  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.
