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Allison A. Baczynski, Ophélie McIntosh, Danielle N. Simkus | Proceedings of the National Academy of Sciences | (2026)
Primary Link Pubmed DOI Openalex Full text (OA)

Abstract

Samples collected from the carbonaceous near-Earth asteroid Bennu and delivered to Earth by NASA's OSIRIS-REx mission contain organic molecules relevant to prebiotic chemistry. Stable isotopic measurements of extraterrestrial soluble organic matter provide critical insights into the formation pathways and alteration histories of such molecules, which hold significance for understanding the origins of life. We leverage state-of-the-art techniques for picomolar-scale isotopic analyses of amino acids in samples of Bennu and, for comparison, the carbonaceous meteorite Murchison. We report intramolecular δ<sup>13</sup>C values for glycine, which have not previously been measured in extraterrestrial materials; molecular-averaged δ<sup>13</sup>C values for amino acids, aldehydes, and ketones; and δ<sup>15</sup>N values for glycine, β-alanine, and D/L-glutamic acid. Intramolecular carbon isotope patterns of glycine in Bennu contrast with those in Murchison, suggesting distinct formation pathways. We explore several formation mechanisms and hypothesize that the observed glycine in Murchison formed dominantly by a Strecker-like synthesis under aqueous conditions, whereas the glycine currently found in Bennu may have formed mainly by modified radical-radical reactions in primordial ices at the cold, outer reaches of the early Solar System and retained its isotopic values throughout accretion and multiple episodes of aqueous alteration. This hypothesis is supported by the highly <sup>15</sup>N-enriched δ<sup>15</sup>N values in Bennu amino acids (+170 to 277‰). Differences in the δ<sup>15</sup>N values of D- and L-glutamic acid (Δ = 87‰) in Bennu affirm published reports of enantiomeric differences in meteoritic amino acids and challenge the assumption of isotopic uniformity between amino acid chiral pairs.

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Plain English Takeaway

Scientists studied tiny pieces from asteroid Bennu and found that the building blocks of life, like amino acids, can form in more than one way in space.

Study Aim

The paper aims to determine how amino acids (the basic components of proteins) formed in the early Solar System by analyzing the carbon and nitrogen isotopes (different forms of the same element) in samples from asteroid Bennu. The researchers want to compare these results with those from the well-known Murchison meteorite to understand if different chemical processes created these molecules in different places or times. Simply put: The study wants to find out how life's building blocks formed in space by looking at their chemical fingerprints.

Study Design

The researchers used advanced techniques to measure very small amounts of carbon and nitrogen isotopes in amino acids from Bennu samples collected by NASA's OSIRIS-REx mission. They also analyzed similar molecules from the Murchison meteorite for comparison. The team measured isotope values within individual molecules and across different types of molecules, focusing on glycine, β-alanine, and both forms (D and L) of glutamic acid. This approach allowed them to identify differences in how these molecules formed and changed over time. Simply put: The scientists compared the chemical makeup of molecules from Bennu and a meteorite to see how they were made.

Findings

The study reveals that the carbon and nitrogen isotope patterns in Bennu's amino acids are different from those in the Murchison meteorite. The authors argue that glycine in Murchison likely formed in water through a process called Strecker synthesis, while glycine in Bennu probably formed in very cold ices far from the Sun, using a different chemical reaction. The research demonstrates that Bennu's amino acids have unusually high nitrogen-15 values, supporting the idea of a unique formation environment. The findings also show that the two mirror-image forms of glutamic acid in Bennu have different nitrogen isotope values, challenging the assumption that such pairs are always chemically identical. These results suggest that multiple chemical pathways created amino acids in the early Solar System, which could have influenced the origins of life on Earth. Simply put: The study found that life's building blocks formed in different ways in space, depending on where and how they were made.

Referenced In

StarTalk

Season 17, Episode 22: Asteroid Bennu and the Origin of Life in the Solar System

Hey StarTalkians! Neil and Chuck sat down with Professor Harold Connolly Jr. for season 17, episode 22, talking about his work on the OSIRIS-Rex mission and the asteroid Bennu. After covering the basics of the mission, they briefly discussed what it could mean for the origin of life in the solar system: 

Secrets of Asteroid Bennu with Harold Connolly Jr. - StarTalk Radio

(From 53:55)

The discussion touches on the “panspermia” hypothesis. The overall idea is unlikely, to say the least, but a limited form of it could be more promising.

What They Found on Bennu

As Professor Connolly explains in the podcast, the asteroid Bennu contained a lot of organic materials.

One paper he co-authored describes what they found on the carbon-rich asteroid. Most importantly, this included 14 out of 20 terrestrial amino acids, the building blocks of life. Interestingly, these may have been formed in low-temperature reactions involving ammonia ice, unlike previous cases that depended on mild temperatures and liquid water.

Another paper added a 15th terrestrial amino acid, noting that such prebiotic molecules could have been deposited onto the young Earth by asteroid impacts.

The Panspermia Hypothesis

This leads into Chuck’s question about “lithopanspermia,” a variant of the panspermia hypothesis. This is the idea that the earliest forms of life may have developed away from the Earth, eventually being delivered to our planet by asteroid impact events (hence “litho”) and evolving terrestrially.

This hypothesis isn’t super likely, though. After all, could life really survive the journey through space and the impact itself? And the whole thing requires extra-terrestrial life to exist in the first place.

Pseudo-lithopanspermia – A Viable Alternative?                              

Instead of living microbes making the unlikely journey through space, the more likely “pseudo-panspermia” hypothesis posits that prebiotic organic molecules arrived on Earth that way. If this came from an asteroid like Bennu, we might call this “pseudo-lithopanspermia.”

Professor Connolly’s research shows that such molecules certainly exist. Additionally, modelling suggests that plenty of material from other bodies ends up on Earth – including 21 million landing from Mars alone over 3.5 billion years.

This removes a lot of problems with panspermia, and it’s definitely an interesting possibility. However, Neil’s point in the podcast pours cold water ammonia over this: why would we need extra-terrestrial amino acids if they seem to form everywhere anyway?

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