Warm Neptune · sulfur dioxide · JWST context + TESS

GJ 3470 b

A low-mass warm Neptune whose JWST spectrum reveals disequilibrium sulfur chemistry, paired with a reproducible TESS transit fit and a source-graded molecular evidence review.

REAL TESS DATATIMING-AWARE FITCITATION-ONLY · NO BUNDLED SPECTRUMTESTED PIPELINE

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

What the corrected fit shows

Transit supportSUPPORTED (ΔBIC ≥ 10)
Fitted midpoint shift+0.065 h
Model depth6972.3 ± 81.0 ppm
ΔBIC (null − transit)7853.6

The timing-adjusted transit is strongly preferred by ΔBIC = 7853.6. Its fitted midpoint is +0.065 hours from the historical prediction; the model's mid-transit depth is 6972.3 ± 81.0 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 GJ 3470 b
The dotted vertical line is the historical archive prediction; the dashed colored line marks the fitted midpoint (+0.065 h). The smooth curve fits timing, radius ratio, impact parameter, and a local linear baseline.

Explicit model comparison

Linear nullχ² 10061.03 / 2233 dof

BIC = 10076.46

Limb-darkened transitχ² 2184.33 / 2230 dof

BIC = 2222.89

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 depth6972.3 +/- 90.8 ppm
Supported / fitted sectors1 / 1
Residual beta range1.12-1.12

The archive prediction was timing-adjusted independently in 1 fitted sector(s) (S44), of which 1 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 1.12-1.12). The robust inverse-variance model depth across supported sectors is 6972.3 +/- 90.8 ppm; a sector-to-sector Q test requires at least two supported sectors. 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 GJ 3470 b
Independent sector transit fits. Reproduced from the committed public TESS SPOC files.
Sector depth consistency for GJ 3470 b
Sector depth consistency. Reproduced from the committed public TESS SPOC files.
Residual RMS time-averaging diagnostic for GJ 3470 b
Residual RMS time-averaging diagnostic. Reproduced from the committed public TESS SPOC files.

Atmospheric evidence: detection, limit, or unknown?

Evidence scope — citation only; no spectrum bundled. The molecular table and evidence graphic summarize the cited retrieval. This repository does not contain or reanalyze a reduced planetary spectrum.

The cited joint JWST, Hubble, and Spitzer retrieval reports four molecules above 3 sigma and interprets SO2 as disequilibrium photochemistry. This repository audits those published claims but does not re-run the atmospheric retrieval because its reduced spectrum is not bundled here.

Source-graded atmospheric evidence
Literature evidence is kept separate from calculations reproduced in this repository.
SpeciesStatusEvidenceBasis
SO2reported detection>3 sigmajoint atmospheric retrieval
H2Oreported detection>3 sigmajoint atmospheric retrieval
CO2reported detection>3 sigmajoint atmospheric retrieval
CH4reported detection>3 sigma; underabundantjoint retrieval versus equilibrium expectation
O2no evidencenot reportedoxygen-bearing molecules do not imply molecular oxygen

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

The system

Radius4.57 Earth radii
Mass13.90 Earth masses
Orbital period3.336650 days
Transit duration1.898 hours
Semi-major axis0.0355 AU
Equilibrium temperature594 K
Host and distanceGJ 3470 · 29.42 pc
Discovery2012 · Radial Velocity · La Silla Observatory

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 tess2021284114741-s0044-0000000019028197-0215-s_lc.fits, TESS Sector 44, 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 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. Bonfils et al. 2012 — 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 44 used here.
  4. NASA Exoplanet Archive, saved TAP row retrieved 2026-08-15.