Carbon-rich samples delivered to Earth by NASA’s OSIRIS-REx mission reveal startling intramolecular isotope differences within prebiotic molecules.
Researchers examined a sample of the near-Earth asteroid Bennu, currently located more than 200 million miles away. This pristine extraterrestrial material contains amino acids, which serve as foundational building blocks for proteins on Earth. OSIRIS-REx previously retrieved the sample in 2023.
When scientists analyzed the amino acid beta-alanine, they uncovered unexpected variations. The findings appear in a study titled Nitrogen and intramolecular carbon isotopic measurements of β-alanine in samples from asteroid Bennu and the Murchison meteorite, published in Nature Communications Earth & Environment.
Researchers compared the Bennu sample with beta-alanine extracted from the Murchison meteorite, which fell to Earth in 1969. While bulk carbon isotope averages for both sources appeared nearly identical, their position-specific carbon and nitrogen isotope compositions diverged sharply. This detailed intramolecular view exposes distinct formation environments within the early Solar System.
Specialized analytical hardware made these high-resolution intramolecular measurements possible. The Pennsylvania State University housed unique equipment used to evaluate the rare asteroid material.
Scientists utilized pico-CSIA, standing for Picomolar-scale compound-specific isotope analyses, alongside a modified Gas Chromatography-Orbitrap Mass Spectrometer. “Isotope ratios provide a measurable tag that can link molecules to specific reservoirs or processes,” said co-author Christopher House, professor of geosciences at Penn State.
“I was genuinely gobsmacked by the enormous isotope difference between two neighboring atom positions within the same molecule,” said Katherine Freeman, Professor of Geosciences at Penn State, as reported by Universe Today.
The research team included lead author Ophélie Mcintosh, a former postdoctoral researcher in Penn State’s Department of Geosciences, and co-author Christopher House, professor of geosciences. Mcintosh said that investigating how isotopes distribute inside a molecule helps distinguish between possible formation pathways.
“Instead of simply asking whether a molecule is enriched or depleted in a particular isotope, we can investigate how that isotope is distributed within the molecule and use this pattern to distinguish between possible formation pathways,” Mcintosh said in a press release covered by Penn State.
The preservation of these intramolecular variations indicates that the molecules formed at the very dawn of the Solar System. Freeman said that the compounds might have originated even before Earth formed.
The results demonstrate that the protoplanetary disk was spatially heterogeneous. Organic molecules synthesized through identical chemical routes experienced vastly different local chemical environments.
“One of the main things we discovered, for both glycine and beta-alanine, is that they might have formed in different environments or places in the solar system,” Mcintosh told Universe Today.
These spatial variations suggest that prebiotic chemistry can occur across a wider variety of conditions than previously assumed. Such abiotic baselines aid scientists searching for chemical biosignatures elsewhere in the Solar System, including missions targeting Jupiter’s icy moons.
