Amino acids - the molecules from which proteins are built - have been found both in samples of the asteroid Bennu delivered to Earth in 2023 by NASA's OSIRIS-REx mission and in the Murchison meteorite, which fell in 1969. A new study published in the journal Communications Earth & Environment has shown that these molecules could have formed through the same process, but in different parts of the Solar System.
A team led by scientists from the University of Pennsylvania (USA) studied the amino acids using isotope analysis - varieties of atoms of the same element with different masses. The ratio of isotopes works as a label indicating which chemical "reservoirs" or conditions the atoms originated from. Two instruments were used for this, one of which exists only at the University of Pennsylvania and makes it possible to measure the isotopic composition of tiny amounts of material.
Particular interest was drawn by beta-alanine - an amino acid that is not among the 20 standard "building blocks" of proteins but is produced in the human body and can take part in the formation of peptides. It is especially abundant in space samples, which makes it a convenient model for studying prebiotic chemistry - the chemistry of compounds that preceded the emergence of life.
The main surprise came from the distribution of carbon isotopes within the molecule itself. If the values are averaged across the whole molecule, the Bennu and Murchison samples look almost identical. But when each carbon atom was analyzed separately, the picture turned out to be completely different. One of the three carbon atoms in beta-alanine carried an unusually high share of heavy isotopes, while the other two were depleted in them. Moreover, the enriched carbon in the Bennu sample showed the strongest isotopic anomaly ever recorded in an organic molecule of cosmic origin.
According to the authors, this pattern of isotopic labels indicates that the Bennu and Murchison molecules could have arisen as a result of similar chemical processes, but in different regions of the Solar System. This broadens understanding of where compounds important for prebiotic chemistry could have formed.
The same group previously studied the simplest amino acid, glycine, and concluded that on Bennu it could have formed in a cold and harsh environment - contrary to the widespread idea that warm and wet conditions are essential for the emergence of the "building blocks of life."
The scientists emphasize that this concerns the chemical pathways by which molecules form, not proof of the origin of life. The next step is to find out how exposure to space, for example contact with water, affects the order of isotopes within molecules. The researchers also hope that the method of intramolecular isotope analysis will find applications beyond astronomy.