When NASA scientists opened the sample return canister from the OSIRIS-REx asteroid sample mission in late 2023, they found something astonishing.
Dust and rock collected from the asteroid Bennu contained many of life’s building blocks , including all five nucleobases used in DNA and RNA, 14 of the 20 amino acids found in proteins, and a rich collection of other organic molecules . These are built primarily from carbon and hydrogen, and they often form the backbone of life’s chemistry.
For decades, scientists have predicted that early asteroids may have delivered the ingredients of life to Earth, and these findings seemed like promising evidence.
Even more surprising, these amino acids from Bennu were split almost evenly between “left-handed” and “right-handed” forms. Amino acids come in two mirror-image configurations, just like our left and right hands, called chiral forms .
On Earth, almost all biology requires the left-handed versions. If scientists had found a strong left-handed excess in Bennu, it would have suggested that life’s molecular asymmetry might have been inherited directly from space. Instead, the near-equal mixture points to a different story: Life’s left-handed preference likely emerged later, through processes on Earth, rather than being pre-imprinted in the material delivered by asteroids.
