An Analysis Of The Radius Gap In A Sample Of Kepler, K2 And TESS Exoplanets Orbiting M Dwarf Stars
Planetary radii are derived for 218 exoplanets orbiting 161 M dwarf stars. Stellar radii are based on an analysis of APOGEE high-resolution near-IR spectra for a subsample of the M-dwarfs; these results are used to define a stellar radius-MKs calibration that is applied to the sample of M-dwarf planet hosts.
The planetary radius distribution displays a gap over Rp∼1.6-2.0 R⊕, bordered by two peaks at Rp∼1.2-1.6 R⊕ (super-Earths) and 2.0-2.4 R⊕ (sub-Neptunes). The radius gap is nearly constant with exoplanetary orbital period (a power-law slope of m=+0.01+0.03−0.04), which is different (2-3σ) from m∼−0.10 found previously for FGK dwarfs.
This flat slope agrees with pebble accretion models, which include photoevaporation and inward orbital migration. The radius gap as a function of insolation is approximately constant over the range of Sp∼20-250 S⊕. The Rp-Porb plane exhibits a sub-Neptune desert for Porb<2d, that appears at Sp>120 S⊕, being significantly smaller than Sp>650 S⊕ found in the FGK planet-hosts, indicating that the appearance of the sub-Neptune desert is a function of host-star mass.
Published masses for 51 exoplanets are combined with our radii to determine densities, which exhibit a gap at ρp∼0.9ρ⊕, separating rocky exoplanets from sub-Neptunes. The density distribution within the sub-Neptune family itself reveals two peaks, at ρp∼0.4ρ⊕ and ∼0.7ρ⊕. Comparisons to planetary models find that the low-density group are gas-rich sub-Neptunes, while the group at ρp∼0.7ρ⊕ likely consists of volatile-rich water worlds.
Fábio Wanderley, Katia Cunha, Verne V. Smith, Diogo Souto, Ilaria Pascucci, Aida Behmard, Carlos Allende Prieto, Rachael L. Beaton, Dmitry Bizyaev, Simone Daflon, Sten Hasselquist, Steve Howell, Steven R. Majewski, Marc Pinsonneault
Comments: Submitted to ApJ
Subjects: Earth and Planetary Astrophysics (astro-ph.EP); Solar and Stellar Astrophysics (astro-ph.SR)
Cite as: arXiv:2509.01930 [astro-ph.EP] (or arXiv:2509.01930v1 [astro-ph.EP] for this version)
https://doi.org/10.48550/arXiv.2509.01930
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From: Fábio Carneiro Wanderley
[v1] Tue, 2 Sep 2025 03:56:15 UTC (13,697 KB)
https://arxiv.org/abs/2509.01930
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