Inflated hot Jupiter · dayside emission · JWST + TESS

WASP-17 b

An exceptionally inflated giant planet examined through a corrected TESS transit and three independent reductions of its JWST/NIRISS dayside emission spectrum.

REAL TESS DATATIMING-AWARE FITPUBLIC SPECTRUMTESTED PIPELINE

AI-generated artist’s interpretation · not a direct image

What the corrected fit shows

Transit supportSUPPORTED (ΔBIC ≥ 10)
Fitted midpoint shift+1.444 h
Model depth16785.5 ± 100.3 ppm
ΔBIC (null − transit)30092.5

The timing-adjusted transit is strongly preferred by ΔBIC = 30092.5. Its fitted midpoint is +1.444 hours from the historical prediction; the model's mid-transit depth is 16785.5 ± 100.3 ppm. The support decision uses ΔBIC ≥ 10; timing-search p-values are not presented as blind-detection probabilities.

Timing-adjusted limb-darkened transit fit for WASP-17 b
The dotted vertical line is the historical archive prediction; the dashed colored line marks the fitted midpoint (+1.444 h). The smooth curve fits timing, radius ratio, impact parameter, and a local linear baseline.

Explicit model comparison

Linear nullχ² 34111.14 / 4042 dof

BIC = 34127.75

Limb-darkened transitχ² 3993.76 / 4039 dof

BIC = 4035.28

The null fits a local intercept and slope. The transit adds bounded midpoint, radius-ratio, and impact-parameter freedom while retaining the same baseline terms. Fixed limb darkening and circular geometry make this a diagnostic fit rather than a full system retrieval.

Multi-sector robustness and noise

Supported combined depth16828.0 +/- 89.3 ppm
Supported / fitted sectors2 / 2
Residual beta range1.28-1.46

The archive prediction was timing-adjusted independently in 2 fitted sector(s) (S12, S38), of which 2 meet Delta BIC >= 10. Formal depth errors were inflated by sqrt(max(reduced chi-square, 1)) times the residual time-averaging beta factor (observed range 1.28-1.46). The robust inverse-variance model depth across supported sectors is 16828.0 +/- 89.3 ppm; Cochran Q = 0.14 for 1 dof (p = 0.7131). These scaled errors address underestimated scatter and short-timescale correlation, but they are not a full Gaussian-process or physical limb-darkened transit fit.

Independent sector transit fits for WASP-17 b
Independent sector transit fits. Reproduced from the committed public TESS SPOC files.
Sector depth consistency for WASP-17 b
Sector depth consistency. Reproduced from the committed public TESS SPOC files.
Residual RMS time-averaging diagnostic for WASP-17 b
Residual RMS time-averaging diagnostic. Reproduced from the committed public TESS SPOC files.

Published planetary spectrum

Three independent published NIRISS/SOSS reductions are plotted and tested against their own weighted-flat spectra. Showing all reductions makes pipeline-dependent scatter visible; no molecular abundance is inferred from these flatness tests.

Published emission spectrum of WASP-17 b
JWST NIRISS/SOSS emission data from 10.5281/zenodo.14003330. Exact files and checksums are in data/SOURCE.md; numerical tests are in spectrum_statistics.csv.

Atmospheric evidence: detection, limit, or unknown?

All three archived reductions reject a wavelength-independent dayside spectrum. The molecular attribution is taken from the paper's atmospheric retrieval rather than inferred from the flat-spectrum test reproduced here.

Source-graded atmospheric evidence
Literature evidence is kept separate from calculations reproduced in this repository.
SpeciesStatusEvidenceBasis
H2Oreported detection6.4 sigmapeer-reviewed/preprint retrieval
CO / CO2not established hereno repository retrievalwavelength structure alone is non-specific
O2no evidencenot reportedno molecular-oxygen inference

Primary source: Gressier et al. 2024, JWST-TST DREAMS. Oxygen-bearing molecules are not detections of molecular oxygen (O2) and are not, by themselves, biosignatures.

The system

Radius20.96 Earth radii
Mass247.91 Earth masses
Orbital period3.735430 days
Transit duration4.423 hours
Semi-major axis0.0515 AU
Equilibrium temperature1755 K
Host and distanceWASP-17 · 405.91 pc
Discovery2009 · Transit · SuperWASP

Values are from the exact saved NASA Exoplanet Archive pscomppars row in data/system_parameters.csv.

Data and reproducibility

The observed photometry is the public MAST file tess2019140104343-s0012-0000000066818296-0144-s_lc.fits, TESS Sector 12, collection DOI 10.17909/t9-nmc8-f686. It is stored unmodified. Exact archive URI, URL, retrieval date, and checksum are in data/SOURCE.md.

Run python scripts/analyze_transit.py and python scripts/analyze_multisector.py and python scripts/analyze_atmospheric_evidence.py plus python scripts/analyze_spectrum.py to regenerate the figures and CSVs, then pytest tests/ -v to check the documented values against the real file.

Limitations

  • The orbit is circular and the quadratic limb-darkening coefficients are fixed representative values.
  • The scaled semi-major axis comes from saved composite values whose uncertainties are not propagated.
  • The midpoint is searched within a bounded window; ΔBIC is used as the support gate.
  • PDCSAP processing, dilution, stellar variability, timing variations, and covariance can bias the geometry.
  • Published global fits with physical priors, instrument-specific detrending, and simultaneous sectors remain authoritative.

References

  1. Anderson et al. 2010 — discovery reference listed by the NASA Exoplanet Archive.
  2. Ricker et al. (2015), Transiting Exoplanet Survey Satellite (TESS), doi:10.1117/1.JATIS.1.1.014003.
  3. TESS Team, TESS Light Curves — All Sectors, MAST, doi:10.17909/t9-nmc8-f686; Sector 12 used here.
  4. NASA Exoplanet Archive, saved TAP row retrieved 2026-08-15.