An international team of astronomers led by Izkintz Jiménez-Serra from the Spanish Astrobiology Center (CAB) has announced an unprecedented discovery: a true sugar, erythrulose, a four-carbon ketose known to Earthlings as a component of raspberries and tanning cosmetics, has been detected in the interstellar medium for the first time. The discovery is published in the journal "Nature Astronomy" and available as a preprint on arXiv.org under number 2606.03313.
The astronomers pointed two radio telescopes – the 40-meter telescope of the Yebes Observatory (Spain) and the 30-meter IRAM telescope (international observatory) – at the molecular cloud G+0.693-0.027, located in the Central Molecular Zone of our Galaxy at a distance of about 26.7 thousand light-years from the Sun. Observations were conducted from March 2021 to April 2024 and covered over 91 GHz in the 7 mm, 3 mm, and 2 mm bands. The team detected 12 spectral lines that precisely match the laboratory spectrum of erythrulose, measured at the University of the Basque Country. The reliability of the discovery is confirmed by a low probability of random coincidence (only 0.2%).
It might seem like a curious fact, but is it important? It is important, and here's why. Sugars are fundamental biomolecules essential for life. They serve as an energy source, are components of DNA and RNA, and participate in metabolic processes. The question of how simple sugars ended up on early Earth remains one of the central issues in the study of the origin of life.
Previously, ribose, glucose, and other monosaccharides had been found in meteorites and asteroids (including the soil of asteroid Bennu), suggesting a possible exogenous origin. However, no true sugar had ever been detected in the interstellar medium until now. The only known related compound was glycolaldehyde – the simplest diose, classified as a hydroxyaldehyde, not a true saccharide.
The classical model of complex molecule formation in space assumes a step-by-step build-up: first, a molecule with one carbon atom forms, then one with two, then one with three – and so on. But with erythrulose, things turned out differently. Researchers, including Jiménez-Serra, proposed an unexpected explanation: erythrulose is not formed gradually but by the combination of two two-carbon fragments – glycolaldehyde and ethylene glycol molecules – directly on the icy surface of cosmic dust grains. These molecules collide, stick together under the influence of cosmic radiation, and a four-carbon ketose is born.
Quantum chemical calculations and computer astrochemistry modeling confirmed that this mechanism works at temperatures around 20-30 K (which is about minus 250 degrees Celsius), typical for icy dust grains in the Galactic Center – the region where the find was made.
Erythrulose was found to be at least 8-17 times more abundant than the three-carbon sugars glyceraldehyde and dihydroxyacetone, which were not detected at all in the cloud G+0.693-0.027. It possesses several unique properties:
- The first sugar discovered in the interstellar medium
- The second chiral molecule in interstellar space (with an asymmetric structure, like a left and right hand)
- The largest acyclic (non-cyclic) molecule of 14 atoms identified in the interstellar medium.
The discovery overturns our understanding of how life may have originated. Ketoses like erythrulose can easily be converted in aqueous environments into aldoses – specifically, into threose, which is a simple pentose (a five-carbon sugar). Threose, in turn, is considered a possible precursor to RNA – a molecule that many scientists believe was the first genetic material of life on Earth.
Researchers hypothesize the following scenario: sugars formed in our protoplanetary nebula (the gas and dust cloud from which the Sun and planets formed), then became part of small bodies – comets and asteroids, and were delivered to the young Earth through meteorite bombardment. According to calculations, during the Late Heavy Bombardment (approximately 4.1–3.8 billion years ago), between 0.5 and 50 million tons of this sugar could have fallen onto our planet's surface. These enormous quantities of organic matter could have contributed to the formation of prebiotic soups – chemical baths in which the first molecules of life originated.
The discovery of erythrulose opens a new frontier in astrochemistry and astrobiology. Scientists will now purposefully search for other sugars in interstellar clouds and protoplanetary disks – primarily ribose and deoxyribose, which form the basis of modern DNA and RNA. This research could reveal how universal the processes of key biomolecule formation are in space.
The discovery also confirms that complex prebiotic molecules not only form but also survive in the extreme conditions of the interstellar medium – in cold, rarefied gas, under bombardment by cosmic rays. This means such molecules could be widespread throughout our Galaxy and beyond. And this, in turn, greatly expands our understanding of how many worlds in the universe could harbor life similar to Earth's.
