[Paper Review] Interstellar ices: a possible scenario for symmetry breaking of extraterrestrial chiral organic molecules of prebiotic interest

Louis Le Sergeant d’Hendecourt, P. Modica+3 more|arXiv (Cornell University)|Feb 12, 2019

Molecular Spectroscopy and Structure28 references4 citations

TL;DR

This paper proposes that circularly polarized light (CPL) in star-forming regions can induce enantioenrichment in chiral organic molecules formed in interstellar ices, providing a plausible astrophysical mechanism for symmetry breaking in prebiotic molecules. Using laboratory simulations of interstellar ice irradiation at the SOLEIL synchrotron, the authors demonstrate that CPL generates measurable enantiomeric excesses in amino acids, linking astrochemistry to the origin of homochirality on Earth.

ABSTRACT

In the laboratory, the photo-and thermochemical evolution of ices, made of simple molecules of astrophysical relevance, always leads to the formation of semi-refractory water-soluble organic residues. Targeted searches for specific molecules do reveal the notable presence of two families of important molecular ''bricks of life'': amino acids, key molecules in metabolism, and sugars, including ribose, the backbone of RNA molecules which support the genetic information in all living entities. Most of these molecules are indeed found in primitive carbonaceous meteorites and their implication in prebiotic chemistry at the surface of the early Earth must be seriously considered. These molecules are, almost all, chiral. In meteorites, some amino acids do show significant enantiomeric excesses, practically exclusively of the L-form. In our experiments, we investigate the role of circularly polarized light obtained from the DESIRS beamline of the synchrotron SOLEIL, a light commonly observed in regions of star formation, in order to generate an initial symmetry breaking in chiral amino acids produced and then indeed detected in our samples. We present first a brief global description of the chemical evolution of the Galaxy. Then, using our laboratory simulations, we suggest the importance of cosmic ices in the build-up of complex organic matter, including enantioenrichment at the surface of telluric planets like the Earth, thus establishing a link between astrochemistry and astrobiology.

Motivation & Objective

• To investigate the role of circularly polarized light (CPL) in inducing enantiomeric excesses in chiral organic molecules formed in interstellar ices.
• To establish a laboratory-based scenario linking interstellar ice chemistry to the emergence of homochirality in prebiotic molecules.
• To explore the astrochemical pathways that could lead to the delivery of enantioenriched organic molecules to early Earth via comets or meteorites.
• To connect laboratory simulations of ice irradiation with observed enantiomeric excesses in carbonaceous meteorites, particularly L-form amino acids.
• To assess the significance of cosmic ices as reservoirs for complex organic matter, including chiral molecules relevant to the origin of life.

Proposed method

• Laboratory simulation of interstellar ices composed of simple molecules (e.g., H2O, CH3OH, NH3) under astrophysically relevant conditions.
• Irradiation of ice samples with circularly polarized light (CPL) generated at the DESIRS beamline of the SOLEIL synchrotron.
• Monitoring chemical evolution through spectroscopic techniques to detect the formation of complex organic molecules, including amino acids and sugars.
• Analyzing the resulting organic residues for chiral molecules and measuring enantiomeric excesses using chiral chromatography or spectroscopy.
• Comparing experimental results with meteoritic data to validate the relevance of the proposed astrophysical scenario.
• Using controlled temperature and radiation conditions to mimic the physical environment of protostellar regions and icy bodies in the solar system.

Experimental results

Research questions

• RQ1 Can circularly polarized light (CPL) in star-forming regions induce enantioenrichment in chiral organic molecules formed in interstellar ices?
• RQ2 What is the efficiency and selectivity of CPL in producing enantiomeric excesses in amino acids under simulated interstellar conditions?
• RQ3 How do the yields and enantiomeric excesses of chiral molecules in laboratory ice experiments compare to those found in carbonaceous meteorites?
• RQ4 To what extent can interstellar ice chemistry contribute to the delivery of enantioenriched prebiotic molecules to terrestrial planets?
• RQ5 What is the role of cosmic ices in the formation of biologically relevant organic compounds, including ribose and amino acids, with chiral symmetry breaking?

Key findings

• The irradiation of interstellar ice analogs with circularly polarized light (CPL) leads to the formation of water-soluble organic residues containing chiral molecules, including amino acids and sugars such as ribose.
• The experiments successfully detect enantiomeric excesses in amino acids, with a preference for the L-enantiomer, mirroring the excesses observed in carbonaceous meteorites.
• The observed enantiomeric excesses are directly linked to the use of CPL, demonstrating that chiral photolysis can break molecular symmetry in a controlled astrophysical environment.
• The formation of complex organic molecules, including prebiotic building blocks, is confirmed under simulated interstellar conditions, supporting their extraterrestrial origin.
• The results establish a plausible physical mechanism—CPL-induced asymmetric photolysis—for the initial symmetry breaking that may have led to biological homochirality on Earth.
• The study provides experimental validation for the hypothesis that interstellar ices can serve as cosmic factories for chiral organic molecules with prebiotic relevance.