JWST Finds Methane in Atmosphere of Temperate Exoplanet TOI-199 b

JWST Detects Methane in the Atmosphere of Temperate Saturn-Sized World TOI-199 b

WASHINGTON — Astronomers using NASA’s James Webb Space Telescope (JWST) have characterized the atmosphere of a rare exoplanet located roughly 330 light-years from Earth. The planet, TOI-199 b, is roughly the size of Saturn but features a remarkably mild equilibrium temperature of around 80°C (175°F)—making it significantly cooler than the scorching "hot Jupiters" usually studied by space telescopes.

Atmospheric Fingerprints Captured

Using transmission spectroscopy, the research team analyzed starlight filtering through TOI-199 b’s outer atmosphere as the planet transited its host star. The data revealed distinct spectral signals of methane ($\text{CH}_4$), along with potential signatures of carbon dioxide ($\text{CO}_2$) and ammonia ($\text{NH}_3$).

A Non-Biological Origin

Scientists caution that the presence of methane does not imply alien life. On gas giants like TOI-199 b—as well as Jupiter and Saturn in our own Solar System—methane is a natural byproduct of standard planetary formation and atmospheric chemistry.

A Milestone for Exoplanet Science

The discovery marks a major technical achievement. Analyzing the atmosphere of a world 330 light-years away using starlight as a backlight validates long-standing theoretical models of temperate gas worlds, proving that Webb can probe planets in thermal regimes far closer to familiar conditions than ever before.