Non-protein amino acids identified in carbon-rich Hayabusa particles

Amino acid abundances in acid-hydrolyzed hot water extracts of gold foils containing five Category 3 (carbon-rich) Hayabusa particles were studied using liquid chromatography with tandem fluorescence and accurate mass detection. Initial particle analyses using field emission scanning electron microscopy with energy-dispersive X-ray spectrometry indicated that the particles were composed mainly of carbon. Prior to amino acid analysis, infrared and Raman microspectroscopy showed some grains possessed primitive organic carbon. Although trace terrestrial contamination, namely l-protein amino acids, was observed in all Hayabusa extracts, several terrestrially uncommon non-protein amino acids were also identified. Some Hayabusa particles contained racemic (d approximate to l) mixtures of the non-protein amino acids beta-aminoisobutyric acid (beta-AIB) and beta-amino-n-butyric acid (beta-ABA) at low abundances ranging from 0.09 to 0.31 nmol g(-1). Larger abundances of the non-protein amino acid beta-alanine (9.2 nmol g(-1), approximate to 4.5 times greater than background levels) were measured in an extract of three Hayabusa particles. This beta-alanine abundance was approximate to 6 times higher than that measured in an extract of a CM2 Murchison grain processed in parallel. The comparatively high beta-alanine abundance is surprising as asteroid Itokawa is similar to amino acid-poor LL ordinary chondrites. Elevated beta-alanine abundances and racemic beta-AIB and beta-ABA in Hayabusa grains suggested these compounds have non-biological and plausibly non-terrestrial origins. These results are the first evidence of plausibly extraterrestrial amino acids in asteroid material from a sample-return mission and demonstrate the capabilities of the analytical protocols used to study asteroid Ryugu and Bennu samples returned by the JAXA Hayabusa2 and NASA OSIRIS-REx missions, respectively.

Automated summary

This study investigated the amino acid abundances in acid-hydrolyzed hot water extracts of gold foils containing five Category 3 Hayabusa particles. The results revealed the presence of uncommon non-protein amino acids, suggesting a non-biological and likely non-terrestrial origin for these compounds.