Planetary edge trends

I. The inner edge – stellar mass correlation

¹ School of Astronomy and Space Science, Nanjing University, Nanjing 210023, PR China
² Key Laboratory of Modern Astronomy and Astrophysics, Ministry of Education, Nanjing 210023, PR China
³ Institute for Astronomy, School of Physics, Zhejiang University, Hangzhou 310027, PR China
⁴ Department of Physics and Astronomy, University College London, Gower Street, WC1E 6BT London, UK
⁵ Department of Physics, Massachusetts Institute of Technology, Cambridge, MA 02139, USA
⁶ Kavli Institute for Astrophysics and Space Research, Massachusetts Institute of Technology, Cambridge, MA 02139, USA

^★ Corresponding author: jwxie@nju.edu.cn

Received: 3 January 2025
Accepted: 27 May 2025

Abstract

Context. Recent advancements in exoplanet detection have led to over 5900 confirmed detections. The planetary systems hosting these exoplanets exhibit remarkable diversity.

Aims. The position of the innermost planet (i.e., the inner edge) in a planetary system provides important information about the relationship of the entire system to its host star properties, offering potentially valuable insights into planetary formation and evolution processes.

Methods. In this work, based on the Kepler Data Release 25 catalog combined with LAMOST and Gaia data, we investigate the correlation between stellar mass and the inner edge position across different populations of small planets in multi-planetary systems, such as super-Earths and sub-Neptunes. By correcting for the influence of stellar metallicity and analyzing the impact of observational selection effects, we confirm the trend that as stellar mass increases, the position of the inner edge shifts outward.

Results. Our results reveal a stronger correlation between the inner edge and stellar mass (a_in ∝ M_⋆^γ1), with a power-law index of γ₁ = 0.6-1.1, which is larger compared to previous studies. The stronger correlation in our findings is primarily attributed to two factors: first, the metallicity correction applied in this work enhances the correlation; second, the previous use of occurrence rates to trace the inner edge weakens the observed correlation.

Conclusions. Through comparison between observed statistical results and current theoretical models, we find that the pre-main-sequence dust sublimation radius of the protoplanetary disk best matches the observed inner edge-stellar mass. Therefore, we conclude that the inner dust disk likely limits the innermost orbits of small planets, contrasting with the inner edges of hot Jupiters, which are associated with the magnetospheres of gas disks, as suggested by previous studies. This highlights that the inner edges of different planetary populations are likely regulated by distinct mechanisms.