An Earth-sized Planet around an M5 Dwarf Star at 22 pc

TL;DR

This paper reports the discovery of an Earth-sized planet orbiting an M5 dwarf star at 22 parsecs, confirmed through multiple observations, with initial detection from K2 and TESS data, and characterized via follow-up spectroscopy and imaging.

Contribution

First detection and confirmation of an Earth-sized planet around a very low-mass M5 dwarf star using combined space-based and ground-based data.

Findings

Planet radius: 1.015±0.051 R_⊕

Planet mass: 3.0±2.7 M_⊕ (upper limit 7.5 M_⊕)

Low false positive probability (2×10⁻⁴)

Abstract

We report on the discovery of an Earth-sized transiting planet ($R_p=1.015\pm0.051\,R_\oplus$) in a $P=4.02$ day orbit around K2-415 (EPIC 211414619), an M5V star at 22 pc. The planet candidate was first identified by analyzing the light curve data by the K2 mission, and is here shown to exist in the most recent data from TESS. Combining the light curves with the data secured by our follow-up observations including high-resolution imaging and near infrared spectroscopy with IRD, we rule out false positive scenarios, finding a low false positive probability of $2\times 10^{-4}$. Based on IRD's radial velocities of K2-415, which were sparsely taken over three years, we obtain the planet mass of $3.0\pm 2.7\,M_\oplus$ ($M_p<7.5\,M_\oplus$ at $95\,\%$ confidence) for K2-415b. Being one of the lowest mass stars ($\approx 0.16\,M_\odot$) known to host an Earth-sized transiting planet, K2-415 will be an interesting target for further follow-up observations, including additional radial velocity monitoring and transit spectroscopy.