Biological Homochirality And The Search for Extraterrestrial Biosignatures

By Keith Cowing
May 3, 2022
Filed under
Biological Homochirality And The Search for Extraterrestrial Biosignatures
Evolution of 2d chiral domains. Red (+1 on the color bar) corresponds to the L-phase and blue (-1 on the color bar) corresponds to the D-phase. Time runs from left to right and top to bottom. Top left, the near-racemic initial conditions. Top mid and top right, evolution of the two percolating chiral domains separated by a thin domain wall. Bottom left, environmental effects break the stability of the domain wall network. Bottom right, subsequent surface-tension driven evolution leads to a enantiomerically-pure world [21].

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.

Marcelo Gleiser

Comments: arXiv admin note: text overlap with arXiv:0802.1446
Subjects: Earth and Planetary Astrophysics (astro-ph.EP); Biological Physics (; Biomolecules (q-bio.BM)
Cite as: arXiv:2205.01193 [astro-ph.EP] (or arXiv:2205.01193v1 [astro-ph.EP] for this version)
Submission history
From: Marcelo Gleiser
[v1] Mon, 2 May 2022 20:14:17 UTC (1,446 KB)
Astrobiology, Astrochemistry

SpaceRef co-founder, Explorers Club Fellow, ex-NASA, Away Teams, Journalist, Space & Astrobiology, Lapsed climber.