The discovery stands out because astronomers had previously only identified relatively small sulfur compounds in space, typically with six atoms or fewer. Sulfur plays an essential role in proteins and enzymes on Earth, so scientists have long suspected that larger sulfur-bearing molecules should exist in the interstellar medium. Until now, however, this class of molecules had remained missing from radio surveys, creating a gap between simple sulfur chemistry in space and the complex organic inventory measured in comets and meteorites.

The team reports that the newly detected C6H6S is structurally related to molecules recovered from extraterrestrial samples within our own solar system. As a result, it provides a direct chemical bridge between the molecular content of a starless interstellar cloud and the materials incorporated into comets and meteorites. This bridge strengthens the idea that some of the building blocks of life may be assembled long before planets form.

To find the molecule, the researchers first had to create and characterize it in the laboratory. They synthesized 2,5-cyclohexadiene-1-thione by applying a 1,000 volt electrical discharge to liquid thiophenol (C6H5SH), a substance noted for its strong odor. Using a self-developed laboratory spectrometer, they then measured the molecule's radio emission frequencies with very high precision, establishing a unique spectral fingerprint with more than seven significant digits.

Armed with this fingerprint, the team searched through existing astronomical survey data of the molecular cloud G+0.693-0.027. The observations, collected with the IRAM 30 meter and Yebes 40 meter radio telescopes in Spain, contained a forest of spectral lines from many different molecules. By matching the laboratory spectrum of C6H6S to lines in the cloud's radio emission, the scientists were able to identify the molecule's presence and determine that it is abundant enough to be detected clearly.

According to the researchers, the detection of a 13 atom sulfur-bearing ring molecule in a young, starless molecular cloud shows that complex chemistry is already underway before stars and planetary systems emerge. They argue that this is evidence that the chemical groundwork for life, including key sulfur-containing organics, can originate in the cold, dense regions of interstellar space. Such regions later collapse to form stars and planetary systems, potentially carrying this preassembled chemistry into new environments.

The result implies that many additional complex sulfur compounds may be hiding in interstellar spectra, still unassigned because their laboratory fingerprints are not yet available. Extending laboratory spectroscopy to other sulfur-bearing ring systems and related molecules could therefore reveal a richer inventory of prebiotic chemistry in space. The authors see this as an important step toward connecting interstellar molecules, cometary materials and the emergence of biochemistry on young planets.

Research Report:Sulfur-Bearing Cyclic Hydrocarbons in Space

Related Links
Max Planck Institute for Extraterrestrial Physics
Stellar Chemistry, The Universe And All Within It