A team led by Spain’s Center for Astrobiology has detected erythrulose, a four-carbon sugar, inside a gas cloud near the center of the Milky Way.
The detection marks the first time a sugar molecule has ever been recorded in interstellar space, according to a study published July 13 in Nature Astronomy.
Erythrulose is the same compound responsible for the color of raspberries — and the active ingredient in most self-tanning lotions.
The molecule was detected in G+0.693−0.027, a molecular cloud of gas and dust located roughly 27,000 light-years from the galactic center. It is the same region where the team had previously identified precursors to nucleotides, lipids, and amino acids.
How the Detection Was Made
The researchers, led by astrochemist Izaskun Jimenez-Serra of the Center for Astrobiology (CSIC-INTA), trained two Spanish radio telescopes on the cloud: the 131-foot dish at Yebes, north of Madrid, and the 98-foot telescope operated by the Institute for Millimeter Radio Astronomy in the Sierra Nevada.
Both instruments captured twelve spectral lines that matched the laboratory spectrum of erythrulose, previously measured at the University of the Basque Country.
The discovery also revealed something unexpected.
Erythrulose turned out to be at least eight times more abundant than the three-carbon sugars the team had been searching for in the same region — none of which appeared in the observations at all.
A Result That Doesn’t Fit the Model
That absence matters. It contradicts the model astrochemists have long used to explain how molecules grow in space — one carbon atom at a time.
If that model were correct, three-carbon sugars should have appeared before the four-carbon variety, and in greater quantities.
The team’s working explanation is different. Erythrulose may have formed directly when two two-carbon molecules combined — glycolaldehyde and ethylene glycol — both of which have already been detected in the interstellar medium.
Brett McGuire, an astrochemist at MIT who was not involved in the study, described the result as a departure from what known chemistry would predict.
Prior to this discovery, nearly 30 molecules linked to prebiotic chemistry had already been identified in space, including glycolaldehyde, first detected in 2000.
That molecule, however, is not considered a true sugar. According to McGuire, a carbohydrate must contain at least three carbon atoms to qualify.
Erythrulose is, for now, the most complex sugar ever found outside the Solar System.
From Molecular Cloud to Primordial Earth
Molecular clouds like G+0.693−0.027 are the raw material from which stars, planets, asteroids, and comets eventually form.
That raises the question of what happened to the erythrulose after it formed.
According to the team’s calculations, somewhere between 606,000 and 60.6 million tons of this sugar may have reached Earth roughly 4 billion years ago, carried by asteroids and comets during the intense bombardment the young planet endured in its earliest stages.
That figure echoes earlier findings from asteroid samples. In March, a separate study reported that asteroid Ryugu contains all five nitrogen bases required to build DNA and RNA.
Similar findings had previously been reported for samples from asteroid Bennu.
Sugars, along with those bases and phosphate groups, make up the three essential components of nucleic acids.
Caution and Next Steps
Yoshihiro Furukawa, an astrochemist at Tohoku University who also had no role in the study, said the finding points to a way sugar could be distributed through space other than by asteroid delivery, and noted that the scientific community had long been waiting for a direct detection of this kind.
The Spanish team is quick to point out that the discovery does not prove that the erythrulose found in this particular cloud is the same sugar that reached the early Earth.
What it does prove is that the conditions necessary to form complex sugars exist in interstellar space, entirely independent of any planet.
How common that process is elsewhere in the galaxy remains an open question for now.
