In the dark, cold clouds where stars are born, dust grains are covered with an icy crust. Across this crust, like on a winter road, individual atoms wander slowly. Calculations show that it is precisely these wandering oxygen and nitrogen atoms that kick off the assembly of the HNSO molecule — a compound of hydrogen, nitrogen, sulfur, and oxygen.
First, an oxygen or nitrogen atom bumps into a molecular fragment — the radical NS or SO. From these, a key piece emerges — the molecule NSO. Then NSO captures a hydrogen atom and turns into HNSO. In most cases, the resulting shape is bent, like the letter "C," while the linear form, like a straight stick, is short-lived and quickly falls apart.
In the gas phase, HNSO remains less abundant than OCS because it has a harder time leaving the ice. So, this molecule should be sought in the solid icy mantles of dust grains, not in the surrounding gas. Such wandering atoms on icy grains might also assemble other complex molecules that feature several different elements side by side.
HNSO is one of the few molecules where four different atoms (hydrogen, nitrogen, sulfur, and oxygen) are linked in a single chain. In space, such "mixed" molecules are rare, and each new find helps us understand how chemical diversity is built from simple atoms.