The center of the Milky Way in infrared, a mosaic built from Hubble and Spitzer observations, showing dense glowing gas, dust, and millions of stars around the galactic core. Credit: NASA, ESA and Q.D. Wang (University of Massachusetts, Amherst).
The center of the Milky Way in infrared, a mosaic built from Hubble and Spitzer observations. The bright, dense region around the galactic core is full of the giant molecular clouds where interstellar chemistry happens. The sugar erythrulose was detected in the cloud G+0.693−0.027, a few hundred light-years from the galactic center. Credit: NASA, ESA and Q.D. Wang (University of Massachusetts, Amherst).

In July 2026, astronomers announced that they had found a sugar in interstellar space for the first time. Not a molecule that vaguely resembles a sugar, and not a sugar on a comet or an asteroid. A true sugar, floating in gas and dust between the stars, in a cloud a few hundred light-years from the center of the Milky Way.

The molecule is erythrulose, a four-carbon monosaccharide. It is the same sugar found in raspberries, and it is also used in self-tanning products. It is the first true sugar ever detected beyond our solar system, and its discovery, published in Nature Astronomy by a team led by Izaskun Jiménez-Serra of Spain's Center for Astrobiology (CAB), feeds directly into one of biology's oldest questions: where did the chemistry of life come from?

More than 340 molecules have now been identified in the interstellar medium, the thin gas and dust between the stars. Nearly 30 of them are tied to the chemistry of life: precursors of amino acids, of the building blocks of RNA, of the molecules that make cell membranes. But none of them was a sugar. That gap lasted for decades, and it was strange, because sugars are everywhere in biology.

What counts as a sugar, and why this was the first

Sugars are simple carbohydrates: molecules built from carbon, hydrogen, and oxygen, with a backbone of carbon atoms and a characteristic arrangement of chemical groups. Chemists group them by the number of carbons in the chain. A two-carbon sugar is a diose. Three carbons, a triose. Four, a tetrose. Five, a pentose, which is where ribose lives, the sugar that forms the backbone of RNA.

By a chemist's definition, the smallest true sugars have at least three carbons. That distinction matters, because in 2000 astronomers detected glycolaldehyde, a two-carbon molecule, toward the galactic center and some news coverage called it a sugar. Glycolaldehyde is a diose, a two-carbon compound, and while it is a crucial precursor, it is not formally a sugar.

"We have previously reported the detection of precursors of ribonucleotides, precursors of protolipids, and precursors of amino acids, but this is the first sugar," Jiménez-Serra said.

Erythrulose is a tetrose: a four-carbon sugar. It is a ketose, meaning its sugar chemistry is built around a ketone group, a specific arrangement of a carbon double-bonded to an oxygen. And it is chiral, meaning it comes in two mirror-image forms, like a pair of gloves.

How you find a sugar in a cloud 27,000 light-years away

The cloud in question is cataloged as G+0.693−0.027, a giant molecular cloud near the galactic center, the region Jiménez-Serra calls the richest chemical repository in the Milky Way. Large columns of gas and dust there concentrate molecules that formed on icy dust grains, then released into the gas, which makes them comparatively easy to detect.

The detection method is called rotational spectroscopy. In the cold cloud, molecules rotate, and each molecule rotates at specific frequencies determined by its exact shape and mass. As they spin, they emit radio waves at those frequencies, like a fingerprint in the radio spectrum. Point a sensitive radio telescope at the cloud, and every molecule present contributes its own pattern of lines.

The team used two dish-shaped radio telescopes in Spain: the 40-meter Yebes telescope and the 30-meter IRAM telescope on Pico Veleta in the Sierra Nevada. They collected ultrasensitive broadband spectra of the cloud, then compared the observed lines against laboratory measurements of erythrulose's rotational spectrum.

The white dish of the IRAM 30-meter radio telescope on Pico Veleta in Spain's Sierra Nevada, seen against a twilight sky over snowy mountains.
The IRAM 30-meter telescope on Pico Veleta, Spain, one of the two radio telescopes used to detect erythrulose in the molecular cloud G+0.693−0.027. The other was Spain's 40-meter Yebes telescope. Photo: IRAM (CC BY-SA 4.0).

Measuring the sugar's spectrum in the lab was itself an achievement. Sugars are difficult to vaporize without decomposing, so the team mixed erythrulose with talc, which helped release intact gas-phase molecules for the spectroscopic measurements. Then they identified and modeled more than 180 molecular species in the observational dataset, to determine which erythrulose signals were free of interfering emission from other molecules.

"I was looking at the data without any hope because we hadn't detected the three-carbon sugars," Jiménez-Serra said. "Then I started seeing that all the transitions were matching signals present in the observations."

The surprise: it skipped a step

The detection carries a puzzle that has astrochemists excited. In interstellar space, larger molecules generally form less often than smaller ones: building a bigger molecule takes more steps, so it should be rarer. By that logic, three-carbon sugars should be easier to find than four-carbon ones.

The team looked. The three-carbon sugars were not there, or at least not above the detection limit. Meanwhile, the four-carbon erythrulose appears to be at least eight times more abundant than its analogous three-carbon sugars would be.

"We've never managed to detect a sugar outside of our solar system," said Brett McGuire, a chemist at MIT who was not involved in the study. "And now we skipped all the three-carbon sugars and went straight to four carbons. That's astonishing."

The finding overturns the usual assumption that interstellar molecules grow one carbon at a time, by sequential addition of single atoms. Instead, the team's quantum chemical calculations and astrochemical simulations suggest erythrulose forms when two abundant two-carbon molecules, glycolaldehyde and ethylene glycol, react on the surfaces of icy dust grains. Two mid-sized pieces combine into one larger sugar, a pathway that sidesteps the missing three-carbon rungs.

"This chemistry is weird and unexpected, meaning it goes against our chemical intuition," McGuire said. "That's exciting because it opens an entirely new avenue to explore, and it might give us clues for other larger, more complex sugars that we should be looking for."

Icy dust grains as a sugar factory

Conceptual illustration of a small icy dust grain in space: a dark rocky core coated in pale blue ice, with small simple molecules stuck to the icy surface and a larger sugar molecule forming where they meet, while similar molecules drift away into dark space dotted with faint stars.
How a sugar might form before any star exists: small molecules stick to the icy surface of a dust grain in a cold cloud, react, and the resulting sugar is released into the gas. The process shown here is a conceptual illustration, not a literal chemical diagram. Illustration: Impossible Universe Editorial Team (generated).

Molecular clouds are the coldest, emptiest places where chemistry demonstrably happens. Temperatures hover near absolute zero, and pressures are far lower than any laboratory vacuum on Earth. Individual chemical reactions occur only rarely, but the clouds persist for millions of years, and that is enough time for simple molecules to accumulate on dust grains, react on the icy surfaces, and build increasingly complex organics before the cloud collapses to form stars and planetary systems.

The new result places sugars on that list. "What we know for certain is that these molecules formed during the initial conditions of the process of planetary formation, even before a star or a planet forms," Jiménez-Serra said.

That is the piece that matters for the origin of life. Ribose, the sugar at the backbone of RNA, is also a monosaccharide, and RNA is widely thought to have played a central role in the earliest biology. If sugars can form in interstellar space, before planets exist, then the raw material for RNA's backbone was available in the clouds from which solar systems are built.

Two delivery routes, one open question

Sugars have reached planets by at least two routes, and the new detection clarifies the first of them. Ribose and other sugars have been found inside meteorites, including in analyses led by Yoshihiro Furukawa's group (PNAS 2019; Nature Geoscience 2026). Those sugars formed or were preserved inside asteroid parent bodies, then rode to Earth inside rocks. The interstellar detection opens the other route: sugars synthesized in cold clouds, incorporated into comets and asteroids as the cloud collapses, and delivered to young planets by impacts.

Erythrulose itself is not essential for life as we know it, but it converts readily into forms that are. In water, ketoses like erythrulose isomerize into aldoses, the other major family of sugars. "It's not essential for life, but can easily convert to a form that's thought to be crucial to kick-starting life on Earth," said Erika Hamden of the University of Arizona, who was not involved in the work.

Finding erythrulose in one cloud suggests the chemistry is not rare. "Finding them in one spot means they're likely also hiding in distant corners of the galaxy along with other important bits," Jiménez-Serra said.

What the discovery does and does not say

It is worth being precise about the claims. The detection is a single cloud, identified by matching multiple spectral lines against laboratory measurements, and the team modeled more than 180 other molecular species to rule out interference. That is a solid identification, but it is one cloud.

The "first true sugar" framing depends on definition. Glycolaldehyde, detected in 2000, is sometimes loosely called a sugar in news coverage, but it is a two-carbon diose, not formally a sugar. Erythrulose is the first true monosaccharide found in interstellar space, and the paper is careful about that distinction.

And the link to life's origins is a hypothesis, not a measured pathway. Astronomers have shown the sugar exists out there and that it forms before stars and planets. Whether interstellar sugars actually seeded early Earth's chemistry is a separate question, one that connects to the ribose-in-meteorites results and to the wider question of how life's building blocks came together. Each new molecule detected in these clouds adds a piece to that puzzle, and the sugar-shaped piece was missing for a very long time.

Sources

Hero image: composite infrared mosaic of the galactic center from NASA, ESA and Q.D. Wang (University of Massachusetts, Amherst), released by ESA/Hubble, used under the ESA/Hubble image use policy with credit. Inline telescope photo: IRAM (CC BY-SA 4.0, via Wikimedia Commons). Sugar formation diagram: conceptual illustration generated by the Impossible Universe Editorial Team based on the formation pathway described in the cited sources.

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