Scientists have detected a key four-carbon sugar in interstellar space that may have contributed to the rise of life on Earth.
Researchers from Centro de Astrobiología (CAB), the Spanish Astrobiology Centre, in Torrejón de Ardoz, Madrid, have identified sugar molecules in clouds of interstellar gas, using the Yebes 40 m (Guadalajara, Spain) and IRAM 30 m (Granada, Spain) radio telescopes (Nature Astronomy, 2026, DOI:10.1038/s41550-026-02905-7).
Although ribose, glucose and other monosaccharides have previously been identified in asteroids and meteorites, this is the first time a monosaccharide – erythrulose - has been discovered in the space between star systems, so-called interstellar medium (ISM). It was detected toward the molecular cloud G+0.693−0.027, located near the centre of the Milky Way.
The researchers describe the ISM as ‘impressive chemical factory’ as more than 340 molecules have been detected there, including large aromatic species. Several of these molecules, such as urea, hydroxylamine and ethanolamine, are directly connected to origin-of-life chemistry because they are considered precursors of ribonucleosides and lipids.
While sugars are also central to prebiotic chemistry, they usually have to be introduced in prebiotic reaction schemes because their formation under plausible early-Earth conditions is said to be inefficient.
The researchers report quantum chemical and astrochemical models indicate that erythrulose forms efficiently on interstellar dust grains from simpler two-carbon aldehydes and alcohols glycolaldehyde and ethylene glycol. Erythrulose, with 14 atoms in its structure, represents the largest non-cyclic molecular species identified so far in the ISM, and the first detected molecule containing four oxygen atoms. As ketoses readily isomerise into aldoses in aqueous conditions, interstellar erythrulose could have contributed to early metabolic and replication processes.
Prebiotic chemistry experiments have shown that ribonucleotides—the building blocks of RNA—can be synthesised from mixtures containing sugars such as erythrulose. Ketoses such as erythrulose can readily isomerise into their aldose counterparts threose and erythrose, in aqueous environments, a transformation that is central to the formation of ribose and then nucleic acids.
The team estimates up to 50m t of erythrulose, which on Earth can be found in raspberries and fake tan products, could have reached the surface of the plant on the surface of cosmic dust during the period of the Late Heavy Bombardment (LHB), between 4.1 and 3.9bn years ago, by space debris, such as meteors and asteroids.
Although the extent and intensity of the LHB have been questioned, the researchers say Monte-Carlo simulations of Earth’s impact history show that biopoiesis—the process describing the development of living matter from non-living organic matter—could occur within a much broader timeline between 4.45 and 3.9bn years ago with at least a 16% chance.
According to the researchers, the presence of erythrulose on the surface of a primitive Earth and its rapid isomerisation into threose support its involvement in the formation of threose nucleic acid (TNA), a structurally simpler RNA analogue and the simplest of all potential sugar-containing nucleic acids. Threose nucleic acid has been synthesised and has been proposed as one of the polymers that could have been involved in a pre-RNA world.
As such, the discovery of interstellar erythrulose suggests that the ISM could be a viable source of sugar feedstock for the prebiotic synthesis of the first nucleic acids, not only on primitive Earth - but also elsewhere in the Universe.
"The detection of erythrulose is very exciting because it opens up the possibility of discovering in space other sugars such as ribose, which is part of RNA, and other important molecules for the origin of life," said Carlos Briones, co-author of the study.
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