JWST reveals muted water and carbon dioxide features in the atmosphere of hot Jupiter NGTS-2 b

Star system: NGTS-2 | Distance from the Sun: 1175 light years

NGTS-2 b is a hot Jupiter with a temperature of about 1,470 Kelvin, orbiting an F-type star in an orbit aligned with the star’s spin. Using the James Webb Space Telescope (JWST), astronomers observed a transit of NGTS-2b and measured its atmosphere’s spectrum from 2.84 to 5.18 micrometers. The spectrum shows weak absorption features from water and carbon dioxide, but the data are not sufficient to precisely determine the planet’s atmospheric composition.

The analysis found that the best-fitting models require high water content, but some solutions suggest more water than is physically possible, likely due to degeneracies between cloud properties and metallicity, as well as limited wavelength coverage. The results also hint at a subsolar carbon-to-oxygen ratio and supersolar metallicity, but the uncertainties are large. The study highlights the challenges of interpreting exoplanet spectra when the data are limited and shows that more observations across a wider range of wavelengths are needed to resolve these ambiguities.

Key findings
- JWST observed a muted transmission spectrum for NGTS-2 b, with weak water and carbon dioxide features
- Some model solutions require unrealistically high water content due to degeneracies in the data
- The best-fitting models hint at a subsolar C/O ratio and supersolar metallicity, but with large uncertainties
- The presence of sulfur monoxide is suggested by only two data points and is likely not real
- Broader wavelength coverage is needed to better constrain the planet’s atmospheric properties

Scientific study

BOWIE-ALIGN: Exploring degeneracies in the muted transmission spectrum of the aligned hot Jupiter NGTS-2b with NIRSpec/G395H (external link)