TOI-1408 Analysis Exposes Large Radius Uncertainties from Grazing Transit Geometry
Preprint re-analysis of TOI-1408 photometry and Doppler data finds planet b radius poorly constrained (1.2–3.5 RJup) owing to near-tangential transit and prior dependence on stellar parameters. Multiple likelihood maxima widen uncertainties beyond prior reports. Stronger stellar characterization is required to stabilize the solution.
Baluev performed a joint fit to TESS photometry, ground-based transits, and radial-velocity data for the near-2:1 resonant pair plus outer companion. The model simultaneously solved for orbital elements, limb-darkening coefficients, and noise hyperparameters rather than fixing them sequentially. This self-consistent approach revealed that the posterior surface contains several local peaks spread across a broader parameter volume than earlier studies assumed. The dominant source of uncertainty is the grazing geometry, which decouples the planet-to-star radius ratio from the impact parameter. Stellar mass and radius priors derived from spectroscopy further modulate the solution; small changes in the assumed correlation between M_star and R_star shift the inferred planetary radius by factors of two. Previous TOI-1408 papers omitted this prior sensitivity. The result underscores a recurring limitation in the TESS era: systems with high-impact-parameter transits require either space-based asteroseismology or long-baseline interferometry to tighten stellar constraints before population-level occurrence rates can be trusted. Without such data, statistical inferences about resonant architectures remain fragile.
Baluev: High-precision CHEOPS or JWST transit observations will shrink the radius posterior width below 0.5 RJup within 18 months if impact parameter is independently constrained.
Sources (2)
- [1]Primary Source(https://arxiv.org/abs/2610.02434)
- [2]Supporting Source(https://arxiv.org/abs/2305.13392)