When starlight passes through a planet's atmosphere, it's as if it's sifted through a sieve: different gases filter out specific colors. By catching these leaks, the James Webb telescope identifies the chemical makeup like a connoisseur discerning a dish's ingredients by its aroma. This transit spectroscopy method was first used by David Charbonneau.

The exoplanet HAT-P-26 b turned out to be a veritable cosmic kitchen. In its air, Webb found water and carbon dioxide, but the key ingredient was sulfur dioxide — the very stuff that gives burnt matches their smell. Before, SO₂ was only 'cooked up' in the hellish heat of hot Jupiters or chilly sub-Neptunes, but now it's been spotted in lukewarm temperatures for the first time. This means the star's ultraviolet light runs the kitchen on planets cooler than 1000 °C.

A surprising twist: the amount of sulfur dioxide follows a strict recipe — the higher the metallicity (abundance of heavy elements), the more SO₂, but only up to 30 times the Sun's value; then the burner nearly shuts off. Theorists had predicted such a rich brew.