An international team of researchers has detected a polyheterocyclic organic molecule called hexamethylenetetramine in three carbonaceous meteorites: Murchison, Murray, and Tagish Lake. The presence of this molecule in carbon-rich meteorites promises its pivotal role to carry interstellar prebiotic precursors to the inner Solar System, which should contribute to the chemical evolution in the primordial stage on Earth.
A fragment of the Tagish Lake meteorite. Image credit: Mike Zolensky, NASA’s Johnson Space Center.
Presence of organic molecules in extraterrestrial environments has been widely accepted thanks to recent successes in the detection of cometary molecules toward comet 67P/Churyumov-Gerasimenko, as well as long-standing astronomical observations and analyses of carbonaceous meteorites in laboratories.
However, despite extensive studies on the formation of organic molecules in various extraterrestrial environments such as molecular clouds, protosolar nebula and asteroids, it still remains under debate when, where, and how such extraterrestrial molecules were formed.
A key molecule to solve the problems is hexamethylenetetramine (C6H12N4), also known as hexamine, aminoform, crystamine, methenamine, formin and urotropin.
“By confirming the presence of hexamethylenetetramine in meteorites for the first time, our work supports the hypothesis that the compound was present in asteroids, the parent bodies of many meteorites,” said Dr. Yasuhiro Oba of Hokkaido University and colleagues.
“Early in the Solar System’s history, many asteroids could have been heated by collisions or the decay of radioactive elements.”
“If some asteroids were warm enough and had liquid water, hexamethylenetetramine could have broken down to provide building blocks that in turn reacted to make other important biological molecules which have been found in meteorites, including amino acids.”
“Some types of amino acids are used by life to make proteins, which are used to build structures like hair and nails, or to speed up and regulate chemical reactions.”
“While the diversity of organic compounds in meteorites is well-documented, many questions remain about the processes by which these compounds were formed.”
“The most important meteorites in this area of research are carbonaceous chondrites, stony meteorites that contain high percentages of water and organic compounds.”
The scientists developed a method that specifically extracted hexamethylenetetramine from meteorites with minimal degradation.
They were able to isolate significant quantities of hexamethylenetetramine and its derivatives from Murchison, Murray and Tagish Lake carbonaceous chondrites.
They also examined the role hexamethylenetetramine derivatives may have played in the formation of amino acids in meteorites.
“While we were unable to make definitive conclusions in this study, the discovery of hexamethylenetetramine and its derivatives in these meteorites will lead to future experiments to understand the origin and chemical formation processes of amino acids and other prebiotic compounds in extraterrestrial environments,” the authors said.
The results were published in the journal Nature Communications.
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Y. Oba et al. 2020. Extraterrestrial hexamethylenetetramine in meteorites — a precursor of prebiotic chemistry in the inner Solar System. Nat Commun 11, 6243; doi: 10.1038/s41467-020-20038-x
