The Origin of Amino Acids in Lunar Regolith Samples

We analyzed the amino acid content of seven lunar regolith samples returned by the Apollo 16 and Apollo 17 missions and stored under NASA curation since collection using ultrahigh-performance liquid chromatography with fluorescence detection and time-of-flight mass spectrometry. Consistent with results from initial analyses shortly after collection in the 1970s, we observed amino acids at low concentrations in all of the curated samples, ranging from 0.2 parts-per-billion (ppb) to 42.7ppb in hot-water extracts and 14.5–651.1ppb in 6M HCl acid-vapor-hydrolyzed, hot-water extracts. Amino acids identified in the Apollo soil extracts include glycine, d- and l-alanine, d- and l-aspartic acid, d- and l-glutamic acid, d- and l-serine, l-threonine, and l-valine, all of which had previously been detected in lunar samples, as well as several compounds not previously identified in lunar regoliths: α-aminoisobutyric acid (AIB), d- and l-β-amino-n-butyric acid (β-ABA), dl-α-amino-n-butyric acid, γ-amino-n-butyric acid, β-alanine, and ε-amino-n-caproic acid. We observed an excess of the l enantiomer in most of the detected proteinogenic amino acids, but racemic alanine and racemic β-ABA were present in some samples.