Biological Homochirality and the Search for Extraterrestrial Biosignatures

TL;DR

This paper reviews three potential mechanisms behind biological homochirality, discussing their implications for astrobiology and how they could be tested through observations of extraterrestrial environments.

Contribution

It provides a comparative analysis of three hypotheses for the origin of homochirality and explores their observational consequences for detecting biosignatures beyond Earth.

Findings

Different mechanisms predict distinct enantiomeric excess signatures.

Observations of extraterrestrial molecules could distinguish among hypotheses.

Understanding homochirality aids in identifying extraterrestrial life biosignatures.

Abstract

Most amino acids and sugars molecules occur in mirror, or chiral, images of each other, knowns as enantiomers. However, life on Earth is mostly homochiral: proteins contain almost exclusively L-amino acids, while only D-sugars appear in RNA and DNA. The mechanism behind this fundamental asymmetry of life remains unknown, despite much progress in the theoretical and experimental understanding of homochirality in the past decades. We review three potential mechanisms for the emergence of biological homochirality on primal Earth and explore their implications for astrobiology: the first, that biological homochirality is a stochastic process driven by local environmental fluctuations; the second, that it is driven by circularly-polarized ultraviolet radiation in star-forming regions; and the third, that it is driven by parity violation at the elementary particle level. We argue that each of these mechanisms leads to different observational consequences for the existence of enantiomeric excesses in our solar system and in exoplanets, pointing to the possibility that the search for life elsewhere will help elucidate the origins of homochirality on Earth.