High resolution electron microscopy (UltraSTEM) of the most primitive organic materials in chondrite parent bodies and comets - Formation and evolution of the organic inventory of early Earth.

• Applicant: Dr. Christian Vollmer
• Subject Area: Palaeontology
• Term: from 2015 to 2021
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 276966992

Carbonaceous materials were a widespread constituent of the early solar system and hence part of the initial organic inventory of the terrestrial planets. These materials are today preserved in the most primitive carbonaceous chondrites or interplanetary dust particles (IDPs) originating from comets and have not been overprinted by prolonged thermal metamorphism. A tiny fraction of this carbonaceous matter carries fingerprints of low temperature fractionation reactions as isotope enrichments in, e.g., 15N or D. These isotopically anomalous carbonaceous grains have therefore recorded processes in the cold parent molecular cloud of our solar system or the outer reaches of the young solar nebula. Investigations on these grains are therefore key to unravel the evolution of the most primitive organic compounds that were incorporated into the solar system and therefore finally also into the terrestrial planets and the Earth. As Earth has probably lost most volatiles during differentiation or the moon-forming impact, a late addition of organic matter by asteroids or comets is of crucial interest here. In this project, we will investigate these primitive organic materials by an aberration-corrected scanning transmission electron microscope (UltraSTEM) that is exceptionally suited to study these beam-sensitive grains owing to its low acceleration voltage below the knock-on damage threshold of carbon (~ 80 keV). The unique instrumental setup of this microscope also allows to analyse the electronic bonding configuration of organic matter (e.g., aromatic or aliphatic) with high spatial resolution (~ 0.1 nm) that is not achievable by other methods (e.g., synchrotron spectroscopy). First published results (Vollmer et al. 2014) obtained recently by UltraSTEM analyses on isotopically anomalous organic grains from meteorites and IDPs have shown that fluid-induced parent body reactions can transform fragile pristine organic grains by subtle synthesis processes on a very fine scale. We want to expand on these promising results by analyzing a larger set of isotopically anomalous organic grains from diverse primitive meteorites and cometary samples to search for further evidence of these fluid reactions and to build up a catalogue of the most primitive organic compounds in different parent bodies. These investigations will help to understand the evolution of organic matter in the early solar nebula to more complex molecules important for the origin of life on early Earth.

• DFG Programme: Priority Programmes
• Subproject of: SPP 1833: Building a Habitable Earth
• International Connection: Netherlands, United Kingdom
• Cooperation Partners: Professor Dr. Henner Busemann; Dr. Arne Janssen; Dr. Demie Kepaptsoglou; Dr. Jan Leitner; Professor Dr. Quentin Ramasse