New research discovers that molecular clouds are loaded with key precursors for life on Earth. This image is from the molecular cloud “Pigtail”. Credit: Keio University, NAOJ
Key precursors of life on Earth are abundant in interstellar molecular clouds and could have reached Earth within comets and meteors.
Nitriles, a class of organic molecules with a cyano group (a carbon atom attached to an unsaturated triple bond to a nitrogen atom) are typically toxic. But, paradoxically, they are also a key precursor of molecules essential for life on Earth, such as ribonucleotides, composed of nucleobases or ‘letters’ A, U, C and G attached to a group of ribose and phosphate, which in together they form RNA. . Now, a team of scientists from Spain, Japan, Chile, Italy and the United States show that a wide range of nitriles is produced in interstellar space within the molecular cloud G + 0.693-0.027, which is located near the center of the Milky Way. galaxy.
“Here we show that chemistry that takes place in the interstellar medium is capable of efficiently forming multiple nitriles, which are key molecular precursors of the ‘RNA World’ scenario,” said Dr. Victor M. Rivilla, a researcher at Center for Astrobiology of the Consejo Superior de Investigaciones Científicas (CSIC) and the Instituto Nacional de Tecnología Aerospace (INTA) in Madrid, Spain, and first author of the new study.
Research shows that a wide range of nitriles occurs in interstellar space within the molecular cloud G + 0.693-0.027, which is located near the center of the Milky Way. Credit: Pablo Carlos Budassi
Possible “RNA only” world.
Under this scenario, life on Earth was originally based solely on RNA, and protein enzymes and DNA later evolved. RNA can perform both functions: catalyze reactions such as enzymes, and store and copy information such as DNA. According to the “RNA World” theory, nitriles and other basic elements of life did not necessarily arise on Earth itself: they could also have originated in space and “hitchhiked” the young Earth inside. of comets and meteorites during the “Late Heavy”. Bombing period, between 4.1 and 3.8 billion years ago. In support, nitriles and other nucleotide, lipid, and amino acid precursor molecules have been found within contemporary meteors and comets.
Where could these molecules have come into space? The main candidates are molecular clouds, which are dense, cold regions of the interstellar medium, and are suitable for the formation of complex molecules. For example, the molecular cloud G + 0.693-0.027 has a temperature of about 100 K and is about three light-years in diameter, with a mass about a thousand times that of our Sun. Although scientists suspect it could evolve to become a stellar nursery in the future, there is no evidence that stars are currently forming within G + 0.693-0.027.
“The chemical content of G + 0.693-0.027 is similar to that of other star-forming regions of our galaxy, and also to that of objects in the solar system such as comets. This means that their study can give us insights. important about the chemical ingredients that were available in the nebula that give rise to our planetary system, ”Rivilla explained.
Electromagnetic spectra studied
Rivilla and his colleagues used two telescopes in Spain to study the electromagnetic spectra emitted by G + 0.693-0.027: the IRAM telescope 30 meters wide in Granada and the Yebes telescope 40 meters wide in Guadalajara. They detected the nitriles cyanoallene (CH2CCHCN), propargyl cyanide (HCCCH2CN) and cyanopropium, which had not yet been found at G + 0.693-0.027, although they had been reported in 2019 in the dark cloud TMC-1 in the constellations Taurus. and Auriga, a molecular cloud with very different conditions from G + 0.693-0.027.
Rivilla et al. also found possible evidence of the appearance at G + 0.693-0.027 of cyanoformaldehyde (HCOCN) and glycolinitrile (HOCH2CN). Cyanoformaldehyde was first detected in the molecular clouds TMC-1 and Sgr B2 in the constellation Sagittarius, and glycolinitrile in the Sun-like protostar IRAS16293-2422 B in the constellation Ophiuchus.
Other recent studies have also reported other RNA precursors within G + 0.693-0.027, such as glycolaldehyde (HCOCH2OH), urea (NH2CONH2), hydroxylamine (NH2OH), and 1,2-etenediol (C2H4O2), confirming that the Interstellar chemistry is able to provide the most basic ingredients for the “RNA World.”
Nitriles among the most abundant chemical families in space
The final author, Dr. Miguel A Requena-Torres, a professor at Towson University in Maryland, USA, concluded: “Thanks to our observations over the past few years, including current results, we now know that nitriles are found. among the most abundant chemical families in the universe. We have found them in molecular clouds in the center of our galaxy, protostars of different masses, meteorites and comets, and also in the atmosphere of Titan, Saturn’s largest moon. ” .
The second author, Dr. Izaskun Jiménez-Serra, also a researcher at the CSIC and the INTA, looked ahead: “So far we have detected several simple precursors of ribonucleotides, the building blocks of RNA. But there are still key molecules that are missing that are hard to spot. For example, we know that the origin of life on Earth probably also required other molecules such as lipids, which are responsible for the formation of the first cells. Therefore, we should also focus on understanding how lipids could be formed from simpler precursors available in the interstellar medium. “
Reference: “Molecular precursors of the RNA-world in space: new nitriles in the G + 0.693-0.027 molecular cloud” July 8, 2022, Frontiers in Astronomy and Space Sciences.DOI: 10.3389 / fspas.2022.876870