Scientists have detected tryptophan in asteroid Bennu samples, completing 15 of the 20 amino acids essential to life
A paper published near Thanksgiving 2025 reported tryptophan in material returned by NASA's OSIRIS-REx mission, the first time the amino acid has been found in any extraterrestrial sample. The finding is pending reproduction, but it extends a remarkable inventory of life's chemical building blocks found on a single asteroid.
Researchers analyzing material returned from asteroid Bennu have detected tryptophan, bringing the count of life-essential amino acids found in those samples to 15 of the canonical 20. Harold Connolly Jr., a scientist involved in the OSIRIS-REx mission sample analysis, describes the result as significant but still requiring confirmation.
The headline finding that had circulated before this result was already striking: 14 of the 20 amino acids required for life, present in a single asteroid sample. Connolly describes the 15th detection as coming from a paper by Mahar Edall published in November, timed, as he notes, right near Thanksgiving. “It’s probably 15 because a paper by Mahar Edall that came out in November found the 15th one and we have to reproduce it, but that was right near Thanksgiving and that 15th one was tryptophan.”
The external record supports the claim. Research published in the Proceedings of the National Academy of Sciences, with corroborating coverage from the University of Arizona and NASA, confirms that tryptophan was detected in Bennu samples returned by the OSIRIS-REx mission, with findings emerging around late November 2025. According to those sources, it marks the first detection of tryptophan in any extraterrestrial sample ever analyzed.
And indeed they have found that the main headlines is you know 14 of the 20 amino acids that are needed for life but really it's probably 15 because a paper by Mahar Edall that came out uh in November found the 15th one and we have to reproduce it but that was right near Thanksgiving and that 15th one was tryptophan Harold Connolly Jr.
Tryptophan is not a minor entry on the list. It is one of the amino acids humans cannot synthesize internally and must obtain from diet. Its presence in a carbonaceous asteroid sample strengthens the hypothesis that the chemical precursors of biology were delivered to early Earth from space, a process known as exogenous delivery. Finding it in Bennu material is a different order of result from finding simpler amino acids such as glycine, which have appeared in meteorites for decades.
The caveat Connolly attaches matters. Reproduction is the standard the result must meet before it is treated as settled. A single detection, however well-instrumented, can reflect contamination, instrumental artifact, or a sample anomaly that does not hold when a second team runs independent analysis on a separate aliquot. The OSIRIS-REx sample archive exists precisely to enable that work: NASA distributed portions of the Bennu material to multiple research groups so that findings can be checked against independent preparations.
What makes the Bennu inventory unusual is its breadth rather than any single detection. Meteorite analyses have found amino acids before, but the range and quantity found in pristine, contamination-controlled asteroid material returned by a dedicated spacecraft is a different class of evidence. The controlled collection and curation of the sample reduces the contamination explanations that have long complicated meteorite studies.
If the tryptophan result is reproduced, the Bennu sample will have yielded 15 of the 20 amino acids that living systems use to build proteins. The remaining five become, in that scenario, the next target. Whether they are absent from Bennu, present below current detection limits, or simply not yet analyzed depends on work still in progress. The science is not complete, but the direction it is pointing has not changed since the first Bennu samples were opened.