Toward an experimental synthesis of the chondritic insoluble organic matter

Abstract

International audienceBased on the statistical model proposed for the molecular structure of the insoluble organic matter (IOM) isolated from the Murchison meteorite, it was recently proposed that, in the solar T-Tauri disk regions where (photo)dissociation of gaseous molecules takes place, aromatics result from the cyclization/aromatization of short aliphatics. This hypothesis is tested in this study, with n-alkanes being submitted to high-frequency discharge at low pressure. The contamination issue was eliminated using deuterated precursor. IOM was formed and studied using solid-state nuclear magnetic resonance, pyrolysis coupled to gas chromatography and mass spectrometry, RuO4 oxidation, and high-resolution transmission electron microscopy. It exhibits numerous similarities at the molecular level with the hydrocarbon backbone of the natural IOM, reinforcing the idea that the initial precursors of the IOM were originally chains in the gas. Moreover, a fine comparison between the chemical structure of several meteorite IOM suggests either that (i) the meteorite IOMs share a common precursor standing for the synthetic IOM or that (ii) the slight differences between the meteorite IOMs reflect differences in their environment at the time of their formation i.e., related to plasma temperature that, in turn, dictates the dissociation–recombination rates of organic fragments

Hydrogen isotopic exchange kinetics between organic matter and water: Implications for chemical evolution during meteorite parent body processing

“…Whether macromolecular organic matter in chondrites was synthesized via the formaldehyde scenario (Cody et al 2011) or in other environments via different processes, e.g., UV irradiation of icy particles (e.g., Muñoz Caro and Dartois 2013), plasma discharge (e.g., Biron et al 2015;Kuga et al 2015), or Fischer-Tropsch type reactions (e.g., Anders et al 1973;Nuth et al 2008), stable macromolecular organic matter however formed was then subjected to hydrogen isotopic exchange during planetesimal alteration processes. One can use the COA as an analog of chondritic macromolecules due to its very close similarities to chondritic IOM at the molecular functional group level (Cody et al 2011;Kebukawa et al 2013).…”

“…There are many possible IOM formation scenarios-UV irradiation to icy particles (e.g., Muñoz Caro and Dartois 2013), plasma discharge (e.g., Biron et al 2015;Kuga et al 2015), and Fischer-Tropsch type reactions (e.g., Nuth et al 2008). Among these, a possible scenario of IOM formation has been proposed starting with interstellar formaldehyde (Cody et al 2011).…”

Hydrogen isotope fractionation in methane plasma

“…In addition, organic radicals account Another similarity lies on the molecular structure of both chondritic and synthetic IOM. In a side experiment, the IOM synthesized from octane plasma was investigated through various spectroscopic and degradative techniques and was shown to reproduce most of the hydrocarbon skeleton features of the chondritic IOM (20). The synthetic IOM from the CH 4 plasma is also similar to that synthesized from octane plasma (17).…”

Definition and use of functional analogues in planetary exploration

“…Since, by definition, a molecule has a given formula (negating purity considerations), most can be purchased from specialised companies. Nevertheless, certain molecules or mixtures, such as insoluble organic matter similar to that detected in meteorites, or tholins observed on Titan, cannot be purchased, but are instead synthesised under analogue conditions using simulation chambers, albeit generally in limited quantities (Brass e et al, 2017;Alcouffe et al, 2010;Biron et al, 2015).…”