Detecting Fundamental Chiral Biosignatures in the Ultraviolet Polarization Spectrum

Abstract

Chiral molecules are ubiquitous and necessary for life as we know it. In extant life, the amino acid and sugar constituents of proteins and biopolymers consist of only one enantiomer. This “homochirality” is plausibly generic to any biochemical life and therefore may represent a pure, agnostic biosignature. The ultraviolet (UV) circular polarization spectrum offers a practical method for detecting chirality for generic biomass and hence can be a powerful tool for detecting such biosignatures in an extraterrestrial setting. Here, we demonstrate distinctive UV chiral signatures from astrobiology mission-relevant chemoautotrophic microbes when measured in transmission spectroscopy. Polarization and spectral absorption features are strongly evident at wavelengths expected for protein secondary structures and other chiral molecules, even though the microbial samples are not expected to have survived the study environment. When measured with reflection spectropolarimetry, which would be required for a remote sensing observation, we obtained only null results. Following 10 keV electron irradiation in the Minos chamber at the Jet Propulsion Laboratory Ocean Worlds Laboratory, which is equivalent to exposure of approximately 1 month on the Europan surface in a region where radiation is most intense, chiral signatures persisted to a degree dependent on sample thickness and composition. A control measurement of a Murchison meteorite sample was also undertaken.