An Analysis of the Radius Gap in a Sample of Kepler, K2 and TESS exoplanets orbiting M Dwarf Stars
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| Main Authors: | , , , , , , , , , , , , , |
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| Format: | Preprint |
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2025
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| author | Wanderley, Fábio Cunha, Katia Smith, Verne V. Souto, Diogo Pascucci, Ilaria Behmard, Aida Prieto, Carlos Allende Beaton, Rachael L. Bizyaev, Dmitry Daflon, Simone Hasselquist, Sten Howell, Steve Majewski, Steven R. Pinsonneault, Marc |
| author_facet | Wanderley, Fábio Cunha, Katia Smith, Verne V. Souto, Diogo Pascucci, Ilaria Behmard, Aida Prieto, Carlos Allende Beaton, Rachael L. Bizyaev, Dmitry Daflon, Simone Hasselquist, Sten Howell, Steve Majewski, Steven R. Pinsonneault, Marc |
| contents | 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-M$_{\rm K_{\rm s}}$ calibration that is applied to the sample of M-dwarf planet hosts. The planetary radius distribution displays a gap over R$_{\rm p}$$\sim$1.6-2.0 R$_{\oplus}$, bordered by two peaks at R$_{\rm p}$$\sim$1.2-1.6 R$_{\oplus}$ (super-Earths) and 2.0-2.4 R$_{\oplus}$ (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 (2-3$σ$) from m$\sim$$-$0.10 found previously for FGK dwarfs. This flat slope agrees with pebble accretion models, which include photoevaporation and inward orbital migration. The radius gap as a function of insolation is approximately constant over the range of S$_{\rm p}$$\sim$20-250 S$_{\oplus}$. The R$_{\rm p}$-P$_{\rm orb}$ plane exhibits a sub-Neptune desert for P$_{\rm orb}$$<$2d, that appears at S$_{\rm p}$$>$120 S$_{\oplus}$, being significantly smaller than S$_{\rm p}$$>$650 S$_{\oplus}$ found in the FGK planet-hosts, indicating that the appearance of the sub-Neptune desert is a function of host-star mass. Published masses for 51 exoplanets are combined with our radii to determine densities, which exhibit a gap at $ρ_{\rm p}$$\sim$0.9$ρ_{\oplus}$, separating rocky exoplanets from sub-Neptunes. The density distribution within the sub-Neptune family itself reveals two peaks, at $ρ_{\rm p}$$\sim$0.4$ρ_{\oplus}$ and $\sim$0.7$ρ_{\oplus}$. Comparisons to planetary models find that the low-density group are gas-rich sub-Neptunes, while the group at $<$$ρ_{\rm p}$$>$$\sim$0.7$ρ_{\oplus}$ likely consists of volatile-rich water worlds. |
| format | Preprint |
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arxiv_https___arxiv_org_abs_2509_01930 |
| institution | arXiv |
| publishDate | 2025 |
| record_format | arxiv |
| spellingShingle | An Analysis of the Radius Gap in a Sample of Kepler, K2 and TESS exoplanets orbiting M Dwarf Stars Wanderley, Fábio Cunha, Katia Smith, Verne V. Souto, Diogo Pascucci, Ilaria Behmard, Aida Prieto, Carlos Allende Beaton, Rachael L. Bizyaev, Dmitry Daflon, Simone Hasselquist, Sten Howell, Steve Majewski, Steven R. Pinsonneault, Marc Earth and Planetary Astrophysics Solar and Stellar Astrophysics 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-M$_{\rm K_{\rm s}}$ calibration that is applied to the sample of M-dwarf planet hosts. The planetary radius distribution displays a gap over R$_{\rm p}$$\sim$1.6-2.0 R$_{\oplus}$, bordered by two peaks at R$_{\rm p}$$\sim$1.2-1.6 R$_{\oplus}$ (super-Earths) and 2.0-2.4 R$_{\oplus}$ (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 (2-3$σ$) from m$\sim$$-$0.10 found previously for FGK dwarfs. This flat slope agrees with pebble accretion models, which include photoevaporation and inward orbital migration. The radius gap as a function of insolation is approximately constant over the range of S$_{\rm p}$$\sim$20-250 S$_{\oplus}$. The R$_{\rm p}$-P$_{\rm orb}$ plane exhibits a sub-Neptune desert for P$_{\rm orb}$$<$2d, that appears at S$_{\rm p}$$>$120 S$_{\oplus}$, being significantly smaller than S$_{\rm p}$$>$650 S$_{\oplus}$ found in the FGK planet-hosts, indicating that the appearance of the sub-Neptune desert is a function of host-star mass. Published masses for 51 exoplanets are combined with our radii to determine densities, which exhibit a gap at $ρ_{\rm p}$$\sim$0.9$ρ_{\oplus}$, separating rocky exoplanets from sub-Neptunes. The density distribution within the sub-Neptune family itself reveals two peaks, at $ρ_{\rm p}$$\sim$0.4$ρ_{\oplus}$ and $\sim$0.7$ρ_{\oplus}$. Comparisons to planetary models find that the low-density group are gas-rich sub-Neptunes, while the group at $<$$ρ_{\rm p}$$>$$\sim$0.7$ρ_{\oplus}$ likely consists of volatile-rich water worlds. |
| title | An Analysis of the Radius Gap in a Sample of Kepler, K2 and TESS exoplanets orbiting M Dwarf Stars |
| topic | Earth and Planetary Astrophysics Solar and Stellar Astrophysics |
| url | https://arxiv.org/abs/2509.01930 |