Scientists have discovered the largest organic molecule containing sulfur ever identified in interstellar space, marking a breakthrough in understanding the chemical precursors of life beyond Earth. The molecule, named 2,5-cyclohexadiene-1-thione, is composed of carbon, hydrogen, and sulfur and contains 13 atoms, surpassing previously known sulfur-bearing molecules that typically had three to nine atoms. Researchers describe the finding as a “missing link” in tracing how complex, life-related chemistry emerges in the cosmos.
Sulfur, the 10th most abundant element in the universe, plays a critical role in amino acids, proteins, and enzymes, all essential for life on Earth. While simpler sulfur compounds had been detected in comets and meteorites, large sulfur-bearing molecules remained elusive in interstellar space, puzzling scientists. Mitsunori Araki, lead author of the study published in Nature Astronomy, explained:
“Sulfur came to Earth from space long ago, but we have only found a limited number of sulfur-bearing molecules in interstellar clouds. It should exist in huge amounts, but it is extremely difficult to detect.”
The discovery fills a critical gap in understanding the transition from simple interstellar molecules to the complex organic building blocks eventually delivered to Earth via comets and meteorites. “This is the largest sulfur-containing molecule ever found in space,” Araki added, “and it suggests that many more, perhaps even larger molecules, could exist undetected.”
The molecule was detected in a molecular cloud known as G+0.693–0.027, located about 27,000 light-years from Earth near the Milky Way’s center. Molecular clouds are cold, dense regions of dust and gas where new stars and planetary systems are born. Valerio Lattanzi, co-author of the study, described these clouds as cosmic laboratories:
“The ingredients embedded in molecular clouds are transferred to planets as they form. We are trying to understand how simple molecules evolve into the building blocks of life, adding each element to the picture one by one.”
The team first synthesized the molecule in the lab using thiophenol, a sulfur-containing liquid, and obtained a radio fingerprint for comparison with telescope observations from the IRAM-30m and Yebes radio telescopes in Spain. This allowed them to confirm the molecule’s presence in the interstellar cloud.
Experts hailed the discovery as a milestone in astrochemistry. Kate Freeman, a geosciences professor at Penn State University, called it “an exciting detective story made possible by powerful radio telescopes and a well-planned search strategy.” The detection of such molecules provides insight into how complex sulfur compounds found in meteorites could have originated outside our solar system, potentially seeding early Earth with life-essential chemistry.
Sara Russell, planetary sciences professor at the Natural History Museum in London, highlighted sulfur’s importance for early life:
“Sulfur is one of six elements critical to life on Earth and may have fueled ancient microbes. Finding complex organic molecules so far from Earth implies that the ingredients for life may be widespread across the galaxy.”
Ryan Fortenberry, a chemistry professor at the University of Mississippi, emphasized sulfur’s unique chemical properties, stating that the element allows molecules to achieve complexity beyond what carbon, oxygen, or nitrogen alone can provide.
Over the past 50 years, detections of molecules in space have evolved from rare, miraculous events to routine observations, revealing that interstellar chemistry is far richer than previously imagined. The discovery of 13-atom sulfur molecules reinforces the idea that life’s chemical precursors are resilient and abundant, raising the possibility that amino acids and other complex organics exist in star-forming regions well beyond our solar system.
As telescopes and observational methods continue to improve, researchers anticipate uncovering even larger, more complex molecules, bringing science closer to answering one of humanity’s oldest questions: how life begins and where else it might exist in the universe.