New research shows molecular clouds are laden with important precursors to life on Earth. This image shows the “pigtail” molecular cloud. Photo credit: Keio University, NAOJ
Important progenitors for life on Earth are abundant in interstellar molecular clouds and may have arrived on Earth in comets and meteors.
Nitriles, a class of organic molecules containing a cyano group (a carbon[{” attribute=””>atom bound with a triple unsaturated bond to a nitrogen atom) are typically toxic. But paradoxically, they are also a key precursor for molecules essential for life on Earth, such as ribonucleotides, composed of the nucleobases or ‘letters’ A, U, C, and G joined to a ribose and phosphate group, which together make up
“Here we show that the chemistry that takes place in the interstellar medium is able to efficiently form multiple nitriles, which are key molecular precursors of the ‘RNA World’ scenario,” said 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 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
According to this scenario, life on Earth was originally based on RNA only, and protein enzymes and
Amino acids are a set of organic compounds used to build proteins. There are about 500 naturally occurring known amino acids, though only 20 appear in the genetic code. Proteins consist of one or more chains of amino acids called polypeptides. The sequence of the amino acid chain causes the polypeptide to fold into a shape that is biologically active. The amino acid sequences of proteins are encoded in the genes. Nine proteinogenic amino acids are called “essential” for humans because they cannot be produced from other compounds by the human body and so must be taken in as food.
” data-gt-translate-attributes=”[{” attribute=””>amino acids have been found inside contemporary meteors and comets.
Where in space could these molecules have come from? Prime candidates are molecular clouds, which are dense and 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 around 100 K and is approximately three light-years across, with a mass approximately one thousand times that of our Sun. Although scientists suspect that it might evolve to become a stellar nursery in the future, there’s no evidence that stars are currently forming inside G+0.693-0.027.
“The chemical content of G+0.693-0.027 is similar to those of other star-forming regions in our galaxy, and also to that of solar system objects like comets. This means that its study can give us important insights about the chemical ingredients that were available in the nebula that give rise to our planetary system,” explained Rivilla.
Electromagnetic spectra studied
Rivilla and colleagues used two telescopes in Spain to study the electromagnetic spectra emitted by G+0.693-0.027: the 30-meter-wide IRAM telescope Granada, and the 40-meter-wide Yebes telescope in Guadalajara. They detected the nitriles cyanoallene (CH2CCHCN), propargyl cyanide (HCCCH2CN), and cyanopropyne, which hadn’t yet been found in G+0.693-0.027, although they had been reported in 2019 in the TMC-1 dark cloud in the constellations Taurus and Auriga, a molecular cloud with very different conditions than G+0.693-0.027.
Rivilla et al. also found possible evidence for the occurrence in G+0.693-0.027 of cyanoformaldehyde (HCOCN) and glycolonitrile (HOCH2CN). Cyanoformaldehyde was detected for the first time in the molecular clouds TMC-1 and Sgr B2 in the constellation Sagittarius, and glycolonitrile in the Sun-like protostar IRAS16293-2422 B in the constellation Ophiuchus.
Other recent studies have also reported other RNA precursors inside G+0.693-0.027 such as glycolaldehyde (HCOCH2OH), urea (NH2CONH2), hydroxylamine (NH2OH), and 1,2-ethenediol (C2H4O2), confirming that the interstellar chemistry is able to provide the most basic ingredients for the ‘RNA World’.
Nitriles among most abundant chemical families in space
Final author Dr. Miguel A Requena-Torres, a lecturer at Towson University in Maryland, US, concluded: “Thanks to our observations over the past few years, including the present results, we now know that nitriles are 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, the largest moon of
