In the cloud of gas and dust where planets are born, sulfur is like a chef tasting a dish at different stages of cooking. At first, it's almost entirely in gas, like steam rising from a pot. Then, as the temperature drops, sulfur settles onto dust grains and turns into solid particles, just as steam condenses on a lid. A planet, gathering these particles, records in its composition the stage at which it caught them.

Previously, astronomers thought of sulfur only as a solid additive that enters planets along with rocks. But new research shows that sulfur can be both gas and solid, and its journey is more complex. The scientists built a computer model that tracked how sulfur moves from gas to dust and back, and how planets accumulate it. It turned out that giant planets like Jupiter can acquire a lot of sulfur not only from rocky debris, but also if they formed far from their star, beyond the line where hydrogen sulfide freezes into ice.

For rocky planets like Earth, the result is surprising: some are born with very little sulfur. And sulfur is important for life: it's a component of proteins and helps cells breathe. So a lack of sulfur could make a planet less habitable. Now, by looking at distant worlds, astronomers can use sulfur abundance to infer where and how these worlds formed, like a detective reconstructing a whole route from a crumb on the carpet.