WASP-121b's transmission spectrum observed with JWST/NIRSpec G395H reveals thermal dissociation and SiO in the atmosphere
arXiv:2506.02199 · doi:10.3847/1538-3881/ad9c6e
Abstract
WASP-121b has been established as a benchmark ultrahot Jupiter, serving as a laboratory for the atmospheric chemistry and dynamics of strongly irradiated extrasolar gas giants. Here, we present and analyze WASP-121b's transmission spectrum observed with NIRSpec G395H on board the James Webb Space Telescope and find evidence for the thermal dissociation of HO and H on the planet's permanent dayside. Additionally, we detect SiO at a statistical significance of which is compatible with chemical equilibrium in the atmosphere. Constraining the abundance of SiO and abundance ratios between silicon and volatile atoms in WASP-121b's atmosphere could help discriminate between possible migration histories of the planet. The three-dimensional nature of thermal dissociation on WASP-121b's dayside and of recombination on its nightside, however, poses a challenge to constraining molecular abundances and elemental abundance ratios from the transmission spectrum. To account for this, we implemented an atmospheric model in the NEMESIS framework that splits the planet's atmosphere into dayside and nightside. A retrieval applying our atmospheric model to WASP-121b's transmission spectrum favors a higher HO abundance on the nightside than on the dayside, demonstrating the impact of hemispheric heterogeneity when attempting to constrain WASP-121b's bulk HO inventory.
26 pages, 15 figures, 6 tables
References in corpus (24)
- Array Programming with NumPy
- The Astropy Project: Sustaining and Growing a Community-oriented Open-source Project and the Latest Major Release (v5.0) of the Core Package
- On the radiative equilibrium of irradiated planetary atmospheres
- Theoretical Spectra and Light Curves of Close-in Extrasolar Giant Planets and Comparison with Data
- An ultrahot gas-giant exoplanet with a stratosphere
- Fingering convection and cloudless models for cool brown dwarf atmospheres
- ExoMol line lists -- XXXIX. Ro-vibrational molecular line list for CO
- The Effects of Consistent Chemical Kinetics Calculations on the Pressure-Temperature Profiles and Emission Spectra of Hot Jupiters
- Hot Exoplanet Atmospheres Resolved with Transit Spectroscopy (HEARTS) IV. A spectral inventory of atoms and molecules in the high-resolution transmission spectrum of WASP-121 b
- The Stagger-grid: A grid of 3D stellar atmosphere models - IV. Limb darkening coefficients
- ExoMol molecular line lists V: The ro-vibrational spectra of NaCl and KCl
- Effects of a fully 3D atmospheric structure on exoplanet transmission spectra: retrieval biases due to day-night temperature gradients
- An emission spectrum for WASP-121b measured across the 0.8-1.1 micron wavelength range using the Hubble Space Telescope
- Analysis of a JWST NIRSpec Lab Time Series: Characterizing Systematics, Recovering Exoplanet Transit Spectroscopy, and Constraining a Noise Floor
- ExoMol line lists XXIV: A new hot line list for silicon monohydride, SiH
- Diurnal variations in the stratosphere of the ultrahot giant exoplanet WASP-121b
- Confirmation of water emission in the dayside spectrum of the ultrahot Jupiter WASP-121b
- Constraining mornings & evenings on distant worlds: a new semi-analytical approach and prospects with transmission spectroscopy
- UV Exoplanet Transmission Spectral Features as Probes of Metals and Rainout
- A JWST NIRSpec Phase Curve for WASP-121b: Dayside Emission Strongest Eastward of the Substellar Point and Nightside Conditions Conducive to Cloud Formation
- Phase curve pollution of exoplanet transmission spectra
- The PHOENIX Exoplanet Retrieval Algorithm and Using H Opacity as a Probe in Ultra-hot Jupiters
- Catwoman: A transit modelling Python package for asymmetric light curves
- ARES VI: Viability of one-dimensional retrieval models for transmission spectroscopy characterization of exo-atmospheres in the era of JWST and Ariel