Isotopic compositions and functional chemistry of meteoritic organic matter revealed by high spatial resolution mass spectrometry – synchrotron spectroscopy – electron microscopy techniques

The isotopic and chemical properties of organic matter (OM) in extraterrestrial samples record a combination of presolar, nebular, parent-body, and terrestrial processes, which can be disentangled by high-spatial resolution studies [e.g., 1]. These studies have the advantage that they also allow for analysis of the petrographic relationship to the matrix and require only minimal chemical treatment. Here we have investigated OM properties within two recent observed falls, Tarda and Winchcombe, by combined “in-situ” techniques. Carbon and nitrogen isotopic compositions were studied by NanoSIMS. OM was sectioned by the focused ion beam (FIB) technique (Hitachi Ethos NX5000). Scanning Transmission X-Ray Microscopy (STXM) was performed at the I08 beamline of Diamond Light Source. Low-kV electron energy loss spectroscopy (EELS) in the vibrational and core loss regimes was performed with a monochromated, aberration-corrected Nion UltraSTEM 100MC. Nitrogen and carbon isotopic compositions of OM aggregates and nanoglobules in Tarda show a range of δ15N values from close-to-terrestrial to ~600‰ with close-to-terrestrial or slightly heavy δ13C values. Single hotspots reach >1000‰ in δ15N and ~80‰ in δ13C, but no negative δ15N values similar to Maribo OM have been detected [2]. STXM analyses at the C K-edge show that OM in Winchcombe is typical for OM in primitive meteorites, with strong absorption at the aromatic C=C (~285 eV) and the ketone/aldehyde (~286.6 eV) bands. The presence of reactive double and triple C-N bonding is a strong indicator that some OM is still pristine.

[1] Van Kooten et al. GCA 2018, [2] Vollmer et al. SciRep 2020.