Scientists find evidence that an asteroid contains tryptophan

Tryptophan, the essential amino acid behind the Thanksgiving myth that eating turkey can make you sleepy, has been found to exist on Bennu, a small asteroid that swings by our planet about every six years.

The discovery stems from an unprecedented sample collected by NASA’s OSIRIS-REx mission, which landed a spacecraft on the asteroid in 2020, captured 4.3 ounces (121.6 grams) of rocks and dust, and safely returned the cache to Earth in 2023. NASA has since distributed a small portion of that sample to researchers around the world to be analyzed.

Studying Bennu is important because its composition reflects that of the early solar system, giving scientists a glimpse into the beginnings of life. Previous research on Bennu samples had already found 14 of the 20 amino acids all living organisms on Earth stem from, as well as all five biological nucleobases — the components that make up the genetic code in DNA and RNA.

Researchers also previously detected amino acids in samples from another asteroid, Ryugu, which the Japan Aerospace Exploration Agency collected in 2019, as well as in various meteorites that have fallen to Earth. This growing body of evidence suggests that asteroids might have delivered essential life ingredients to our planet early on, according to experts.

Now, a new analysis of Bennu samples has confidently, although not yet conclusively, identified tryptophan, increasing the tally of protein-building amino acids in the asteroid to 15 out of 20.

The presence of tryptophan in an asteroid supports the idea that the recipe for life might not have begun only on Earth, Aponte added in an email: “Seeing it form naturally in space tells us that these ingredients were already being made out in the early Solar System. That would have made it easier for life to get started.”