Precise Parameters from Bayesian Spectral Energy Distribution Fitting Indicate Thermally Driven Mass Loss Likely Driver of Radius Valley

Abstract Several planet formation models have been proposed to explain the gap in the population of planets between 1.8 R ⊕ to 2.0 R ⊕ known as the “radius valley.” To apply these models to confirmed exoplanets, accurate and precise host-star and planet parameters are required to ensure the observed measurements correctly match model predictions. Previous studies have emphasized the need for a larger, more precise sample to further confirm dominant formation processes. By enhancing standard spectral energy distribution fitting using Bayesian methods, we derived highly accurate and precise host-star and planet parameters. Specifically, we achieved median fractional uncertainties for stellar and planet radii of 2.4% and 3.4%, respectively. We then produced the largest, most precise sample to date of 1923 planets when compared to previous studies. This full sample, as well as a sample filtered for host stellar masses between 0.8 and 1.2 M ⊙ , were then used to derive the slope and position of the radius valley as a function of orbital period, insolation flux, and stellar mass to compare them to predictive models and previous observational results. Our results are consistent with thermally driven mass loss with a planet radius versus orbital period slope of <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:msub> <mml:mrow> <mml:mi>R</mml:mi> </mml:mrow> <mml:mrow> <mml:mi>p</mml:mi> </mml:mrow> </mml:msub> <mml:mo>=</mml:mo> <mml:msup> <mml:mrow> <mml:mi>P</mml:mi> </mml:mrow> <mml:mrow> <mml:msubsup> <mml:mrow> <mml:mo>−</mml:mo> <mml:mn>0.142</mml:mn> </mml:mrow> <mml:mrow> <mml:mo>−</mml:mo> <mml:mn>0.006</mml:mn> </mml:mrow> <mml:mrow> <mml:mo>+</mml:mo> <mml:mn>0.006</mml:mn> </mml:mrow> </mml:msubsup> </mml:mrow> </mml:msup> <mml:msup> <mml:mrow> <mml:mi>e</mml:mi> </mml:mrow> <mml:mrow> <mml:msubsup> <mml:mrow> <mml:mn>0.896</mml:mn> </mml:mrow> <mml:mrow> <mml:mo>−</mml:mo> <mml:mn>0.010</mml:mn> </mml:mrow> <mml:mrow> <mml:mo>+</mml:mo> <mml:mn>0.012</mml:mn> </mml:mrow> </mml:msubsup> </mml:mrow> </mml:msup> </mml:math> for the full sample, leaning toward core-powered mass loss. The planet radius versus insolation flux slope of <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:msub> <mml:mrow> <mml:mi>R</mml:mi> </mml:mrow> <mml:mrow> <mml:mi>p</mml:mi> </mml:mrow> </mml:msub> <mml:mo>=</mml:mo> <mml:msup> <mml:mrow> <mml:msub> <mml:mrow> <mml:mi>S</mml:mi> </mml:mrow> <mml:mrow> <mml:mi>p</mml:mi> </mml:mrow> </mml:msub> </mml:mrow> <mml:mrow> <mml:msubsup> <mml:mrow> <mml:mn>0.136</mml:mn> </mml:mrow> <mml:mrow> <mml:mo>−</mml:mo> <mml:mn>0.014</mml:mn> </mml:mrow> <mml:mrow> <mml:mo>+</mml:mo> <mml:mn>0.014</mml:mn> </mml:mrow> </mml:msubsup> </mml:mrow> </mml:msup> <mml:msup> <mml:mrow> <mml:mi>e</mml:mi> </mml:mrow> <mml:mrow> <mml:msubsup> <mml:mrow> <mml:mo>−</mml:mo> <mml:mn>0.085</mml:mn> </mml:mrow> <mml:mrow> <mml:mo>−</mml:mo> <mml:mn>0.030</mml:mn> </mml:mrow> <mml:mrow> <mml:mo>+</mml:mo> <mml:mn>0.031</mml:mn> </mml:mrow> </mml:msubsup> </mml:mrow> </mml:msup> </mml:math> for the filtered sample leaned toward photoevaporation. Also, the slope as a function of stellar mass for both samples appears more consistent with thermally driven processes when compared to models and previous studies.