Hidden in Cosmic Ice: Scientists Track Down Missing Sulfur in Space

Sulfur, the 10th most abundant element in the universe, is expected to be present in large amounts within dense molecular clouds. Yet observations consistently show sulfur levels that are thousands of times lower than predicted.

To solve this mystery, an international team of researchers, including Ryan Fortenberry, an astrochemist at the University of Mississippi; Ralf Kaiser, professor of chemistry at the University of Hawaii at Mānoa; and Samer Gozem, computational chemist at Georgia State University recreated the extreme cold conditions of interstellar space in the laboratory. Their experiments revealed that in cold regions of space, sulfur can assemble into stable molecular shapes, such as crown-like rings of eight atoms (known as octasulfur, or S₈) and long hydrogen-linked chains called polysulfanes. These structures can form on icy dust grains, trapping sulfur in solid form and keeping it hidden from conventional detection methods.

“Instruments like the James Webb Space Telescope give us clear signals for elements such as oxygen, carbon, and nitrogen,” said Ryan Fortenberry, an astrochemist at the University of Mississippi. “But sulfur has always been an outlier. What our work shows is that the most common forms of sulfur we already know on Earth may also exist in space—just frozen into ice and difficult to see.”

The team’s findings suggest that sulfur is not truly missing, but rather hiding in plain sight. Once these icy grains heat up in star-forming regions, the sulfur molecules may sublimate into gas, where radio telescopes could finally detect them.

“This research provides a road map for astronomers to track sulfur in the cosmos,” explained Ralf Kaiser. “By identifying these stable molecular configurations in the lab, we can now guide observations and test whether they exist in interstellar space.”

Because sulfur atoms are constantly shifting between crowns, chains, and other shapes, they have been especially difficult to pin down. “It never maintains the same structure—it’s a moving target,” Fortenberry said.

The discovery deepens our understanding of how essential elements for life are distributed across the universe.

Sources: 

Science Daily

The University of Mississippi

DOI: 10.1038/s41467-025-61259-2