Sulfur in the Clouds: Webb Spies a Super-Neptune's Atmosphere ⚡ экспресс
Using the James Webb Telescope, scientists obtained a transmission spectrum (analysis of light filtered through the atmosphere) of planet HAT-P-26 b—a warm super-Neptune. Water vapor, carbon dioxide, and sulfur dioxide were confidently detected, with hints of hydrogen sulfide and carbon monoxide. The presence of SO₂ on a planet cooler than 1000 K bridges the gap between hot Jupiters and smaller worlds, showing that non-equilibrium photochemistry operates across a wide range of conditions. Measurements indicate a metallicity around 10 times solar and a reduced carbon-to-oxygen ratio. It's like tasting an atmospheric “soup”: the abundance of ingredients tells us about the planet’s origins.
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.
🎯 Astronomers call all elements heavier than hydrogen and helium 'metals,' so carbon, oxygen, and sulfur are metals to them too.
🎬 In the series 'The Expanse,' characters scan the atmospheres of distant planets for signs of life; now, such diagnostics are a reality for dozens of worlds.