JWST reveals a low-metallicity atmosphere for giant planet TOI-5293 A b around a variable red dwarf

Star system: TOI 5293 A | Distance from the Sun: 529 light years

TOI-5293 A b is a giant planet about half the mass of Jupiter, orbiting an early red dwarf star every three days. The planet’s atmosphere was studied using two transits observed by the James Webb Space Telescope (JWST). The host star’s surface changes rapidly, making it challenging to interpret the data. In the first transit, the planet crossed regions of the star with different brightness, which contaminated the spectrum. The second transit allowed astronomers to model and remove these effects, providing a clearer view of the planet’s atmosphere.

Analysis of the uncontaminated spectrum shows that TOI-5293 A b has a low atmospheric metallicity—less than the Sun’s—along with a slightly higher carbon-to-oxygen ratio. The data strongly indicate the presence of methane, and also suggest traces of carbon dioxide, water, and ammonia. The planet’s radius is larger than expected for its temperature, making it difficult to determine its internal composition. This study highlights the importance of accounting for stellar variability when characterizing exoplanet atmospheres, especially around active red dwarfs.

Key findings
- TOI-5293 A b orbits a rapidly changing red dwarf star every three days
- JWST observations reveal a low-metallicity atmosphere and a slightly super-solar carbon-to-oxygen ratio
- Methane is strongly detected, with hints of carbon dioxide, water, and ammonia
- The planet’s radius is inflated compared to theoretical predictions
- Stellar variability must be carefully modeled to accurately study exoplanet atmospheres

Scientific study

GEMS JWST: A sub-Solar metallicity atmosphere for giant planet TOI-5293Ab orbiting a rapidly changing M-dwarf (external link)