First genuine sugar found in interstellar space, 27,000 light-years from Earth

First genuine sugar found in interstellar space

Astronomers have detected the sugar molecule erythrulose in a cold gas cloud named G+0.693-0.027, located roughly 27,000 light-years from Earth near the centre of the Milky Way. The discovery, published on 14 July in Nature Astronomy, is the first direct identification of a genuine sugar in the interstellar medium, the thin gas and dust spread between stars. Erythrulose is a monosaccharide composed of four carbon, eight hydrogen and four oxygen atoms. On Earth it gives raspberries their sweetness, belongs to the same chemical family as ribose and glucose, and is used in self-tanning products because it reacts with skin proteins to produce a temporary brown colour.

How the detection was made

The signal was captured by two radio telescopes in Spain: the 40-metre dish at Yebes and the 30-metre IRAM antenna at Pico Veleta. By matching 12 sets of radio emissions with laboratory spectra measured at the University of the Basque Country, an international team led by Izaskun Jiménez-Serra of the Centro de Astrobiología (CAB) confirmed the identity of erythrulose. The cloud G+0.693 sits only about 450 light-years from the galactic centre, a region through which NASA's twin Voyager probes have passed on their journey outward.

Building blocks for life

Erythrulose itself is not essential for life as we know it, but it can easily react to form threose. Threose is the sugar backbone of threose nucleic acid (TNA), a simpler genetic polymer that some researchers believe may have preceded RNA in early biochemistry. The newly found sugar is chiral, existing in two mirror-image forms, a property that can influence how biological molecules interact. Earlier discoveries had already shown that complex organic molecules can form in space: about 25 years ago a cousin of table sugar was spotted near the galactic centre; ribose, a key component of RNA, was extracted from two meteorites in 2019; glucose turned up in black grains returned from asteroid Bennu by NASA's OSIRIS-REx mission; and in 2023 the amino acid tryptophan was detected in a star-forming cloud.

An unexpected abundance

According to standard astrochemical models, larger molecules should be rarer than smaller ones. Yet the team found that erythrulose was at least eight times and possibly up to 17 times more abundant than comparable sugars with only three carbon atoms, which were not detected at all in the same cloud or in previously studied regions. Laboratory experiments with chemists from the University of Extremadura and Radboud University in the Netherlands suggest an explanation: erythrulose can form on the icy surfaces of interstellar dust grains from simple two-carbon alcohols and aldehydes, bypassing the need for a gradual step-by-step addition of carbon atoms. At 14 atoms, erythrulose is the largest non-cyclic molecule ever identified in the interstellar medium and the first there to contain four oxygen atoms.

What experts say

Astrophysicist Erika Hamden of the University of Arizona, who was not involved in the study, called the finding a pristine example of organic matter drifting in the galaxy.

It's a pristine example of the stuff that simply floats around the galaxy.

Study co-author Carlos Briones said the result opens a path toward spotting even larger sugars.

The detection of erythrulose in a molecular cloud is an exciting discovery because it opens the possibility of identifying larger sugars (such as ribose, which is a component of RNA) and other molecules relevant to the origin of life in the interstellar medium.

Leiden University astronomer Michiel Hogerheijde noted that astronomers broadly agree that all of life's ingredients are present in many places in the universe, but the timing and mechanism of their assembly remain open questions.

It is plausible that impacts on the young Earth of planetoids or meteorites, with their supply of sugars, could have given the origin of life a nudge in the right direction.

A timeline of interstellar sugars

The journey from simple molecules to the building blocks of genetics has been traced step by step.