Preprint claims detection of four‑carbon sugar erythrulose in Milky Way molecular cloud

A newly posted arXiv preprint says astronomers have detected erythrulose, a four-carbon sugar, in interstellar space for the first time. The claim, posted June 2 as arXiv:2606.03313 and listed as submitted to Nature Astronomy, has not yet been peer reviewed. In the abstract, the authors write: “We report the discovery of erythrulose, a chiral four-carbon ketose, in the ISM.”

If the result holds up, it would expand the inventory of prebiotic molecules — chemicals relevant to the origins of life — known in the interstellar medium, the gas and dust between stars. Sugars are central to biology, and researchers have long been interested in whether some of life’s chemical building blocks could have formed in space before being delivered to young planets by meteorites or asteroids.

The paper, led by Izaskun Jiménez-Serra of the Centro de Astrobiología in Spain and co-authored by 56 other researchers, reports the signal from G+0.693-0.027, a molecular cloud near the center of the Milky Way. The cloud is a frequent target for deep molecular surveys because it is unusually rich in complex chemistry. The reported detection is based on ultrasensitive, broadband spectral surveys taken with the Yebes 40-meter and IRAM 30-meter radio telescopes.

According to the abstract, the team found not just a candidate signal for erythrulose but an unexpectedly strong one relative to similar molecules. “Erythrulose appears to be at least eight times more abundant than analogous three-carbon sugars, which remain undetected in our ultrasensitive observations,” the authors write. They also say quantum-chemical and astrochemical models indicate that erythrulose can form efficiently on interstellar dust grains from simpler two-carbon aldehydes and alcohols.

That matters because dust grains are thought to act as tiny chemical workshops in space, where simple molecules can react and assemble into more complex ones. The authors argue that a confirmed interstellar source of a larger sugar would bolster the case that some biologically relevant compounds may have originated before the solar system formed. In the abstract, they add: “As ketoses readily isomerize into aldoses in aqueous conditions, interstellar erythrulose could have contributed to the sugar inventory available for early metabolic and replication processes.”

G+0.693-0.027 is one of the most molecule-rich clouds known and has been the site of multiple recent detections of complex organic molecules. Searches like this one were also helped by laboratory work: rotational spectroscopy of erythrulose was published in 2021, giving astronomers the frequency fingerprints needed to look for the molecule in radio data.

Still, the new paper is at an early stage. The abstract lays out the headline claim, but it does not include the detailed spectroscopic evidence researchers would typically scrutinize closely, such as which molecular transitions were identified, how cleanly they were separated from other signals, and what alternative explanations were ruled out. Those details may appear in the full paper, but they have not been independently verified here.

That caution is especially important because this should not be framed as an unqualified first sugar in space. Prior literature has already reported glycolaldehyde, often described as the simplest sugar or a sugar-related molecule, in interstellar space. The new preprint is narrower — and potentially significant on its own terms: a claimed first detection of erythrulose, and possibly one of the strongest cases yet for a more complex sugar in the interstellar medium.