Researchers analyzed stable isotopes of carbon and nitrogen in samples from the asteroid Bennu. Isotopes are atoms of the same element with different numbers of neutrons. The ratios between them serve as a chemical “fingerprint.” They can indicate whether a molecule formed in liquid water, ice, or other conditions.
For years, scientists have sought an answer to a seemingly simple question: Where did basic organic molecules form before life began on Earth?
One of the leading candidates is the family of amino acids, the building blocks of proteins. Now, a new analysis of asteroid samples returned to Earth is providing a direct glimpse into the chemistry of the early solar system, rather than relying on indirect clues from meteorites that landed here long ago.
The samples were collected from a near-Earth asteroid called Bennu. They arrived on Earth in 2023 and were tested using highly sensitive measurement methods. The advantage of such samples is that they are better preserved than meteorites because they are collected and sealed under more controlled conditions. This reduces the chance that contamination or environmental changes on Earth could affect the results.
What did they find in the sample, and what was particularly “unusual”?
The study focused not only on the question of which amino acids exist, but also on how they were formed. To find the answer, the researchers analyzed stable isotopes of carbon and nitrogen. Isotopes are atoms of the same element, with different numbers of neutrons. The ratio of them serves as a chemical “fingerprint.” They can indicate whether a molecule formed in liquid water, ice, or other conditions.
Among other things, isotopic signatures of glycine, the simplest amino acid, were measured. This is a particularly challenging measurement when the quantities are tiny. Here, another step was taken. The researchers did not settle for an “average” measurement of the molecule, but also examined patterns within that molecule, that is, how the carbon isotopes are distributed between different parts of it. The comparison with a well-known meteorite called Murchison showed different signatures. This means that the glycine in the samples and the glycine in the meteorite were not necessarily formed by the same chemical pathway.
Some of the data indicated a very high enrichment of “heavy” nitrogen in certain amino acids. Such enrichment may be consistent with reactions occurring in a very cold environment, where ice, radiation, and extreme processes play a major role. The researchers suggested that at least some of the organic matter formed under frosty conditions in the early solar system, and not just under warm conditions where water was liquid, as is sometimes shown.
Why is this important, and what is still unclear?
If the building blocks of life can form even in extreme cold, it greatly expands the “map of possibilities” in the solar system and beyond. It means that an environment with stable liquid water does not have to exist to have rich pre-biological chemistry. Such a scenario fits the idea that organic materials could have formed far from the sun, been preserved in ice, and only later reached more interior regions, including the young Earth.
However, the study also highlights the complexity. In some molecules, isotopic differences were found between two chemical mirror images, which is not obvious. That is, even when it comes to the same chemical formula, a “right-handed” and a “left-handed” structure can carry different signatures. This is a mystery that suggests a rich chemical history, and perhaps a combination of more than one formation pathway.
The bottom line is that the samples provide direct evidence that the chemistry of the early solar system was more diverse than previously thought. Amino acids may have formed through a combination of processes: some in water, some in ice, and some in transition between the two. In future research, the measurements will be extended to additional molecules and an attempt will be made to recreate possible pathways in the laboratory under cold and radiation conditions similar to those of the “primordial environment” beyond the snow line.
More of the topic in Hayadan:
