Cometary Glycolaldehyde as a Source of pre-RNA Molecules

Abstract

Over 200 molecules have been detected in multiple extraterrestrial environments, including glycolaldehyde (C 2 (H 2 O) 2 , GLA), a two-carbon sugar precursor that has been detected in regions of the interstellar medium. Its recent in situ detection on the nucleus of comet 67P/Churyumov-Gerasimenko and through remote observations in the comae of others provides tantalizing evidence that it is common on most (if not all) comets. Impact experiments conducted at the Experimental Impact Laboratory at NASA's Johnson Space Center have shown that samples of GLA and GLA mixed with montmorillonite clays can survive impact delivery in the pressure range of 4.5 to 25 GPa. Extrapolated to amounts of GLA observed on individual comets and assuming a monotonic impact rate in the first billion years of Solar System history, these experimental results show that up to 10 23 kg of cometary GLA could have survived impact delivery, with substantial amounts of threose, erythrose, glycolic acid, and ethylene glycol also produced or delivered. Importantly, independent of the profile of the impact flux in the early Solar System, comet delivery of GLA would have provided (and may continue to provide) a reservoir of starting material for the formose reaction (to form ribose) and the Strecker reaction (to form amino acids). Thus, comets may have been important delivery vehicles for starting molecules necessary for life as we know it.

Glycine amino acid transformation under impacts by small solar system bodies, simulated via high-pressure torsion method

“…Although current HPT experiments did not provide any positive support for the formation of protein from glycine by astronomical impact events, the formation of protein from other amino acids by HPT processing needs to be investigated in the future. The stability of significant amounts of glycine after the HPT process indicates that comet impacts could basically deliver significant amounts of biomolecules into the early Earth, as suggested in some other studies by high-pressure shock experiments as well 25,26 . As discussed in the previous paragraph, the conversion of glycine to ethanol implies the release of nitrogen-containing molecules and some reactive gases into the system, which are inevitably available to react with other molecules to produce other organic compounds on the Earth.…”

“…In this study, we apply the HPT method for the first time to glycine amino acid to have an insight into the survival of amino acids or the formation of protein by astronomical impact events. The findings of this study are of significance for astrobiology because the degree of survival of organic materials during impacts by small solar system bodies is an important issue in understanding the delivery of necessary molecules for life onto the Earth by comets and other small solar system bodies 25,26 . Moreover, the formation mechanism of proteins from amino acids in the early Earth conditions is still a key issue in understanding the origin of life 1,8 .…”

Molecular Precursors of the RNA-World in Space: New Nitriles in the G+0.693−0.027 Molecular Cloud

“…Marchi et al, 2014). Laboratory impact experiments have shown that a significant fraction of the molecules contained in comets and meteorites could have been delivered intact to the early Earth (Pierazzo and Chyba 1999;Bertrand et al, 2009;McCaffrey et al, 2014;Todd and Öberg 2020;Zellner et al, 2020). Once on the planetary surface, under the appropriate physical/chemical conditions, these molecules could have allowed the development of the prebiotic processes that led to the dawn of life on Earth.…”

Molecular precursors of the RNA-world in space: new nitriles in the G+0.693-0.027 molecular cloud

“…Marchi et al 2014). Laboratory impact experiments have shown that a significant fraction of the molecules contained in comets and meteorites could have been delivered intact to the early Earth (Pierazzo and Chyba 1999;Bertrand et al 2009;McCaffrey et al 2014;Zellner et al 2020;Todd and Öberg 2020). Once on the planetary surface, under the appropriate physical/chemical conditions, these molecules could have allowed the development of the prebiotic processes that led to the dawn of life on Earth.…”