First Detection of a Glycine Isomer in the Interstellar Medium

Astronomers have made the first detection of interstellar glycolamide, a molecule closely related to the simplest of the amino acids necessary for life on Earth. Glycolamide is the latest interstellar molecule detected in the G+0.693–0.027 molecular cloud near the center of the Milky Way.

An Elusive Acid

Amino acids are among the most important molecules for life as we know it, providing the means for all life on Earth to build proteins. Beyond Earth, researchers have discovered amino acids in meteorites, comets, and the hot gas surrounding protostars. If amino acids can form in the sparse gas of the interstellar medium, as observations suggest, these critical molecules can be inherited by protoplanetary disks and, eventually, planets themselves.

The simplest of the amino acids necessary for life on Earth is glycine, which contains just 10 atoms. Glycine has been detected in various places in our solar system, but we’ve yet to detect it definitively in the interstellar medium. In a recent article, a research team led by Víctor Rivilla (National Institute of Aerospace Technology–Spanish National Research Council) took the search for interstellar glycine in a new direction by widening the investigation to include its chemical cousins.

Isolating an Isomer

A glycine molecule contains two carbon atoms, two oxygen atoms, five hydrogen atoms, and one nitrogen atom. But there’s more than one way to arrange these atoms into a molecule, and glycine has many isomers: molecules with the same atoms but arranged in a different way. To search for glycine and its isomers, Rivilla and collaborators turned radio telescopes toward G+0.693–0.027, an interstellar molecular cloud near the center of the Milky Way that is already known to host a number of complex organic molecules.

Even in this molecule-rich cloud, glycine remained elusive. However, Rivilla’s team was able to detect one of its isomers for the first time, a molecule called glycolamide, and place upper limits on the abundance of glycine and several of its other isomers.

Tracing Chemical Pathways

Rivilla and collaborators used the measured abundances to explore the likeliest ways glycolamide is created in the interstellar medium. These molecules likely form on the surface of dust grains, where atoms and molecules can gather and link up in the sparse environment of a molecular cloud. For the case of G+0.693–0.027 specifically, ultraviolet photons might create an abundance of highly reactive molecules called radicals, which could interact in this environment to form glycolamide.

And as for glycine? Comparing the abundances of similar molecules suggests that only small amounts of this critical amino acid exist in G+0.693–0.027 — maybe 3–8 times less than the upper limit measured in this study. Given the low abundance, detecting glycine in the interstellar medium will remain difficult with our current instruments.

Citation

“First Glycine Isomer Detected in the Interstellar Medium: Glycolamide (NH₂C(O)CH₂OH),” Víctor M. Rivilla et al 2023 ApJL 953 L20. doi:10.3847/2041-8213/ace977