First sugar detected in the interstellar medium

Radio telescopes have detected a four-carbon sugar in the interstellar medium, which is the largest non-cyclic molecule and the first sugar to be identified. The researchers say this shows that chiral, prebiotic molecules can form and survive under the extreme conditions of space. Such molecules could have been brought to Earth via asteroids, helping to kickstart life on Earth, the researchers note.

More than 340 molecules have been detected in the interstellar medium so far, including urea, hydroxylamine and ethanolamine. Sugars – such as ribose and glucose – have only been detected on meteorites and asteroids.

Spanish radio telescopes have now allowed an international team to detect the sugar erythrulose (C₄H₈O₄) in the Galactic Centre region – a molecule-rich area of the Milky Way around 26,000 light years away. Ultrasensitive spectroscopes allowed the team to detect the sugar’s molecular rotations, which was previously difficult to do with conventional techniques.

Quantum chemical and astrochemical models suggest that erythrulose could form by combining glycolaldehyde (C₂H₄O₂) and ethylene glycol (C₂H₆O₂) on the surface of interstellar dust grains. Erythrulose readily isomerises in aqueous conditions into the aldehyde-containing isomers threose and erythrose. Such molecules are involved in the formation of ribose, the sugar at the heart of nucleic acids.

Detecting erythrulose in the interstellar medium means these sugars could have been a source of extraterrestrial prebiotic molecules, the researchers note, and subsequently brought to Earth on asteroids. The team estimates that around 0.5 to 5 million tonnes of erythrulose could have been delivered to early Earth during the Late Heavy Bombardment around 4 billion years ago.