Radius valley scaling among low-mass stars with TESS

¹ Departamento de Astronomía, Universidad de Chile, Camino El Observatorio 1515, Las Condes, Santiago, Chile
² Instituto de Astrofisica, Pontificia Universidad Católica de Chile, Av. Vicuña Mackenna 4860, 7820436 Macul, Santiago, Chile

^★ Corresponding author: harshitha@das.uchile.cl

Received: 3 February 2025
Accepted: 27 August 2025

Abstract

The Transiting Exoplanet Survey Satellite (TESS) has been highly successful in detecting planets in close orbits around low-mass stars, particularly M dwarfs. This presents a valuable opportunity to conduct detailed population studies to understand how these planets depend on the properties of their host stars. The previously observed radius valley in Sun-like stars has also been observed among M dwarfs; however, how its properties vary when compared with more massive stars remains uncertain. We select the volume limited Bioverse stellar catalog, with precise photometric stellar parameters, which was cross-matched with the planet catalog consisting of TESS objects of interests (TOI) candidates and confirmed planets. We detect the radius valley around M dwarfs at a location of 1.64 ± 0.03 R_⊕ and with a depth of approximately 45%. The radius valley among GKM stars scales with stellar mass as R_p ∝ M_∗^0.15±0.04. The slope is consistent, within 0.3σ, with those around Sun-like stars. For M dwarfs, the discrepancy is 3.6σ with the extrapolated slope from the Kepler FGK sample, marking the point where the deviation from previous results begins. Moreover, we do not see a clear shift in the radius valley between early and mid M dwarfs. The flatter scaling of the radius valley for lower-mass stars suggests that mechanisms other than atmospheric mass loss through photoevaporation may shape the radius distribution of planets around M dwarfs. A comparison of the slope with various planet formation and evolution models leads to a good match with pebble accretion models including water worlds, indicating a potentially different regime of planet formation that can be probed with exoplanets around the lowest-mass stars.