Most amino acids and sugar 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.

大多数氨基酸和糖分子以彼此的镜像或手性图像出现，称为对映体。然而，地球上的生命大多是纯手性的：蛋白质几乎只含有 L-氨基酸，而 RNA 和 DNA 中只含有 D-糖。尽管过去几十年来对同手性的理论和实验理解取得了很大进展，但这种生命基本不对称性背后的机制仍然未知。我们回顾了原始地球上生物同手性出现的三种潜在机制，并探讨了它们对天体生物学的影响：第一，生物同手性是由当地环境波动驱动的随机过程；第二，它是由恒星形成区域的圆偏振紫外线辐射驱动的；第三，它是由基本粒子层面的宇称破坏驱动的。我们认为，这些机制中的每一种都会导致对太阳系和系外行星中对映体过量存在的不同观测结果，指出在其他地方寻找生命将有助于阐明地球上同手性起源的可能性。