The molecule, erythrulose, was identified within G+0.693−0.027, a vast cloud of gas and dust in the Sagittarius B2 region, about 26,000 light-years from Earth. The finding is the first confirmed detection of a true sugar in the interstellar medium and expands the known range of complex organic chemistry occurring between stars.
Erythrulose is a monosaccharide containing four carbon atoms. On Earth, it occurs naturally in foods including raspberries and is also used in some sunless tanning products. Its significance to astronomers, however, lies not in those familiar applications but in its potential role as raw material for chemical reactions associated with metabolism and genetic replication.
The molecule was detected through an ultrasensitive survey conducted with the 40-metre radio telescope at Yebes Observatory and the 30-metre telescope operated by the Institute for Radio Astronomy in the Millimetre Range in Spain. Researchers searched for a distinctive set of rotational signals produced as molecules change energy states.
Each molecular species emits radio waves at a particular collection of frequencies, forming a spectral fingerprint. Multiple signals matching laboratory measurements and theoretical calculations for erythrulose were found in the cloud, allowing the team to distinguish it from the many other compounds present in the crowded region.
The discovery was unexpected because astronomers had been seeking smaller three-carbon sugars. Those simpler molecules remained undetected despite the sensitivity of the observations, while erythrulose appeared to be at least eight times more abundant than comparable three-carbon candidates.
Computer modelling indicates that erythrulose can form efficiently on the frozen surfaces of microscopic dust particles. Simpler molecules containing two carbon atoms may settle on the grains, react under cold interstellar conditions and produce the larger sugar. Radiation, warming or collisions can then release it into the surrounding gas, where radio telescopes can identify it.
Such chemistry challenges the assumption that complex organic compounds require planets, liquid water or living systems. Dense molecular clouds are extremely cold and thin by terrestrial standards, yet they persist for millions of years. That long timescale allows rare reactions to build an increasingly varied chemical inventory.
Sugars are central to biology. Some provide energy, while others form structural components of DNA and RNA. Ribose, a five-carbon sugar, is part of RNA, a molecule widely considered a possible carrier of genetic information during an early stage in the development of life.
Erythrulose is not ribose and its detection does not constitute evidence of life. It can, however, rearrange into related sugars when exposed to water. Researchers believe it could therefore have supplied material for more advanced chemical networks after being incorporated into asteroids, comets or newly forming planets.
The result strengthens the view that part of Earth’s prebiotic inventory may have originated before the solar system formed. The Sun and planets developed from the collapse of a molecular cloud about 4.6 billion years ago. Organic material inherited from that environment could have survived inside small rocky or icy bodies and later reached the young Earth through impacts.
Meteorites and asteroid samples have already provided evidence that sugars can survive beyond planets. Laboratory analysis has identified ribose and other carbohydrates in carbon-rich meteorites, while material returned from asteroid Bennu contains a broad collection of organic compounds associated with biological chemistry.
Those findings had left open the question of whether sugars formed mainly inside asteroids after the solar system appeared or whether their production began earlier in interstellar clouds. The detection of gaseous erythrulose shows that at least some sugar chemistry can precede the birth of a planetary system.
The observation also carries implications beyond Earth. If chemical reactions on icy dust grains routinely produce carbohydrates, young planetary systems across the galaxy may inherit similar ingredients. Their availability would not guarantee life, because biological emergence depends on many environmental and chemical factors, but it could make suitable starting materials more common.
Scientists will now search for other sugars, including three-carbon molecules and compounds more closely linked to RNA. Future surveys with highly sensitive radio observatories could establish whether erythrulose is widespread or concentrated in unusually chemically active clouds near the galactic centre.
Laboratory experiments will also examine how the molecule forms under simulated interstellar conditions and what products it generates after contact with water, minerals and other prebiotic compounds. Those studies may help connect chemistry inside dark molecular clouds with reactions that could occur on the surfaces of young worlds.
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