¹Surjyendu Bhattacharjee,¹John M. Eiler
Geochimica et Cosmochimica Acta (in Press) Link to Article [https://doi.org/10.1016/j.gca.2024.07.013]
¹California Institute of Technology, 1200 E. California Blvd., Pasadena, CA 91125, USA
Copyright Elsevier

We report theoretically calculated equilibrium oxygen isotopic fractionation factors (17O/16O, 18O/16O) between a set of representative O-bearing organic molecules and water, as well as site specific 13C, 15N and 13C-18O equilibrium clumped isotopic anomalies in these compounds, all computed using density functional theory (DFT) methods combined with Urey-Bigeleisen-Mayer (UBM) calculations of reduced partition function ratios. We performed density functional theory (DFT) calculations with the B3LYP exchange correlation functional, and explored different basis sets, and treatments of solvation. After benchmarking results against prior theoretical and empirical studies, we conclude that B3LYP level of theory and aug-cc-pVTZ basis set with cluster solvation provides the most accurate treatment of this problem within the constraints of our approach. A representative set of O bearing organic compounds including aldehyde, ketones, amino acid and aromatic alcohol are predicted to be ∼24–41 ‰ higher in 18O/16O relative to water with θcompound – water varying in the range 0.522 – 0.526; and ∼ 23–41 ‰ lower in 13C/12C and ∼ 11 ‰ higher in 15N/14N relative to CO2 and N2, respectively (all presuming equilibrium partitioning) at 273 K.

This study is motivated by the study of soluble organic molecules found in carbonaceous chondrite meteorites, a significant fraction of which contain oxygen in their structure in the form of functional groups such as carbonyl, carboxylic acid, ester, ethers, and alcohol. These samples also contain oxygen-bearing macromolecular organic matter. We use the fractionation factors presented here to predict the triple oxygen isotope compositions of these organics, assuming equilibration with previously proposed early-solar-system volatile reservoirs and environments of organic synthesis.

¹Devin L. Schrader et al. (>10)
Geochimica et Cosmochimica Acta (in Press) Link to Article [https://doi.org/10.1016/j.gca.2024.07.007]
¹Buseck Center for Meteorite Studies, School of Earth and Space Exploration, Arizona State University, Tempe, AZ 85287, USA
Copyright Elsevier

We report a comprehensive study of the ungrouped type 2 carbonaceous chondrite, Tarda, which fell in Morocco in 2020. This meteorite exhibits substantial similarities to Tagish Lake, Wisconsin Range 91600, and Meteorite Hills 00432, which are generally considered to have originated from a D-type asteroid(s). We constrain the compositions and petrologies of the materials present in a potential sample of a D-type asteroid by reporting the petrography, bulk chemical compositions, bulk H, C, N, Cr, and Ti isotopic compositions, reflectance spectra, and in situ chemical compositions of metals, sulfides, carbonates, and FeO-poor and FeO-rich chondrule silicates of Tarda. We also present new data for Tagish Lake. We then compare Tarda with the other Tagish Lake-like meteorites.
Tarda and Tagish Lake appear to be from the same parent body, as demonstrated by their similar petrologies (modal abundances, chondrule sizes), mineral compositions, bulk chemical and isotopic compositions, and reflectance spectra. While the two other Tagish Lake-like meteorites, Wisconsin Range 91600 and Meteorite Hills 00432, show some affinities to Tagish Lake and Tarda, they also share similar characteristics to the Mighei-like carbonaceous (CM) chondrites, warranting further study. Similarities in reflectance spectra suggest that P-type asteroids 65 Cybele and 76 Freia are potential parent bodies of Tarda and the Tagish Lake-like meteorites, or at least have similar surface materials. Since upcoming spacecraft missions will spectrally survey D-type, P-type, and C-type Trojan asteroids (NASA’s Lucy) and spectrally study and return samples from Mars’ moon Phobos (JAXA’s Martian Moons eXploration mission), which is spectrally similar to D-type asteroids, these meteorites are of substantial scientific interest. Furthermore, since Tarda closely spectrally matches P-type asteroids (but compositionally matches the D-type asteroid like Tagish Lake meteorite), P-type and D-type asteroids may represent fragments of the same or similar parent bodies.