For decades, astronomers have been puzzled by a strange mystery in space: where is all the sulfur?
This element, essential for life on Earth and common in the universe, appears to be missing when scientists look for it in space.
Now, new research may have solved the puzzle—sulfur might be hiding in icy regions far from our sight.
An international team of scientists, including astrochemist Ryan Fortenberry from the University of Mississippi, chemist Ralf Kaiser from the University of Hawaii at Mānoa, and computational chemist Samer Gozem from Georgia State University, has published findings in Nature that could finally explain the shortage.
“Hydrogen sulfide is everywhere on Earth—it comes from volcanoes, affects ocean chemistry, and is even released from coal power plants,” Fortenberry said.
“If we understand sulfur’s chemistry better, it could open the door to new technologies. But first, we need to understand what it’s doing in space.”
Sulfur is the 10th most abundant element in the universe and plays an important role in planets, stars, and living organisms. Yet when astronomers measure sulfur in dense clouds of gas and dust—the birthplaces of stars—they find far less than expected, sometimes a thousand times less than predicted.
The team’s research points to interstellar ice as the hiding place. In the freezing depths of space, sulfur atoms can join together to form stable shapes. Some arrange into octasulfur crowns—rings made of eight sulfur atoms—while others form polysulfanes, long chains of sulfur atoms linked by hydrogen. These molecules can stick to icy dust grains, locking the sulfur away in solid form and making it invisible to standard telescopes.
“When we use telescopes like the James Webb Space Telescope, we see clear chemical fingerprints for oxygen, carbon, and nitrogen,” Fortenberry explained. “But with sulfur, something doesn’t add up. We think the most common sulfur forms—crowns and chains—are hiding in the ice.”
Laboratory experiments simulating the extreme cold of space support this idea. The team created conditions similar to those in interstellar space and showed that sulfur-rich molecules could indeed form on icy surfaces. These molecules would stay frozen until warmed in star-forming regions, at which point they could evaporate into gas and be detected by radio telescopes.
One reason sulfur is hard to track is that it constantly changes its structure. “It never stays the same—it shifts from crowns to chains and other shapes,” Fortenberry said. “It’s a bit like a virus, changing as it moves.”
By identifying the stable forms that sulfur can take in ice, the researchers have given astronomers a new target for their searches. If confirmed, this discovery could solve a long-standing space mystery and deepen our understanding of the chemistry that shapes planets, stars, and possibly life itself.
“What I love about astrochemistry is that it forces us to ask big, hard questions,” Fortenberry said. “And when we look for answers, we sometimes find solutions that have benefits far beyond what we expected.”
Source: University of Mississippi.
