 3 less telescope time than similar quality spectroscopic works. We can discriminate neutral bodies from water and methane ice bodies with 15 percent absorption depths, which corresponds to approximately greater than 10 percent surface fractions of ices for simple models of asteroid and Kuiper Belt object surfaces.

The Haumea family is the only known collisional family in the Kuiper Belt. The family is unique in that the objects all have very similar semi-major axes, eccentricities and inclinations and their surfaces are dominated by water ice. We found that all the small Haumea family members have deeper water ice absorption than the largest member Haumea to six sigma confidence. This observation is consistent with a collisional origin for the Haumea family. We also found a new member of the Haumea family, 2009 YE7, bringing the known family members to 11. In addition, we reject several objects with dynamics similar to Haumea because they do not show water ice on their surfaces.

We identify two non-Haumea bodies with water ice in 3:2 mean-motion resonance with Neptune (Orcus and Ixion). Combining this with previous spectroscopic studies demonstrates that moderate water ice is pervasive throughout all Kuiper Belt dynamical classes. Outside the Haumea family, we find no evidence for any correlation between body size and water ice fraction. We find that only the largest KBOs harbor methane ice, which is consistent with arguments of volatile loss timescales based on surface gravity

2.2 Organics in Meteorites

Co-Investigators 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 those at the sub-micrometer to micrometer scale.

We continued our high-profile study of organic matter in clasts from the Tagish Lake (C2) meteorite that have been altered on the parent asteroid to varying degrees, first reported last year. Both bulk (isotopic and elemental composition, NMR, XANES and FTIR spectra) and microscale (isotopic composition, TEM, XANES) properties of IOM, from the different clasts vary systematically with degree of alteration, for example indicating a loss of D-rich aliphatic material and 15N-rich nanoglobules (sub-micrometer sized hollow carbonaceous spheres present in extraterrestrial organic matter) with increasing alteration. Moreover, the abundances and nature of soluble organic molecules, including amino acids and monocarboxylic acids, also vary with parent-body alteration, demonstrating the importance of asteroidal aqueous alteration to the formation of prebiotic molecules that would have been delivered to the early Earth by carbonaceous chondrites. We have also recently begun a systematic Raman study of the IOM from the different Tagish Lake clasts to investigate how the Raman properties vary with the degree of alteration, and how this compares with our previous Raman work on IOM from various meteorite classes. The preliminary results of this cross NAI team study were published in Science. More comprehensive papers focusing on the detailed molecular spectroscopic, isotopic, and soluble molecular features of this remarkable meteorite are in preparation.

At the beginning of this funding period we also completed our work on linking IOM’s origins to formaldehyde polymerization reactions and showed that IOM in primitive chondritic meteorites is chemically related to refractory organic solids in Comet 81P/Wild 2 samples as well as both hydrous and anhydrous Interplanetary Dust Particles. We submitted a manuscript describing these studies to the Proceeding of the National Academy of Sciences and the paper was published electronically in April of 2011.

A hallmark feature of extraterrestrial organic solids is that they are characteristically enriched in deuterium relative to Solar or terrestrial values, in some cases strongly so. Our previous studies of bulk D/H on a large set of IOM isolates revealed no simple correlation between molecular structure and deuterium abundance. During the last funding period CoI’s Cody and Alexander with NAI postdoctoral fellows Kebukawa and Wang began experiments exploring the use of deuterium solid-state NMR spectroscopy to better understand deuterium enrichment in extraterrestrial solids. This is the first time that direct detection of deuterium abundance in specific functional groups has been performed on extraterrestrial organic solids. The stable hydrogen isotope system (1H and 2H) provides two NMR nuclei, thus one can measure site-specific (i.e., functional group) isotope fractionation. Such information can be used to place constraints on the origin of relatively high deuterium content in extraterrestrial organic solids relative to terrestrial water. What we have discovered is that there exists a strong fractionation of deuterium into aliphatic moieties relative to aromatic moieties; however, large shifts to total D/H are reflected in all organic functional groups. These results point to deuterium enrichment to be a relic of precursor enrichment. As formaldehyde, when observed anywhere in the galaxy, tends to be very deuterium rich; these data suggest that during the early phase of formaldehyde polymerization, hydrogen isotope exchange with deuterium depleted water lead to the formation of IOM with moderately heavy D/H. A preliminary analysis of these data was presented that the 2011 Lunar and Planetary Science Conference. A full manuscript is in preparation.

A major recent focus of Nittler, Stroud, Alexander and Cody has been on the microscale morphologies of meteoritic IOM. TEM studies of IOM from 13 meteorites reveal 3 general textures: ‘globular,’ i.e. spherical, non-porous regions approximately 50 – 1000 nm in size; ‘fluffy’, i.e. porous material with fine scale heterogeneity below 50 nm; and ‘dense-irregular’, i.e. uniformly dense, non-spherical material >50 nm. (Figure). Comparison between these morphological distinctions has shown characteristic variations in the IOM morphology, but in unexpected ways. Contrary to the results from Tagish Lake, nanoglobule abundances are fairly consistent across several different analyzed CR and CM chondrites showing a range of parent-body processing, with all of them ranging from approximately 5-7% of total IOM. Subtle variations in nanoglobule sizes have however been found with larger globules generally found in the most altered CR and CM chondrites when compared within their respective classes. When comparing the IOM morphologies as a whole, we have also been seeing a distinctive ‘coarsening’ of the IOM of the most altered chondrites (i.e. coarser IOM in CR1 GRO97755 and CM1 MET01070 compared to CR3 QUE99177 and CM2.6 QUE97990. Thus, our results show that chondrites from an assumed common parent body contain IOM with distinctive properties related to petrographic grade, affirming that parent body processing played a key role in the final state of IOM.

We have also performed systematic correlated analysis by TEM, STXM and NanoSIMS of individual nanoglobules from 9 meteorites, including the Tagish Lake clasts described above. 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.

Correlated analyses of carbonaceous material in situ in meteorite matrices are extremely valuable for better understanding the nature and origin of extraterrestrial C. Previous NanoSIMS analysis of CR3 chondrite QUE99177 identified an 8 μm long inclusion of a carbon-rich material enriched in ¹⁵N and D compared to the surrounding carbonaceous matter. We have used the FIB to lift out a cross section of this inclusion. Similarly to our coordinated approach to IOM analysis, the FIB section was analyzed with STXM, followed by TEM and NanoSIMS (Fig 2-2). The FIB- cross section of the inclusion was compared to a second FIB-extracted section of the same meteorite and previously recorded data of the IOM of the same meteorite. From the combination of the different data sets, the picture emerges that this carbon inclusion, with a size of around 8 by 6 μm, is made up almost entirely of carbon nanoglobules. The inclusion’s material appears to be more aromatic and enriched in ¹⁵N and D than the surrounding carbonaceous matter, and it is homogeneously so. There are also indications that liquid water was present at some point after the formation of the inclusion. We are currently trying to put constraints on the possible pathways that led to the formation of this inclusion and its relationship to other organic matter in the meteorite.