EPIC 210897587: A Bright Metal-Poor M Dwarf with Three Transiting Super-Earths

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EPIC 210897587: A Bright Metal-Poor M Dwarf with Three Transiting Super-Earths

We report on the discovery of three transiting super-Earths around EPIC 210897587, a relatively bright early M dwarf (V=12.81 mag) observed during Campaign 13 of the NASA K2 mission. To characterize the system and validate the planet candidates, we conducted speckle imaging and high-dispersion optical spectroscopy, including radial velocity measurements. Based on the K2 light curve and the spectroscopic characterization of the host star, the planet sizes and orbital periods are 1.55_-0.17^+0.20 R_⊕ and 6.34365±0.00028 days for the inner planet; 1.95_-0.22^+0.27 R_⊕ and 13.85402±0.00088 days for the middle planet; and 1.64_-0.17^+0.18 R_⊕ and 40.6835±0.0031 days for the outer planet. The outer planet (EPIC 210897587.3) is near the habitable zone, with an insolation 1.67±0.38 times that of the Earth. The planet’s radius falls within the range between that of smaller rocky planets and larger gas-rich planets. To assess the habitability of this planet, we present a series of 3D global climate simulations assuming that EPIC 210897587.3 is tidally locked and has an Earth-like composition and atmosphere. We find that the planet can maintain a moderate surface temperature if the insolation proves to be smaller than ∼ 1.5 × that of the Earth. Doppler mass measurements, transit spectroscopy, and other follow-up observations should be rewarding, since EPIC 210897587 is one of the optically brightest M dwarfs known to harbor transiting planets.

 

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