Proto-Planetary Disk Chemistry Recorded by D-Rich Organic Radicals in Carbonaceous Chondrites

Abstract

Insoluble organic matter (IOM) in primitive carbonaceous meteorites has preserved its chemical composition and isotopic heterogeneity since the solar system formed ∼4.567 billion years ago. We have identified the carrier moieties of isotopically anomalous hydrogen in IOM isolated from the Orgueil carbonaceous chondrite. Data from high spatial resolution, quantitative isotopic NanoSIMS mapping of Orgueil IOM combined with data from electron paramagnetic resonance spectroscopy reveals that organic radicals hold all the deuterium excess (relative to the bulk IOM) in distinct, micrometer-sized, D-rich hotspots. Taken together with previous work, the results indicate that an isotopic exchange reaction took place between pre-existing organic compounds characterized by low D/H ratios and D-rich gaseous molecules, such as H 2 D + or HD 2 +. This exchange reaction most likely took place in the diffuse outer regions of the proto-planetary disk around the young Sun, offering a model that reconciles meteoritic and cometary isotopic compositions of organic molecules.

Organic material in meteorites and the link to the origin of life

“…No D-rich hot spots are observed in IOM of heated chondrites, i.e. CO, CV [60] pointing out to their thermal sensitivity. The distribution of the deuterium has also been studied at the molecular scale [61,62].…”

“…It must be EPOV 2012 03001-p. 5 noted that the lowest isotopic enrichment was measured in Abee enstatite chondrite (δD = -480 ‰; D/H = 80×10 -6 ) [56,57]. Isotopic imaging has revealed that H isotopes can exhibit large variations in the IOM of CI, CM and CR chondrites with the occurrence of D-rich " hot spots": micron sized areas with large positive D anomalies (figure 3), which could go up to δD = 8000 ‰ (D/H=1402×10 -6 ; [58][59][60]). No D-rich hot spots are observed in IOM of heated chondrites, i.e.…”

Organic material and gases in the early Solar System : the meteorite record

“…No D-rich hot spots are observed in IOM of heated chondrites, i.e. CO, CV (Remusat et al 2009) pointing out to their thermal sensitivity.…”

“…Busemann et al 2006;Nakamura-Messenger et al 2006;Remusat et al 2009). No D-rich hot spots are observed in IOM of heated chondrites, i.e.…”

“…In such a scenario, D-rich hot spots would represent remnant grains of interstellar D-rich organic material that would not be affected by parent body processes Nakamura-Messenger et al 2006). However, another hypothesis (Gourier et al 2008;Remusat et al 2009) suggests that the D-rich hot spots correspond to radical rich regions as organic radicals are D-rich and are heterogeneously distributed. As the radicals may have formed in the protosolar nebula, it would imply a local origin (i.e.…”