JWST detects methane on temperate gas giant for first time

Friday 22 - 09:56

By: Dakir Madiha

JWST detects methane on temperate gas giant for first time

Astronomers have identified methane in the atmosphere of a temperate gas giant outside the solar system for the first time. The discovery comes from observations of TOI-199b, a Saturn-sized exoplanet located more than 330 light years from Earth. The planet sits in a rare temperature range of about 79 degrees Celsius, placing it between scorching hot gas giants and the colder worlds found in the outer solar system.

The planet completes an orbit around its host star in roughly 100 days. Researchers used transit spectroscopy to study its atmosphere while it passed in front of its star. During an extended 20-hour observation campaign, including a seven-hour transit window, the James Webb Space Telescope collected the data needed to analyze the planet’s atmospheric composition.

The resulting spectrum revealed clear absorption signals consistent with methane. Scientists also detected traces of ammonia and carbon dioxide. These chemical signatures align with long-standing theoretical models that predicted methane should be present in temperate gas giants, but until now no direct confirmation had been achieved for a planet in this category.

Researchers involved in the study said the findings strengthen confidence in current models of planetary atmospheres and formation. They noted that further observations could refine estimates of gas abundances and help determine whether TOI-199b represents a broader class of temperate gas giants or a rare exception. The results also offer new reference points for understanding atmospheric chemistry in distant worlds, including processes that may inform studies of planetary atmospheres closer to Earth.