Astronomers have harnessed spectral data from the Near Infrared Spectrometer (NIRSpec) on board the NASA/ESA/CSA James Webb Space Telescope to investigate the atmosphere of TOI-199b, a distant Saturn-mass exoplanet that is neither frigid nor scorching.
Artist’s impression of a gas giant exoplanet. Image credit: Sci.News.
TOI-199, a G-type star situated approximately 330 light-years away in the constellation Sera, hosts at least two massive planets: TOI-199b and TOI-199c.
The inner planet, TOI-199b, orbits its host star, receiving 2.5 times more radiation than Earth every 105 days, resulting in an estimated temperature of 352 K (79 degrees Celsius, or 174 degrees Fahrenheit).
With a mass of 0.17 times that of Jupiter and a radius of 0.81 times that of Jupiter, TOI-199b is inferred to have a Saturn-like internal structure and a hydrogen-rich atmosphere.
“TOI-199b is one of the most promising cold giant planets for atmospheric characterization,” stated Penn State astronomer Renyu Hu and colleagues.
Astronomers employed transmission spectroscopy to scrutinize light emitted from the star as it traversed the planet’s atmosphere, enabling the characterization of TOI-199b’s atmospheric composition.
“Our analysis revealed that the wavelengths of starlight absorbed by methane were blocked by the atmosphere,” explained Dr. Aaron Bello Alfe, a postdoctoral researcher at NASA’s Jet Propulsion Laboratory.
“Compositional models for temperate gas giant exoplanets indicated the likely presence of methane, so confirming this theory is a significant milestone.”
Webb’s observations also indicated that TOI-199b’s atmosphere contains ammonia and carbon dioxide in addition to methane.
“Further observations will enhance our understanding of the relative abundances of these gases,” noted Dr. Hu.
A comprehensive examination of temperate gas giants could refine our models and deepen our understanding of planetary formation and atmospheric evolution, including that of Earth.
“The success of this preliminary investigation encourages us to allocate more observational resources to study similar planets,” added the team.
This will enable us to determine whether TOI-199b is unique or if shared characteristics exist among planets of this type.
The team’s results were published in the May 20th issue of astronomy magazine.
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Aaron Bello-Alfe et al. 2026. Methane from the temperate exoplanet Saturn TOI-199b. A.J. 171,354; doi: 10.3847/1538-3881/ae4fba
Source: www.sci.news
