For the past 20 years, scientists have been puzzled by two mysteries: first, there’s less sulfur in dense clouds and star-forming regions than in the spaces between stars, making it seem like sulfur is disappearing; and second, an unexplained peak appears in the infrared light from these regions.
An international team led by Leiden University astronomers now suggests that ammonium hydrosulfide salt could solve both mysteries.
According to their new study, sulfur can bind with ammonium under icy cosmic conditions and form a salt that sticks to dust and pebbles. The sulfur salt helps explain the mystery of the missing sulfur gas and a puzzling peak in data from the James Webb Space Telescope’s MIRI instrument and other telescopes.
The research was sparked by findings from ESA’s Rosetta mission, where a spacecraft orbited comet 67P between 2014 and 2016. Analyses published in late 2022 revealed that the comet’s dust particles had unexpectedly high levels of ammonium hydrosulfide.
For this study, the team simulated cosmic conditions in a laboratory. These conditions involve extremely cold conditions in which dust, ice, and pebbles are present, and relatively few molecules can react.
In experiments, they found that volatile NH3 (ammonia, well-known from detergents) and volatile H2S (hydrogen sulfide, the smell of rotten eggs) immediately react with ice around dust particles and form NH4SH (ammonium hydrosulfide salt). This means that dust and pebbles in dense star-forming regions trap some of the volatile sulfur.
As a result, the sulfur has disappeared.
The experiments also showed that ammonium hydrosulfide salt creates a peak at the exact location as the unexplained peak in data from the MIRI instrument on the James Webb Space Telescope. This discovery allowed astronomers to calculate that up to 20% of the missing sulfur could be in this salt on dust and pebbles.
Killing two birds with one stone
Katie Slavicinska, a PhD student at Leiden University and first author of the scientific paper, said, “I think it is great that we are finally unraveling both mysteries. With our research, we are killing two birds with one stone.”
Second author Adwin Boogert, a Dutch scientist at the University of Hawaii at Manoa, says: “It’s exciting to see how we can increasingly follow chemical traces back from our current solar system to the origin of new solar systems.”
Scientists are now looking forward to making more observations to confirm the infrared peak’s theory and find the remaining eighty percent of the missing sulfur.
Journal Reference:
- K. Slavicinska, A.C.A. Boogert, Ł. Tychoniec, E.F. van Dishoeck, M.L. van Gelder, M.G. Navarro, J.C. Santos, P.D. Klaassen, P.J. Kavanagh & K.-J. Chuang. Ammonium hydrosulfide (NH4SH) is a potentially significant sulfur sink in interstellar ice. Astronomy & Astrophysics. DOI: 10.1051/0004-6361/202451383
Source: Tech Explorist
