A team of researchers from Spain, Japan, Chile, Italy and the United States recently discovered that a wide range of nitriles occur in interstellar space within the molecular cloud G+0.693-0.027, near the center of the Milky Way. They showed that chemistry taking place in the interstellar medium can efficiently form multiple nitriles, which are critical molecular precursors of the ‘RNA World’ scenario.
One of the most supported hypotheses for the origin of life is known as the RNA world, in which RNA could have played both metabolic and genetic roles. This theory suggests that nitriles and other building blocks for life need not necessarily have arisen on Earth itself: they may also have originated in space and “hitchhiked” to young Earth inside meteorites and comets during the ” Late Heavy Bombardment”, between 4.1 and 3.8 billion years ago. Nitriles and other precursor molecules of nucleotides, lipids and amino acids were discovered inside modern comets and meteors, which gives this claim.
But where in space would these molecules have come from?
Molecular clouds are the prime suspect. These clouds are cold, dense areas of the interstellar medium. For example, the molecular cloud G+0.693-0.027, which is about three light-years across and has a mass about a thousand times that of our sun, has a temperature of about 100 K. Although there is no evidence that the stars are developing within G+0.693-0.027 now, astronomers believe it may eventually develop into a stellar nursery.
The Doctor. Víctor M. Rivilla, researcher at the Center for Astrobiology of the National Research Council of Spain (CSIC), said: “The chemical content of G+0.693-0.027 is similar to other star-forming regions in our galaxy, and also to solar system objects such as comets. This means that their study could give us important information about the chemical ingredients available in the nebula that give rise to our planetary system.”
Using two telescopes in Spain, the scientists studied the electromagnetic spectra emitted by G+0.693-0.027. They detected the nitriles cyanoallene (CH2CCHCN), propargyl cyanide (HCCCH2CN) and cyanopropyne, which had not yet been found in G+0.693-0.027. However, they were reported in 2019 in the TMC-1 dark cloud in the constellations of Taurus and Auriga, a molecular cloud with very different conditions of G+0.693-0.027.
In addition, the researchers found potential evidence that glycolonitrile (HOCH2CN) and cyanoformaldehyde (HCOCN) were present in sample G+0.693-0027. In the TMC-1 and Sgr B2 molecular clouds in the constellation Sagittarius, cyanoformaldehyde was discovered for the first time, and glycolonitrile was found 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-ethanediol (C2H4O2), confirming that interstellar chemistry can provide the most basic ingredients for the “RNA World.
The final author Dr. Miguel A Requena-Torres, professor at Towson University in Maryland, USA, said: “Thanks to our observations over the last few years, including the current results, we now know that nitriles are among the most abundant chemical families in the universe. We find them in molecular clouds at the center of our galaxy, protostars of different masses, meteorites and comets, and also in the atmosphere of Titan, the largest moon of Saturn.”
The second author Dr. Izaskun Jiménez-Serra, also a researcher at CSIC and INTA, looked ahead: “We detected several simple precursors of ribonucleotides, the building blocks of RNA. But there are still key molecules missing that are difficult to detect. For example, we know that the origin of life on Earth probably also required other molecules, such as lipids, responsible for the formation of the first cells. Therefore, we should also focus on understanding how lipids can be formed from the simplest precursors available in the interstellar medium.”
- Molecular precursors of the RNA world in space: new nitriles in the molecular cloud G+0.693-0.027, Frontiers in Astronomy and Space Sciences (2022). DOI: 10.3389/fspas.2022.876870