Nitriles, a class of organic molecules with a cyano group—a carbon atom bound by an unsaturated triple bond to a nitrogen atom—are typically toxic. But paradoxically, they are also a pivotal precursor to the molecules necessary for life, such as ribonucleotides, made up of the nucleobases or “letters” A, U, C, and G joined to form ribose and phosphate groups, which together make up RNA. Now a team of researchers from Spain, Japan, Chile, Italy, and the US shows that a wide variety of nitriles occur in interstellar space in the G+0.693-0.027 molecular cloud near the center of the Milky Way.
Dr. Víctor M. Rivilla, a researcher at the Center for Astrobiology of the Spanish National Research Council (CSIC) and the National Institute of Aerospace Technology (INTA) in Madrid, Spain, and the first author of the new study published in Frontiers in Astronomy and Space Sciences, said: “Here we show that the chemistry that takes place in the interstellar medium is capable of efficiently forming multiple nitriles, which are the key molecular precursors of the ‘RNA World’ scenario.”
A possible “RNA only” world.
According to this scenario, life on Earth was initially based on only RNA and DNA, and protein enzymes evolved later. RNA can both store and copy information like DNA and catalyze reactions like enzymes. According to the “RNA World” theory, nitriles and other building blocks for life did not necessarily all originate on Earth itself: they could also have formed in space and “hitchhiked” to the young Earth inside meteorites and comets during the “Late Period of Heavy Bombardment between 4.1 and 3, 8 billion years. In support of this, nitriles and other precursor molecules for nucleotides, lipids, and amino acids have been found inside contemporary comets and meteors.
But where in the universe could these molecules have come from? Primary candidates are molecular clouds, dense and cold regions of the interstellar medium suitable for forming complex molecules. For example, the molecular cloud G+0.693-0.027 has a temperature of around 100 K and is about three light-years across, with a mass about a thousand times that of our Sun. There is no evidence that stars are currently forming inside G+0.693-0.027, although scientists hypothesize that it could develop into a stellar nursery in the future.
“The chemical content of G+0.693-0.027 is similar to that of other star-forming regions in our galaxy, as well as that of Solar System objects such as comets. This means that its study can provide us with important insights into the chemical components that were available in the nebula , which gave rise to our planetary system,” explained Rivilla.