Sulfur in the Clouds: Webb Spies a Super-Neptune's Atmosphere ⚡ экспресс
Using transmission spectroscopy with JWST (NIRSpec G395H) during a single transit, the atmosphere of exoplanet HAT-P-26 b (mass ~18.6 M⊕, radius ~6.33 R⊕) was studied. Water vapor (ln B = 4.1), carbon dioxide (ln B = 85.6), and sulfur dioxide (ln B = 13.5) were detected with high confidence, along with weak hints of hydrogen sulfide and carbon monoxide (ln B < 0.5). The detection of SO₂ on a warm super-Neptune fills the gap between previous detections on hot Jupiters and sub-Neptunes, demonstrating the role of non-equilibrium photochemistry in planetary atmospheres with temperatures below 1000 K. The measured abundances of carbon, oxygen, and sulfur indicate a metallicity around 10 times solar and a sub-solar C/O ratio. Retrieved molecular abundances within 2σ are consistent with self-consistent photochemical models. The enhanced CO₂ abundance and potential H₂S signal are sensitive to thermal structure, clouds, or vertical mixing.
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.