Key Sugar Precursor Found in Deep Space

The Sugar Molecule That Shouldn’t Exist in Space

The molecular cloud G+0.693-0.027 sits in the center of our galaxy, a dense, cold knot of gas and dust. Astronomers have been picking through its chemical inventory for years, and they have found the usual suspects: methanol, formaldehyde, glycolaldehyde, the simple building blocks of life. But in 2022, a team led by Victor M. Rivilla at the Scuola Normale Superiore di Pisa announced something strange. They had detected (Z)-1,2-ethenediol, a molecule that is basically the enol form of glycolaldehyde. That is a technical way of saying it is a sugar precursor that, by all chemical logic, should have broken apart long before anyone could find it in space.

They found it anyway. And its presence changes how we think about where the ingredients for RNA, and possibly life, actually come from.

The molecule is a simple one: two carbon atoms, each bonded to an oxygen and a hydrogen, with a double bond between the carbons. Chemically, it is an enol, a class of molecules that are notoriously unstable. In a glass flask on Earth, (Z)-1,2-ethenediol would isomerize into glycolaldehyde in minutes. But in the vacuum of space, at temperatures just a few degrees above absolute zero, it hangs around. Rivilla and his colleagues measured its column density at (1.8 ± 0.1) × 10^13 per square centimeter (Rivilla et al., 2022). That translates into an abundance of about 1.3 molecules for every 10 billion hydrogen molecules. That is not a lot, but it is enough to matter.

The detection was not an accident. The team had been systematically searching for enols in the interstellar medium, because enols are the missing link in a long-standing puzzle: how do simple carbon molecules assemble into the sugars that make up RNA? Glycolaldehyde, a two-carbon sugar, had been found in space before. But the step between glycolaldehyde and the three-carbon sugars that form the backbone of RNA had remained a mystery. (Z)-1,2-ethenediol is the molecule that sits in that gap. It is the key intermediate.

How You Catch a Molecule That Doesn’t Want to Exist

The Radio Telescope as Chemical Detective

Rivilla and his team used the IRAM 30-meter radio telescope in Spain. They pointed it at the G+0.693-0.027 molecular cloud, which is about 26,000 light years away, near the center of the Milky Way. The cloud is a hotbed of star formation and chemical activity. It is also a mess: dense, turbulent, and filled with dozens of different molecules, each emitting its own signature in the radio spectrum.

The trick to detecting a specific molecule is to know exactly what frequencies it emits. Molecules rotate and vibrate at precise energies, and when they change states, they release photons at specific radio frequencies. For (Z)-1,2-ethenediol, Rivilla and his team calculated what these frequencies should be based on quantum mechanics. Then they went looking for them.

They found three distinct rotational transitions of the molecule, all at frequencies between 80 and 90 gigahertz. Each transition matched the predicted pattern exactly. That is the gold standard for molecular detection in astronomy: multiple lines, all consistent with one molecule, none explained by anything else (Rivilla et al., 2022).

Why This Cloud Matters

G+0.693-0.027 is not just any cloud. It is what astronomers call a molecular cloud in the Galactic Center, which means it is exposed to high levels of cosmic rays and ultraviolet radiation. That might sound hostile to chemistry, but it is actually the opposite. The radiation drives reactions that would not happen in quieter parts of the galaxy. It breaks apart simple molecules into radicals, which then recombine into more complex ones.

This cloud has already yielded detections of glycolaldehyde, ethylene glycol, and even amino acids. It is essentially a chemical factory. Finding (Z)-1,2-ethenediol there suggests that sugar formation is not just possible in space; it is active, ongoing, and probably common.

The Chemistry of the First Sugar

From Two Carbons to Three

RNA is built from ribose, a five-carbon sugar. But the first step toward ribose is making a three-carbon sugar called glyceraldehyde. For years, the only known way to get glyceraldehyde in space was through a reaction called the formose reaction, which starts with formaldehyde and proceeds through a series of steps. The formose reaction works on Earth, but it requires liquid water and a base catalyst. Neither of those exists in interstellar space.

Rivilla and his team propose a different route. They suggest that (Z)-1,2-ethenediol can combine with a radical called hydroxymethylene (CHOH) to form glyceraldehyde directly (Rivilla et al., 2022). This reaction does not need water or a base. It can happen on the surface of interstellar dust grains, where molecules are frozen into icy mantles and react when hit by cosmic rays or ultraviolet photons.

This is a big deal. It means that the basic building blocks of RNA can form in the coldest, emptiest parts of the galaxy, without any of the conditions we normally associate with life. The ingredients are just floating there, waiting to be assembled.

The Abundance Ratio Tells a Story

Rivilla and his team also measured the ratio of glycolaldehyde to (Z)-1,2-ethenediol in the cloud. It is about 5.2 to 1 (Rivilla et al., 2022). That ratio is a clue. If the two molecules were in thermodynamic equilibrium, the enol form would be almost nonexistent. It is too unstable. The fact that it is present at all, and in a ratio that is not wildly skewed, suggests that the enol is being formed continuously, probably from the same precursors that make glycolaldehyde.

The authors identify several possible formation routes. One involves the reaction of the formyl radical (HCO) with formaldehyde (H2CO). Another uses the hydroxymethylene radical (CHOH) with itself. A third involves the vinyl alcohol molecule (CH2CHOH). All of these are common in the interstellar medium. The point is that (Z)-1,2-ethenediol is not a freak accident. It is a natural byproduct of the normal chemistry of space.

What This Means for the Origin of Life

The RNA World Gets a New Starting Point

The RNA world hypothesis proposes that life began with self-replicating RNA molecules, long before DNA or proteins existed. But that hypothesis has always had a weak spot: where did the RNA come from? Ribose, the sugar in RNA, is hard to make without enzymes. And even if you make it, it is fragile. It breaks down quickly in water.

Finding (Z)-1,2-ethenediol in space does not solve the whole problem, but it does move the goalposts. It shows that the first steps toward sugar formation can happen in environments that are not warm, wet, or protected. The molecules can form in space, then be delivered to planets by comets or meteorites. That makes the origin of RNA less of a fluke and more of a predictable outcome of cosmic chemistry.

A Universal Chemical Grammar

There is a deeper implication here. The chemistry that produces (Z)-1,2-ethenediol is not specific to our galaxy. The same reactions should happen anywhere that carbon, oxygen, and hydrogen exist in the right proportions. And those elements are among the most abundant in the universe.

If sugar precursors are common in space, then the ingredients for life might be common too. Not life itself, but the stuff life is made of. That shifts the question from "Are we alone?" to "How many places have the right conditions to assemble these ingredients into something living?"

What the Study Does Not Prove

This Is Not a Detection of Life

Let us be clear about what Rivilla and his team found. They found a molecule. A simple organic molecule with six atoms. That is a long way from finding a cell, or even a self-replicating RNA strand. The leap from (Z)-1,2-ethenediol to life is enormous, and most of the steps in between are still unknown.

The authors do not claim otherwise. They describe their detection as a "key intermediate" in sugar formation (Rivilla et al., 2022). That is precise and honest. It is one step in a long chain.

The Reaction Is Hypothetical

The proposed pathway from (Z)-1,2-ethenediol to glyceraldehyde is based on quantum chemical calculations and laboratory experiments. It has not been observed in space. The team detected the enol, and they detected glyceraldehyde in the same cloud. But they did not catch the reaction happening. That would require a different kind of observation, one that tracks the molecules over time, which is not possible with current telescopes.

So the connection is plausible, but it is not proven. The authors are careful to say "we propose" and "might be an important precursor" (Rivilla et al., 2022). That is the language of science, not certainty.

Other Pathways Exist

Glyceraldehyde can also form through other reactions, some of which do not involve (Z)-1,2-ethenediol at all. The formose reaction, for example, works in the lab under simulated interstellar conditions, even if it is less efficient. The presence of the enol does not rule out these other routes. It just adds another option.

The real value of the detection is that it shows nature is not limited to one chemical path. It takes every available route, and the more routes there are, the more likely it is that sugars form wherever conditions allow.

What This Actually Means

• ▸The detection of (Z)-1,2-ethenediol in the G+0.693-0.027 molecular cloud provides direct evidence that sugar precursors can form in interstellar space, not just on planetary surfaces. This means the chemical building blocks of RNA may be synthesized continuously throughout the galaxy and delivered to planets via meteorites or comets.

• ▸The abundance ratio of glycolaldehyde to (Z)-1,2-ethenediol (5.2 to 1) suggests that the enol form is being actively produced, not just surviving as a relic. This implies that the interstellar medium is a dynamic chemical factory, not a static freezer.

• ▸The proposed formation of glyceraldehyde from (Z)-1,2-ethenediol and the hydroxymethylene radical offers a new pathway to three-carbon sugars that does not require liquid water or catalysts. This expands the range of environments where prebiotic chemistry can occur.

• ▸The detection was made using radio astronomy, a technique that can identify specific molecules by their rotational spectra. This method is not limited to our galaxy. It can be applied to other star-forming regions, meaning we can map the distribution of sugar precursors across the Milky Way and beyond.

• ▸The existence of (Z)-1,2-ethenediol in space does not prove that life is common, but it does prove that the chemical steps toward life are common. The question is no longer whether the ingredients can form, but whether they can assemble into something replicating. That is a question for the next generation of telescopes and the next decade of experiments.