The latest discovery at the heart of our galaxy further reinforces the similarity between the Milky Way and a delicious treat. Previously, scientists identified a complex ester known as ethyl formate drifting among stars in the inner regions of the galaxy—a compound that gives raspberries their signature flavor. Now, astronomers have likely found sugar to sprinkle on this cosmic dessert.
In roughly the same area of space, researchers have pinpointed erythrulose—the first genuine sugar ever detected in interstellar space.
It’s unlikely anyone would want to eat it. Erythrulose is certainly edible, but it is mixed with a host of cosmic substances that are far less compatible with life (hello, cyanide-containing molecules). Fortunately, what wouldn’t work as a snack under normal circumstances could serve as an excellent ingredient for the emergence of life.
According to a research team led by astrochemist Izaskun Jiménez-Serra from the Spanish Center for Astrobiology, this finding may help clarify where the first biologically important sugars originated before life arose on Earth.
“A central question in origin-of-life research is how monosaccharides formed on primitive Earth, given that laboratory experiments under prebiotic conditions yield insufficiently high concentrations,” the researchers write in a new paper published in Nature Astronomy. “Interstellar erythrulose could have contributed to the pool of sugars available for early metabolic and replication processes.”
Life as we know it depends on sugars—small carbon-based molecules that cells use for energy and as building blocks for larger biological molecules. Sugars also form the backbone of RNA and DNA.
Sugars play a central role in prebiotic chemistry—the chemical conditions that lead to the emergence of life. However, because scientists still do not know how the first sugars formed, they are often treated simply as starting ingredients in prebiotic chemistry models.
We have evidence suggesting the possibility of sugar formation in cosmic environments. Sugars have been found in meteorites and samples from asteroid Bennu. Simple sugar precursors, such as glycolaldehyde and (Z)-1,2-ethenediol, have also been detected in space.
However, to find a true sugar containing three or more carbon atoms, researchers proposed looking at the galactic center.
The inner region of our galaxy is known as the Central Molecular Zone, filled with dense clouds of gas and dust rich in complex organic molecules.
The team directed two radio telescopes in Spain toward a particularly promising cloud called G+0.693, which has previously yielded other prebiotic molecules.
The search was conducted by detecting a unique radioactive signature of erythrulose. Each molecule rotates in its own distinctive way, producing a characteristic radio frequency spectrum that astronomers can identify even thousands of light-years away.
The G+0.693 region provided the team with what they were looking for—but the story had an unexpected twist, and not just because erythrulose is chiral. They anticipated that simpler three-carbon sugars would dominate.
Instead, the four-carbon sugar erythrulose appeared to be at least 8 to 17 times more abundant in the cloud than the three-carbon sugars glyceraldehyde and dihydroxyacetone, which were not detected at all.
This could be key information that reveals how sugars form in the interstellar medium. Computer models created by the researchers suggest that sugar forms on icy surfaces of tiny dust particles drifting through space.
On these grains, two relatively common two-carbon molecules—glycolaldehyde and ethylene glycol—can be activated by radiation and combine to form erythrulose.
Ultimately, shock waves may knock these molecules off dust particles and send them back into space, where telescopes can detect them.
The modeled abundances of these molecules do not exactly match the observed values, but there could be many reasons for this. Further studies may help uncover the causes of this discrepancy.
But there is another cherry on top of this interstellar cake. Erythrulose, consisting of 14 atoms, is the largest molecule ever detected in interstellar space that lacks closed rings in its structure, and only the second chiral molecule.
This suggests that the interstellar medium—and particularly the Central Molecular Zone—may be capable of far more complex chemical processes than we previously thought.
Moreover, this discovery could provide clues to how similar chemical processes might have existed in the cloud from which the Sun and all its planets formed.
As the researchers write, this discovery “not only provides direct evidence that complex chiral compounds can form in interstellar conditions, but also moves us to a higher level on the ladder of interstellar chemical complexity, suggesting that other prebiotic (and potentially chiral) molecules may also form and survive in the extreme conditions of the interstellar environment.”
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