What the corrected fit shows
The timing-adjusted transit is strongly preferred by ΔBIC = 189.2. Its fitted midpoint is -0.035 hours from the historical prediction; the model's mid-transit depth is 605.9 ± 57.8 ppm. The support decision uses ΔBIC ≥ 10; timing-search p-values are not presented as blind-detection probabilities.
Explicit model comparison
BIC = 2630.27
BIC = 2441.04
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
The archive prediction was timing-adjusted independently in two fitted sectors (S11 and S38); both meet ΔBIC ≥ 10. Formal depth errors are inflated by √max(reduced χ², 1) and by the residual time-averaging beta factor. The supported-sector inverse-variance depth is 604.1 ± 155.4 ppm; Cochran Q = 0.00 for 1 dof (p = 0.9857). This scalar inflation addresses underestimated scatter and short-timescale correlation but is not a Gaussian-process covariance model.
Published planetary spectrum
Across 106 bins, the weighted-flat model gives χ²/dof = 128.4/105. Under independent Gaussian wavelength-bin errors, this test does not reject flatness at 5%; it does not prove exact flatness. All 106 leave-one-bin-out reruns remain above 5%, while showing that the numerical p-value is threshold-adjacent. Four archived metallicity-grid models are compared after fitting one vertical offset; the source-provided rejection metadata are retained separately. These diagnostics are not an atmospheric retrieval.
See methods, validation, claim limits, and the machine-readable comparisons.
Atmospheric evidence: detection, limit, or unknown?
This is an informative non-detection. The declared flat-line test does not identify H2O, CO2, CO, CH4, or O2. Under a 0.1-bar opaque-pressure assumption, the source paper excludes its tested clear-atmosphere models below 250 times solar metallicity and mean molecular weight below about 6 g/mol. These are conditional model-grid limits, not a prior-independent composition measurement.
| Species | Status | Evidence | Basis |
|---|---|---|---|
| H2-rich atmosphere | model space excluded | <250x solar excluded | source grid; 0.1-bar opaque pressure |
| H2O / CO2 / CO / CH4 | not detected | 2.8–5.2 µm spectrum | no resolved molecular feature |
| O2 | no evidence | not constrained | flatness is not oxygen evidence |
Primary source: Alderson et al. 2024, JWST COMPASS. Oxygen-bearing molecules are not detections of molecular oxygen (O2) and are not, by themselves, biosignatures.
The system
| Radius | 1.70 Earth radii |
|---|---|
| Mass | 4.53 Earth masses |
| Orbital period | 3.816730 days |
| Transit duration | 1.805 hours |
| Semi-major axis | 0.0422 AU |
| Equilibrium temperature | 871 K |
| Host and distance | TOI-836 · 27.50 pc |
| Discovery | 2023 · Transit · Transiting Exoplanet Survey Satellite (TESS) |
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 tess2019112060037-s0011-0000000440887364-0143-s_lc.fits, TESS Sector 11, 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.
- The archived spectrum provides marginal errors but no wavelength covariance matrix; spectral p-values assume independent Gaussian bins.
- A non-rejected flat model does not prove the absence of an atmosphere. Metallicity limits apply only to the source paper’s model grid and pressure boundary.
- Published global fits with physical priors, instrument-specific detrending, and simultaneous sectors remain authoritative.
References
- Hawthorn et al. 2023 — discovery reference listed by the NASA Exoplanet Archive.
- Ricker et al. (2015), Transiting Exoplanet Survey Satellite (TESS), doi:10.1117/1.JATIS.1.1.014003.
- TESS Team, TESS Light Curves — All Sectors, MAST, doi:10.17909/t9-nmc8-f686.
- NASA Exoplanet Archive, saved TAP row retrieved 2026-08-15.
- Alderson et al. (2024), The Astronomical Journal 167, 216, doi:10.3847/1538-3881/ad32c9.