Scientists have identified the largest organic molecule containing sulfur yet observed in interstellar space — a 13-atom compound that researchers say helps bridge the gap between simple cosmic chemistry and the complex organics found in comets and meteorites.
What Was Found: The molecule, 2,5-cyclohexadiene-1-thione, was detected in the dense molecular cloud G+0.693–0.027 near the center of the Milky Way, about 27,000 light-years from Earth. The discovery was reported in Nature Astronomy and led by Mitsunori Araki of the Max Planck Institute for Extraterrestrial Physics.
Extracted sulphur on Mount Ijen in Indonesia. Sulfur is a key ingredient for life. - Laura Portinaro/REDA/Universal Images Group/Getty Images
Why Sulfur Matters: Sulfur is the 10th most abundant element in the universe and a key component of amino acids, proteins and many enzymes on Earth. Until now, astronomers had found mostly small sulfur-bearing molecules in interstellar space (typically 3–5 atoms), with the previous largest example containing nine atoms. Finding a 13-atom sulfur-bearing organic significantly expands the known chemical complexity available in molecular clouds.
“Sulfur came to Earth from space long, long ago,” said Mitsunori Araki. “We have only found a very limited amount of sulfur-bearing molecules in space, which is strange. It should exist in huge amounts, but it’s very difficult to find.”
Molecular clouds, such as the Sagittarius B2 molecular cloud seen here, act as stellar nurseries. - NASA, ESA, CSA, STScI, Adam Ginsburg (University of Florida), Nazar Budaiev (University of Florida), Taehwa Yoo (University of Florida), Alyssa Pagan (STScI)
How the Detection Was Confirmed: The research team produced the molecule in the laboratory by applying an electric discharge to thiophenol, yielding a precise radio-frequency signature — a radio “fingerprint.” They matched that laboratory spectrum to archival radio observations of G+0.693–0.027 taken with the IRAM-30m and Yebes radio telescopes in Spain, confirming the molecule’s presence in space.
Implications for Origins of Life: The detection helps fill a long-standing gap between the simple molecules observed in the interstellar medium and the more complex sulfur-rich organics recovered from comets and meteorites. Scientists believe some of those complex compounds were delivered to early Earth by impacts, helping set the stage for prebiotic chemistry and early microbial life.
Study authors Christian Endres (left) and Mitsunori Araki work on an experiment in the lab. - MPE
“A molecular cloud is where star formation is happening,” said Valerio Lattanzi, coauthor of the study. “The ingredients embedded in the cloud will be transferred to planets. We are trying to find out which ingredients can eventually form life, and to add elements to this picture one by one.”
Expert Reactions: Independent researchers praised the result. Kate Freeman of Penn State called the work an “exciting detective story” enabled by powerful radio telescopes and a focused search strategy. Sara Russell of the Natural History Museum in London noted that sulfur is one of six elements essential to life and said the finding makes biologically relevant materials appear more widespread. Ryan Fortenberry of the University of Mississippi emphasized sulfur’s unique chemistry and predicted future detections likely will include even larger organics and, eventually, amino acids beyond our solar system.
Looking Ahead: The discovery adds to a catalog of more than 300 molecules observed in space and suggests that many more, possibly larger, sulfur-bearing compounds remain to be found. Continued laboratory spectroscopy combined with deep radio surveys will help reveal the chemical richness of molecular clouds and their role in seeding planets with life’s raw materials.
