The Demographics of Kepler's Earths and Super-Earths into the Habitable Zone
Abstract
Understanding the occurrence of Earth-sized planets in the habitable zone of Sun-like stars is essential to the search for Earth analogs. Yet a lack of reliable Kepler detections for such planets has forced many estimates to be derived from the close-in (2 < P orb < 100 days) population, whose radii may have evolved differently under the effect of atmospheric mass-loss mechanisms. In this work, we compute the intrinsic occurrence rates of close-in super-Earths (~1-2 R ⊕) and sub-Neptunes (~2-3.5 R ⊕) for FGK stars (0.56-1.63 M ⊙) as a function of orbital period and find evidence of two regimes: where super-Earths are more abundant at short orbital periods, and where sub-Neptunes are more abundant at longer orbital periods. We fit a parametric model in five equally populated stellar mass bins and find that the orbital period of transition between these two regimes scales with stellar mass, like ${P}_{\mathrm{trans}}\propto {M}_{* }^{1.7\pm 0.2}$ . These results suggest a population of former sub-Neptunes contaminating the population of gigayear-old close-in super-Earths, indicative of a population shaped by atmospheric loss. Using our model to constrain the long-period population of intrinsically rocky planets, we estimate an occurrence rate of ${{\rm{\Gamma }}}_{\oplus }={15}_{-4}^{+6} \% $ for Earth-sized habitable zone planets, and predict that sub-Neptunes may be ~ twice as common as super-Earths in the habitable zone (when normalized over the natural log-orbital period and radius range used). Finally, we discuss our results in the context of future missions searching for habitable zone planets.
- Publication:
-
The Astronomical Journal
- Pub Date:
- November 2022
- DOI:
- 10.3847/1538-3881/ac8fea
- arXiv:
- arXiv:2209.04047
- Bibcode:
- 2022AJ....164..190B
- Keywords:
-
- Exoplanets;
- Habitable planets;
- Exoplanet atmospheres;
- Super Earths;
- Mini Neptunes;
- 498;
- 695;
- 487;
- 1655;
- 1063;
- Astrophysics - Earth and Planetary Astrophysics
- E-Print:
- 27 pages, 12 figures, 3 tables