The origins of the building blocks of life may be more widespread than we realize, according to new findings from asteroid samples brought back to Earth from the space rock Bennu by NASA’s OSIRIS-REx mission.
At least 14 of the 20 amino acids used by living organisms earthand 19 other amino acids not used by life, has been identified With a sample from bennedelivered to Earth in September 2023. These amino acids were thought to have formed in warm, water-rich conditions near the sun, which formed 4.5 billion years ago.
“This confirms that the building blocks of life can form in diverse environments throughout the universe,” Alison Baczynski, an organic chemist at Pennsylvania State University and co-lead author of the new study, told Space.com.
Budzynski led a team that investigated the isotopic composition of Bennu’s amino acids, focusing on glycine, the simplest amino acid in the sample. On Earth, glycine is produced when hydrogen cyanide, ammonia, and organic compounds called aldehydes react in warm water. Budzynski’s team used Murchison. meteorite For reference, the one that fell in Australia in 1969. The amino acids found at Murchison have an isotopic composition that suggests they were formed in this way.
On the other hand, Benne’s glycine and other amino acids present have a different isotopic composition than the Murchison amino acids. Instead, their isotopic composition is consistent with what would be expected given that they formed in a chemically distinct, frozen environment far from the sun, while still being influenced by the solar ultraviolet radiation needed to trigger the reactions that form amino acids.
“It was really exciting that Bennu’s amino acids showed a very different isotope pattern than Murchison’s. This suggests that the amino acids were formed by different routes and in different regions.” solar system” Budzynski said.
The early solar system, when planets were still forming, was divided by a dividing line known as the “snow line.” Beyond the snow line, water is frozen, but inside the snow line, water exists as a liquid or vapor. Chemical reactions proceed differently depending on which side of the snow line they occur.
It is not entirely clear whether the amino acids formed across the snow line on icy dust grains, then migrated inward and were accreted by Bennu’s parent body (which was shattered by an impact at some point in its past, and Bennu is a large fragment of it), or whether Bennu’s parent body itself formed beyond the snow line. However, evidence indicates that the latter is likely the origin.
“Our isotopic data indicate that the amino acids formed in a cold, icy environment, and other data obtained by the OSIRIS-REX mission suggests that Bennu’s parent body formed beyond the snowline,” Budzynski said.
As part of the analysis of the isotopic composition of Bennu’s amino acids, new mysteries have also been uncovered. Amino acids come in two forms, left-handed or right-handed, depending on how their molecular structure is mirrored. For reasons not yet understood by scientists, all life on Earth uses left-handed amino acids.
Scientists used to think that for certain types of amino acids, left-handed and right-handed types were otherwise identical. However, analysis of one of the amino acids in Bennu’s samples, glutamic acid, revealed that left-handed and right-handed individuals have different nitrogen isotopes. Why they need to be different is a mystery, and glutamate is not one of the amino acids that life uses, but the question is whether this has anything to do with why life only uses left-handed amino acids.
“Nitrogen isotope values have been thought to be the same in both forms, so it was surprising to find that even though Bennu had equal proportions of L-glutamate and D-glutamate, the nitrogen isotope values were very different,” said Budzynski. “This is one of the most interesting findings and we are excited to investigate this further.”
The discovery that amino acids can be formed in more ways than we thought gives a further boost to the search for life beyond Earth. When the building blocks of life form in a variety of conditions, the number of potential locations in which life can be found increases.
The results of this study were published in the journal February 9th. Proceedings of the National Academy of Sciences.