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The Occurrence of Earth-sized Planets around M Dwarf Stars

Presentation #403.08 in the session Exoplanets Formation & Evolution (Oral Presentation)

Published onOct 23, 2023
The Occurrence of Earth-sized Planets around M Dwarf Stars

The Kepler mission provided groundbreaking insight into the field of exoplanet demographics. Yet our understanding of the Kepler sample has evolved over time following development of statistical techniques and updated catalogs. Gaia-revised stellar parameters revealed that most stars (and their planets) are larger and hotter than previously believed (Berger et al. 2020), bringing into question previous results that could not have incorporated such changes. This includes seminal studies of Kepler’s M dwarf stars and their demographic trends with stellar mass, and their occurrence of Earth-sized habitable zone planets. Refining the latter is especially relevant for both current and future missions seeking to detect such worlds.

We present an updated investigation into Kepler’s sample of Earth-sized planets orbiting M dwarf stars, incorporating modern parameters and statistical considerations. Because there are now few detections of Earth-sized planets at low instellations, we developed a set of forward models to predict an occurrence rate of 8.58+17.94-8.22% for Earth-sized planets in the conservative habitable zone. This result is consistent with previous estimates (Dressing & Charbonneau 2015, Hsu et al. 2020) but notably more uncertain, placing limits on the statistical power of the updated Kepler sample.

When comparing with similarly comprehensive studies of Sun-like stars (Kunimoto & Matthews 2020, Bergsten et al. 2022), we found that Earth-sized habitable zone planets are just as common around M dwarfs as they are around FGKs. We also find consistent occurrence rates between our predominantly early M dwarf sample and that of mid-to-late M dwarfs (Ment & Charbonneau 2023). This directly impacts how the population of small planets varies with stellar mass, which is important for our understanding of rocky planet formation and the ongoing search for exo-Earths.

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