Exoplanet Atmosphere Report · JWST NIRISS SOSS + NIRSpec G395H

WASP-96 b

The planet whose transmission spectrum NASA unveiled on 12 July 2022 as JWST's first exoplanet result — a clear water-vapor detection that became one of the most recognized plots in the mission's history. This page works from that reduced data, plus a later analysis of its morning and evening terminators.

Transit-discovered, 2014 NASA Exoplanet Archive parameters JWST reduced spectra (2 instruments)
Artist's concept of the hot Saturn WASP-96 b

AI-generated artist's concept of WASP-96 b — not a real photograph. All data and figures in this report come from actual JWST NIRISS SOSS and NIRSpec G395H observations (see below).

The planet, in numbers

Queried live from the NASA Exoplanet Archive TAP service (pscomppars).

Radius13.45 Earth radii (~1.20 Jupiter radii)
Mass152.6 Earth masses (~0.48 Jupiter masses)
Orbital period3.43 days
Semi-major axis0.045 AU
Equilibrium temperature1285 K
Host starWASP-96, G-type dwarf, Teff = 5540 K, 1.05 Rsun, 1.06 Msun
Distance352.5 parsecs (~1150 light-years)
Discovery2014, transit photometry (WASP survey)

Why this planet made history

WASP-96 b is a "textbook" hot Saturn: hot enough for a clear, largely cloud-free atmosphere, orbiting a bright, quiet host star, with a large predicted atmospheric signal. Those three properties made it the ideal target to demonstrate JWST's transmission-spectroscopy capability to the public, and its NIRISS SOSS spectrum — showing an unmistakable water absorption feature near 1.4 microns — was the first exoplanet result released from the telescope.

A later analysis combined VLT/FORS2, NIRISS/SOSS, and NIRSpec/G395H. Multi-code retrievals strongly detect H2O, CO2, and Na; self-consistent grids favour 2–6× stellar metallicity, while SO2 receives only moderate support (ln B = 2.69). The authors also searched both JWST datasets for wavelength-dependent differences between the morning and evening terminators.

Close-up 3D-rendered concept of WASP-96 b's cloud-free, water-vapor-bearing atmosphere

AI-generated 3D-render-style concept of WASP-96 b — not an actual image of the planet.

Complete spectrum hierarchy and limb audit

The supplementary archive contains 12 transmission products rather than two: symmetric spectra at several resolutions and separate NIRISS and NIRSpec morning/evening fits. The figure keeps the broad spectrum, fitted hemisphere parameters, and wavelength-dependent limb difference distinct.

Four-panel WASP-96 b spectrum hierarchy and limb-asymmetry evidence audit
A: 0.6–5.2 µm spectrum. B–C: archived NIRISS and NIRSpec hemisphere parameters. D: wavelength-dependent differences after removing each instrument's constant offset. Generated by scripts/analyze_spectrum.py.
Source products12
NIRISS constant offset−3.40 diagonal σ
Water-band, marginal errors0.78 diagonal σ
Published injection test2.6σ tentative

The CSVs cannot independently reproduce the paper's limb-asymmetry significance. Adding the released marginal morning/evening errors in quadrature gives a 0.78σ water-band difference; the source study's 10,000 uniform-planet light-curve simulations give 2.6σ. The limb parameters are jointly fitted, but their covariance is not released in these tables. Therefore the diagonal calculation neither validates nor overturns the injection/recovery result. The scientifically supported conclusion remains tentative—not zero, and not conclusive.

The −3.40σ diagonal NIRISS mean offset is a wavelength-independent nuisance diagnostic and is degenerate with transit mid-time; it must not be presented as atmospheric structure. NIRSpec's corresponding mean ratio is 0.04σ. The analysis removes these constant offsets before inspecting wavelength-dependent residual structure.

Data and method notes

All 12 spectrum products are copied from Zenodo 17065171 with original headers and missing edge bins preserved. The source manifest records the 132 MB archive MD5 and a cross-platform subset hash. Reproduce with python scripts/validate_sources.py and python scripts/analyze_spectrum.py; download the structured summary, resolution inventory, and bin-level limb differences.

AI-generated illustration of the James Webb Space Telescope

AI-generated illustration of the James Webb Space Telescope, whose NIRISS and NIRSpec instruments took the real spectra used in this report. Not an official mission photograph — see NASA/JWST for real imagery.

References

  1. JWST Early Release Observations Team, 2022. Webb Reveals Steamy Atmosphere of Distant Planet in Detail. NASA press release, 12 July 2022 (first published JWST exoplanet transmission spectrum, WASP-96 b, NIRISS SOSS).
  2. Radica, M. et al., 2026. Super-Solar Metallicity and Tentative Evidence for Photochemistry on WASP-96 b from JWST and Ground-Based VLT Transmission Spectroscopy. Accepted to The Astronomical Journal; arXiv:2604.05049.
  3. Complete supplementary archive: Zenodo record 10.5281/zenodo.17065171.
  4. Hellier, C. et al., 2014. WASP-95b and WASP-96b: two new transiting close-in giant planets. Monthly Notices of the Royal Astronomical Society, 440(2), pp.1982-1992 (discovery paper).
  5. NASA Exoplanet Archive, exoplanetarchive.ipac.caltech.edu — system parameters, queried live via TAP.