Hundreds of TESS exoplanets might be larger than we thought

TL;DR

The paper addresses systematic underestimation of exoplanet radii in TESS literature due to unresolved blending. It introduces and validates the TESS-Gaia Light Curves (TGLC) deblending method, comparing sector-by-sector fits against literature values and Kepler benchmarks. The key finding is a median radius bias of about $6\%$ for TESS-dependent planets, corresponding to a $\sim20\%$ downward revision in densities, with significant shifts in mass–radius relations and possible increases in water-world interpretations. The work underscores the critical need for deblended photometry to accurately characterize exoplanet populations and informs target selection for atmospheric studies and formation theories.

Abstract

The radius of a planet is a fundamental parameter that probes its composition and habitability. Precise radius measurements are typically derived from the fraction of starlight blocked when a planet transits its host star. The wide-field Transiting Exoplanet Survey Satellite (TESS) has discovered hundreds of new exoplanets, but its low angular resolution means that the light from a star hosting a transiting exoplanet can be blended with the light from background stars. If not fully corrected, this extra light can dilute the transit signal and result in a smaller measured planet radius. In a study of hundreds of TESS planet discoveries using deblended light curves from our validated methodology, we show that systematically incorrect planet radii are common in the literature: studies using various public TESS photometry pipelines have underestimated the planet radius by a weighted median of $6.1\% \pm 0.3\%$, leading to a $\sim20\%$ overestimation of planet density. The widespread presence of these biases in the literature has profoundly shaped-and potentially misrepresented-our understanding of the exoplanet population. Addressing these biases will refine the exoplanet mass-radius relation, reshape our understanding of exoplanet atmospheric and bulk composition, and potentially inform prevailing planet formation theories.

Figures (3)

• Figure 1: TESS-free, TESS-dependent, and Kepler literature planet-to-star radius ratios compared to fitted TGLC-fitted values. a, The inverse-variance weighted distribution of the fractional difference in radius ratios ($f_p$) between TGLC and literature values for TESS-free (gray) and TESS-dependent (orange) planets. b, The same distribution for Kepler planets (blue). The vertical dashed line and shaded region represent the medians of each distribution and the $1\sigma$ uncertainties of the medians estimated via bootstrap resampling. The black vertical dotted line is at $f_p = 0$ for reference. The TGLC-fitted radius ratios statistically agree with literature values for the less diluted TESS-free and Kepler planets, but disagree for TESS-dependent planets, implying a systematic underestimation of their radii in the literature.
• Figure 2: Planet mass-radius and mass-density distributions of literature and TGLC-fitted values. a, Mass-radius distribution of small TESS planets. b, Mass-density distribution of small TESS planets. Both panels include the high-precision planet sample with TESS-free literature values (gray diamond) and TESS-dependent TGLC-fitted values (black empty circle). The error bars represent $1\sigma$ Gaussian standard deviations. For each TESS-dependent TGLC-fitted value, a line connects it to the corresponding literature value, where the color of the line shows whether it increased (green) or decreased (orange) from the literature value. We also include theoretical models of planet compositions for the Earth-like (red), water worlds (blue), and rocky planets with atmospheres (brown). The last model accounts for the boil-off initial conditions (solid brown) and a range of agnostic initial conditions (region between dashed brown). Earth and Neptune are included for reference.
• Figure 3: Probabilistic radius-density relations for small TESS planets. a, Probabilistic radius-density relations fitted to TESS-free and TESS-dependent literature values. b, Probabilistic radius-density relations fitted to TESS-free and TESS-dependent TGLC-fitted values. The figure includes the high-precision planet sample with TESS-free literature values (gray), TESS-dependent literature values (orange), and TESS-dependent TGLC-fitted values (black). The error bars represent $1\sigma$ Gaussian standard deviations. Probability density maps (light gray) are shown together with the most probable models. From small to large radii, the line components correspond to three planet compositions: rocky planets (red), water worlds (blue), and sub-Neptunes (brown). Dashed lines indicate regions where planetary populations overlap in radius space. TGLC-fitted radii for TESS planets yield a broader and more populated water world regime, suggesting a modestly stronger statistical preference for their existence compared to the model using literature values.